A Nonlinear State Shift: Morphodynamic Thresholds During Progressive Vegetation Uprooting on Alternate Bars

A Nonlinear State Shift: Morphodynamic Thresholds During Progressive Vegetation Uprooting on Alternate Bars | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article A Nonlinear State Shift: Morphodynamic Thresholds During Progressive Vegetation Uprooting on Alternate Bars Saqib Habib, Norio Tanaka This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7909292/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract Vegetation fundamentally regulates river-bar morphology, yet how bars respond when vegetation is progressively removed remains poorly understood. Flume experiments under two steady flows using a two-stage protocol were conducted: Stage 1 trimmed about 30% from the leading edge of an apex patch; Stage 2 cleared the remainder. Bed evolution was analyzed using depth-normalized relief, areal aggradation-degradation fractions, lateral mass-balance indices metrics, and thalweg-based wavelength. Partial removal (Stage 1) triggered an abrupt morphodynamic transition: bed aggradation surged from 20–25% to 56–77%, marking a threshold shift from scour-dominated to deposition-dominated conditions and reorganizing the entire bar–wake system. Complete removal (Stage 2) stabilized this configuration, with deposition remaining dominant and the flow wake lengthening and reattaching farther downstream. At higher discharge, bar wavelength expanded by ~ 10–59%, reflecting longer wakes and reduced roughness, while the lower discharge mainly deepened local relief without major re-spacing. Morphodynamically, Stage 1 acts as the trigger, converting a forced, asymmetric deflector bar into a diffusively depositional form; Stage 2 acts as the stabilizer, allowing the reach to relax toward a free-bar template governed by intrinsic flow–sediment dynamics. Practically, these findings highlight that partial vegetation loss can induce threshold instability, creating scour hotspots. In contrast, complete clearing tends to redistribute sediment more evenly and stabilize bar spacing—offering direct guidance for river restoration and vegetation-management design. Vegetation dynamics sandbar morphology vegetation uprooting erosion deposition. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 1. Introduction Over recent decades, river science has shifted from a static, discipline-fragmented view to a unified biomorphodynamic framework [ 1 , 2 ]. Traditionally, morphology was analyzed using classical mechanics with equilibrium emphasis and separate geologic/hydrologic/biologic influences [ 1 ]. Accumulating evidence shows this is inadequate for natural complexity; instead, a biomorphodynamic perspective recognizes reciprocal interactions among flow, sediment, and vegetation as a single system [ 3 ]. Recent synthesis shows that emergent, submerged, and flexible canopies systematically modify turbulence, shear, dispersion, and sediment transport, driving bar-scale adjustments and channel-pattern shifts in vegetated rivers [ 4 ]. Within this framework, riparian vegetation is a powerful geomorphic agent: plants increase hydraulic roughness, promote sedimentation, and stabilize banks via roots [ 2 ]. These reciprocal plant–flow–sediment interactions have significant implications for management and restoration [ 3 ]. The practical impact of this feedback is substantial for river management and restoration. For example, dams reduce flood frequency/magnitude [ 2 , 5 ], enable vegetation encroachment on bars and floodplains, stabilize surfaces, and potentially shift channels from braided to meandering patterns—altering capacity and habitat [ 6 ]. Colonization of bare alluvial surfaces (e.g., nascent sandbars) by pioneer species initiates biogeomorphic succession—co-evolution of landforms and plant communities [ 2 , 7 , 8 ]. Pioneer traits include prolific, easily dispersed propagules (“invader”), rapid growth, and tolerance of drought or temporary flooding [ 9 ]. Many riparian pioneers, such as willows ( Salix spp.) and cottonwoods ( Populus spp.), show remarkable life-history plasticity; for example, they can resprout after being broken or buried by sediment (an "endurer" strategy) and withstand prolonged flooding (a "resister" strategy) [ 7 ]. This adaptability is essential for survival in dynamic river environments, where conditions can change quickly with each flow event [ 10 ]. Vegetation establishment on sandbars depends on hydrogeomorphic factors across scales [ 11 , 12 ]. At the broad landscape scale, the river's flow regime is the primary driver [ 9 ]. At the landscape scale, the flow regime controls when/where moist bare sediment becomes available. This creates a “recruitment box”: many pioneers synchronize dispersal/germination with the spring-flood recession, exposing nursery sites [ 13 , 14 ]. Within bars, elevation, substrate texture, and soil moisture are critical [ 13 , 15 ]; higher, less-scoured surfaces and finer (silt/sand) substrates that retain moisture favor first-season roots [ 11 ]. Once established, vegetation becomes an ecosystem engineer, altering local hydraulics and morphology [ 2 ]. Emergent plants increase hydraulic roughness, creating zones of reduced flow velocity and lower bed shear stress [ 16 ]. This localized deceleration promotes sediment deposition, enabling vegetated sandbars to grow larger, higher, and more stable than unvegetated counterparts [ 17 ]. Effects scale with stem density, patch extent, and permeability [ 16 , 18 ]. At the grain scale, incipient sediment motion in vegetated open-channel flow can be predicted using a critical depth-averaged velocity; notably, the derived threshold decreases as vegetation density increases [ 19 ]. The geomorphic influence of vegetation extends below the surface, where plant roots mechanically reinforce sediment [ 20 ]. The type of erosion protection provided is closely linked to the plant's root architecture. Fibrous systems (grasses/sedges) form shallow root mats that resist surface erosion in low-energy flows, whereas deeper, rigid taproots (woody plants) resist deeper scour and mass failure during high-energy floods [ 21 , 22 ]. Hence, landform stability depends on the collective root architecture relative to river erosional forces. Although vegetation enhances geomorphic stability, extreme floods can remove even well-established plants. Accurately predicting the resilience of vegetated landforms requires an understanding of two primary uprooting mechanisms, which differ based on plant development and sediment erosion [ 23 ]. The first type, Type I uprooting, is a Drag-induced failure that occurs instantaneously when hydrodynamic forces on the stem and leaves surpass the root system’s anchoring strength. This process primarily affects young, shallowly rooted seedlings [ 23 , 24 ]. In contrast, Type II uprooting is a Scour-mediated failure, typically affecting established vegetation with stronger roots. Drag force alone does not suffice; instead, removal occurs gradually as localized scour erodes sediment from the root mass, weakening anchorage until a threshold is reached [ 23 , 25 , 26 ]. Such scour is often accelerated by powerful horseshoe vortices forming at the patch’s upstream edge, resulting in trench-like erosion patterns and higher vulnerability for plants near this edge [ 18 ]. Removal of riparian vegetation—by natural uprooting or deliberate clearing—can produce long-lasting morphological change. Without vegetative stabilization, channels are prone to increased bank erosion and widening and may shift from single- to multi-thread patterns [ 2 , 27 ]. Vegetation clearing can cause unintended channel enlargement through loss of root cohesion [ 28 ]. Over time, the decay of roots after vegetation loss further reduces slope stability and increases susceptibility to failure [ 29 ]. This weakening may produce preconditioned landforms for catastrophic collapse during major floods. At Japan’s Chikuma River Bridge, an unvegetated, non-cohesive sandbar was eroded entirely during Typhoon Hagibis (2019) [ 30 ], contributing to severe levee damage. While the end-states of fully vegetated vs. bare channels are well documented, the transient morphodynamic pathway between them—especially the response of alternate bars to progressive, partial removal—remains poorly understood [ 2 , 31 ]. Prior work emphasizes end-members or seedling-scale mechanics, overlooking meso-scale dynamics during patch degradation. This issue is not merely academic. Removing a leading edge transforms a sheltered wake into an exposed erosional front. Assuming linear responses to partial clearing risks design errors in management/restoration. Quantifying morphodynamic adjustments during these transient stages is therefore a critical, unresolved challenge. To address this challenge, this study uses a controlled flume experiment to quantify (1) the morphodynamic response of alternate bar topography to the progressive, staged removal of a vegetation patch, and (2) track the evolution of scour/deposition around and within the patch using quantitative morphodynamic metrics. These objectives elucidate the progression from vegetated to bare states, informing management/restoration. 2. METHODOLOGY This study was conducted using a multi-phase laboratory flume experiment designed to systematically examine the morphodynamic response of alternate sandbars to the establishment and progressive removal of vegetation. The experimental program comprised three phases: (1) creation of a stable, non-migrating alternate bar system as a geomorphic baseline, (2) establishment of vegetation on these bars till morphological equilibrium was reached, and (3) successive staged removal of vegetation to simulate gradual uprooting and assess the associated transient, nonlinear morphological adjustments. 2.1 Experimental facility, setup and materials Experiments were performed in a rectangular flume measuring 15 m in length, 0.5 m in width, and 0.5 m in depth at Saitama University in Japan. The flume’s transparent glass sidewalls allowed direct flow visualization and bedform observation. A closed-circuit pump maintained a constant water discharge, monitored at the downstream triangular V-notch weir (Fig. 1 (a)). The movable bed consisted of a 0.1 m thick layer of uniform, non-cohesive quartz sand with a median grain size ( d 50 ) of 0.875 mm and a density ( ρ s ) of 2,650 kg/m³. Table 1 shows the sediment and experimental hydraulic parameters. Recent literature confirms that sand in this size range transition directly from plane bed to dunes under the hydraulic conditions applied in this study [ 32 ]. Table 1 Sediment and Hydraulic Parameters Parameter Symbol Unit Q 1 Q 2 Sediment Properties Material Uniform, non-cohesive quartz sand Median Grain Size d 50 mm 0.875 Fluid Density ρ kg/m³ 1,000 Sediment Density ρ s kg/m³ 2,650 Sediment Influx** Q b kg/s 0.0033 0.00145 Hydraulic Conditions Initial Bed Slope* s m/m 1/200 Discharge Q m³/s 0.0025 0.003 Initial Water Depth* h cm 1.45 1.75 Froude Number** Fr - 0.91 0.83 Shields Parameter** ϑ - 0.050 0.061 Run Time (Phase I, Phase III) T 1 hour 6 5 Run Time (Phase II) T 2 hour 4 Note : * Measured along the center of the channel, ** calculated using the equations for the initial settings for sandbar formation, denominators 1 and 2 represent the discharge Q 1 and Q 2 parameters, respectively. At the flume inlet, a 0.1 m wide transverse block along the left channel wall created a steady hydraulic perturbation that generated a stationary alternate bar ( m = 1) downstream, as shown in the schematic diagram in Fig. 1 (b). This hydraulic forcing method is a well-established technique for generating a stationary bar, providing a stable geomorphic template for systematically examining the effects of vegetation [ 33 ]. Pioneer vegetation was simulated using rigid wooden cylinders with a diameter of 4 mm and a height of 0.18 m, in a fully emergent condition. Following the prior experimental model [ 34 ] pioneer vegetation species such as willow ( Salix spp.) were scaled at a 1:50 geometric scale, corresponding to a typical trunk diameter of ~ 0.2 m in the field. Cylinders were arranged in a dense staggered pattern (relative spacing G/D = 2.2; G = clear spacing between cylinders) to form a semicircular patch 0.3 m in radius, positioned on the sandbar apex facing the flow (Fig. 1 (c); Table 2 : vegetation patch characteristics). Figure 1 (d) shows the physical installation of emergent cylinders on the 0.1 m sand layer. These details address patch porosity and frontal obstruction, which are used later to interpret wake deposition and edge scour. Although rigid cylinders do not capture the flexibility of natural plants, they are a widely accepted proxy for reproducing the bulk hydraulic resistance and flow obstruction effects of vegetation in laboratory experiments [ 35 , 36 ]. Table 2 Characteristics of Simulated Emergent Vegetation Patch Parameter Symbol Value Unit Scaled vegetation cylinder Material Rigid wooden cylinders Diameter D 4 mm Height h v 0.18 m Scaling and Arrangement Geometric Scale - 1:50 - Equivalent Field Trunk Diameter - ~ 0.2 m Arrangement Pattern - Staggered - Relative Spacing G / D 2.2 - Patch Geometry Shape Semicircular Radius - 0.3 m This study focuses on morphodynamics under low-flow, subcritical hydraulic conditions, which are representative of the periods during which vegetation is established and stabilized. While high-flow events generate bare surfaces, stabilization and vegetation colonization predominantly occur during subsequent low-flow phases. Therefore, experiments were conducted under subcritical flow with Froude number ( Fr) < 1. 2.2 Experimental procedure The initial experimental phase aimed at creating a stable, non-migrating alternate bar serving as a baseline geomorphic reference. Hydraulic parameters were selected based on established regime diagrams for alternate bar formation [ 37 ]. The procedure began with a sand bed flattened to an initial slope ( s ) of 1/200. The experiment was conducted on two flow cases to bracket low flow morphodynamics: Q 1 = 0.0025 m³ s⁻¹ and Q 2 = 0.003 m³ s⁻¹. The initial water depths were h₁ ≈1.45 cm and h₂ ≈1.75 cm, yielding Fr ≲ 0.9. Sediment was fed at the inlet at a rate calculated to match the channel's transport capacity for Phase I only [ 38 ], thereby preventing net bed aggradation or degradation. The system reached dynamic equilibrium under subcritical flow conditions (Table 1 ). The Shields parameter is a dimensionless number that represents the ratio of the fluid force on a sediment particle to the gravitational force acting on it. It is defined in Eq. 1 below. The corresponding Shields parameter ( θ ), which determines when sediment begins to move, was above the critical threshold for motion ( θ cr ≈ 0.047), confirming active bedload transport and morphological development. The run continued for five hours until the system reached dynamic equilibrium, defined as the point where the time-averaged bed slope equaled the water surface slope [ 39 ]. $$\:\theta\:=\frac{\tau\:}{\left(\left(\rho\:-{\rho\:}_{s}\right)g{d}_{50}\right)}$$ 1 where τ (N/m²) is the bed shear stress, ρ and ρ s are the fluid and sediment densities (kg/m³), respectively, g (in m/s²) is gravitational acceleration, and d 50 (mm) is the median grain size. Phase II established a stable vegetated topography. The full semicircular vegetation patch was installed on the apex of the alternate bar formed during Phase I. Clear water scour conditions were applied by maintaining the same flow discharge without sediment feed, ensuring that sediment redistribution around the vegetation patch was due solely to local scour and deposition rather than additional sediment input. The run lasted 4 hours, allowing scour-deposition patterns to stabilize, thus creating the initial condition for disturbance experiments. In Phase III, the transient response of the sandbar was quantified using a two-stage, asymmetric vegetation removal protocol designed to investigate non-linear system responses and potential threshold behaviors. Figure 2 illustrates the staged removal sequence: (a, a’) fully vegetated baseline (V us ); (b, b’) partial leading-edge retreat (V ur1 ); (c, c’) complete removal (V ur2 ), establishing the bare-patch control for transient comparisons. To capture the transient morphodynamic response, a two-stage removal was applied. In Stage 1, an upstream strip of vegetation ( l x1 =0.2 m, representing ≈ 30% of the patch cover) was removed. In Stage 2, the remainder of the patch ( l x2 =0.4 m) was removed. The system was allowed to equilibrate for 4 to 6 hours after each stage. Table 3 shows the Experimental cases and staged removal protocol. Table 3 Experimental Cases and Staged Removal Protocol Discharge Case Experimental Phase Vegetation Cover Uprooting Length ( l x ) Q 1 Case1-NN Phase I 0% - Case1-V us Phase II 100% - Case1-V ur1 -i Phase III - Stage 1 30% 0.2 m Case1-V ur1 -j Phase III - Stage 1 30% 0.2 m Case1-V ur2 -k Phase III - Stage 2 0% 0.4 m Case1-V ur2 -l Phase III - Stage 2 0% 0.4 m Q 2 Case2-NN Phase I 0% - Case2-V us Phase II 100% - Case2-V ur1 -i Phase III - Stage 1 30% 0.2 m Case2-V ur1 -j Phase III - Stage 1 30% 0.2 m Case2-V ur2 -k Phase III - Stage 2 0% 0.4 m Case2-V ur2 -l Phase III - Stage 2 0% 0.4 m Note : The semicircular patch radius is 0.3 m (centerline chord ≈ 0.6 m). Stage-1 removes the leading 0.2 m; Stage-2 removes the remaining 0.4 m (full clearance). Note, NN: un-vegetated bars (Phase I); V us : Upstream Vegetation; V ur : Vegetation uprooting, i and j correspond to 1 hour and 4 hours of Stage-1 (V ur1 ), and k and l to 1 hour and 5 to 6 hours of Stage-2 (V ur2 ) 2.3 Measurements and Morphodynamic Analysis Metrics Longitudinal water-surface and bed profiles were measured along the thalweg with a rail-mounted point gauge (± 0.1 mm), sampled every 0.5 m to compute average slopes. To preserve bedform geometry after each phase, the flume was slowly drained after equilibrium. Time subscripts in planform and cross-section plots denote within-stage snapshots: i and j correspond to 1 hour and 4 hours of Stage-1 (V ur1 ), and k and l to 1 hour and 5 to 6 hours of Stage-2 (V ur2 ). Locations L1–L4 mark the patch front, interior, lee axis, and opposite-bank bar, respectively. The 12-m study reach (2–14 m) was scanned with a rail-mounted, non-contact 2-D laser profiler (LJ-V-7000, Keyence). Elevation data were acquired at 10 cm longitudinal and 2.28 cm transverse spacing, then processed with a custom FORTRAN algorithm to quantify scour and deposition patterns. Bed change is expressed as depth-normalized relief (Δ z / h ), where h is the water depth. Four morphodynamic metrics were derived to describe: (i) Areal fractions ( F ), (ii) Planform asymmetry index ( PAI h ), (iii) bank-wise deposition ( S r ), and (iv) volumetric dominance ( Φ ) responses (Eqs. 2 – 5 ). Areal fractions ( F) are an areal measure of bed change. It is separated into F ₊ and F ₋ , which represent the fraction of the total bed area ( A total ) that experienced aggradation ( Δz > 0) and degradation ( Δz < 0), respectively (see Eq. 2 ). This metric captures the extent of deposition vs. erosion, independent of the magnitude of elevation change. $$\:{F}^{+}=(\text{A}\text{r}\text{e}\text{a}\:\text{w}\text{h}\text{e}\text{r}\text{e}\:{\Delta\:}\text{z}>0)/{A}_{total}\:\text{a}\text{n}\text{d}\:{F}^{-}=(\text{A}\text{r}\text{e}\text{a}\:\text{w}\text{h}\text{e}\text{r}\text{e}\:{\Delta\:}\text{z}<0)/{A}_{total}$$ 2 Planform asymmetry index normalized by h ( PAIₕ ) metric (see Eq. 3 ). This metric cleanly captures any flip in lateral dominance after vegetation uprooting and serves as a scalar indicator of bar re-phasing. $$\:{PAI}_{ₕ}=\frac{\left({⟨\varDelta\:z⟩}_{R}-\:{⟨\varDelta\:z⟩}_{L}\right)}{h}$$ 3 To compute PAI h , the map is split along the channel centerline, defining a left half (L) and a right half (R) of equal width. The planform asymmetry is defined as the difference in mean relief change between the right and left halves, normalized by depth (Eq. 3 ). Then, compute the mean Δ z / h over each half, ⟨ Δz / h ⟩ ᴸ and ⟨ Δz / h ⟩ ᴿ , using all cells (positive and negative). By definition, PAI h >0 indicates a right-leaning bias (more deposition/scour on the right side), PAI h <0 indicates a left-leaning bias, and PAI h = 0 means the changes are laterally balanced. The right-bank deposition share, S r , is a volume-based metric that measures what fraction of the total deposition occurred on the right half of the channel (see Eq. 4 ). This metric complements PAI h by pinpointing which bank (if any) accumulates more deposited material, thus helping to link observed bar-crest growth or migration to one side of the channel. $$\:{S}_{r}=100·{V}_{⁺ᴿ}/({V}_{⁺ᴸ}+{V}_{⁺ᴿ})$$ 4 To compute S r , first compute the total volume-equivalent of deposition in each half of the channel (integrating positive Δz values, normalized by depth). For the left and right halves, sum only the positive Δ z / h values: V ⁺ᴸ = Σ(max( Δz ,0)/ h ) over the left half, V ⁺ᴿ analogously on the right. The volumetric dominance metrics, Φ⁺ and Φ⁻ (see Eq. 5 ), characterize the overall sediment budget of the reach in terms of deposition vs. scour. These metrics weight changes by their depth (volume), so they can reveal whether deposition or erosion dominates the reach even when areal coverage ( F ₊ vs F ₋ ) might suggest a different balance. $$\:{{\Phi\:}}^{+}=100·{V}^{+}/({V}^{+}+{|V}^{-}|)\:\text{a}\text{n}\text{d}\:{{\Phi\:}}^{-}=100-\:{{\Phi\:}}^{+}$$ 5 The total deposited volume D⁺ = Σ[max(Δ z , 0)] (sum of all positive bed changes) and total scour volume D⁻ = Σ[min(Δ z , 0)] (absolute sum of all negative bed changes). To allow comparison between stages, depth-normalized these volumes: V⁺ = D⁺ / h and V⁻ = | D⁻ | / h , using the water depth h . In essence, Φ⁺ represents the percentage of the total sediment volume change that is depositional. Unlike F ₊ (which is an area fraction), Φ⁺ incorporates the magnitude of elevation changes, not just their extent, providing a complementary view of whether deposition or scour is volumetrically dominant. The normalized morphometric indices capture how the channel bed reorganizes as vegetation is removed. The areal deposition fraction ( F ₊ ) measures the proportion of the bed surface experiencing net aggradation and thus indicates whether the system behaves as a depositional or erosional field. Volumetric fractions ( Φ⁺ , Φ⁻ ) measure the share of total bed-volume change due to aggradation vs. scour (magnitude-weighted), so Φ complements F by indicating how deep/substantial the changes are, not just how widespread. The planform asymmetry index ( PAIₕ ) quantifies the lateral tilt of deposition, where positive values represent right-bank dominance typical of deflector-type wakes, while values near zero signify symmetry and balance. The right-bank deposition share ( S r ) expresses how much of the total deposited volume accumulates on the right side of the channel, reflecting the extent of lateral bar migration or confinement. Together, these metrics link directly to bar morphology: high F, Φ , with near-zero PAIₕ and S r ≈ 0.5 imply a broad, laterally even depositional bar, whereas low F , Φ + <0.5 describe a contracted, right-leaning scour zone driven by flow deflection. To expose near-patch hydraulics, we use four patch-aligned locations. L1—leading edge (stagnation) where an ‘edge trench’ forms post-cut; L2—patch center; L3—lee axis (wake core/reattachment path); L4—far-bank crest that collects redistributed sediment. 2.4 River Scaling Translating flume morphodynamics to the river scale is challenging because all similarity constraints cannot be satisfied simultaneously [ 40 ]. The main difficulty comes from the inability to simultaneously satisfy all relevant dimensionless scaling parameters, especially the Froude number and the Shields parameter [ 41 ]. This leads to experimental setups that often employ steeper slopes compared to nature to sustain sediment transport at limited flow depths [ 42 ]. Rather than pursuing perfect geometric or dynamic similarity, which is impractical, this study prioritizes process-based similarity by carefully selecting hydraulic parameters to replicate sediment motion and alternate bar formation dynamics representative of natural systems. Maintaining the Shields parameter above its critical threshold ensures bedload-dominated transport processes. This approach is widely accepted for investigating complex bio-morphodynamic interactions under controlled laboratory conditions [ 40 , 42 ]. 3. RESULTS The morphodynamic response was analyzed under two steady discharges, Case 1: Q 1 = 0.0025 m³ s⁻¹ and Case 2: Q 2 = 0.003 m³ s⁻¹, a forced, non-migrating alternate-bar generated by a transverse inlet block. The experimental sequence was consistent for both discharges: NN (non-vegetated baseline), V us (vegetated equilibrium), V ur1 (Stage 1: partial removal), and V ur2 (Stage 2: complete removal). Representative bed elevation contour maps for each stage are shown in Fig. 3 for Q 1 and Fig. 4 for Q 2 . Vegetation patches were semicircular (radius 0.3 m), emergent, and densely staggered ( G / D ≈ 2.2), positioned on the bar apex facing the flow. The two-stage removal excised 30% of the patch cover in Stage 1 and the remaining 70% in Stage 2, with equilibration periods after each. 3.1 Baseline Morphologies A transverse inlet block generated a forced, non-migrating bar train (mode m = 1), establishing a repeatable baseline. Consistent with linear theory for forced bars at modest aspect ratio ( W /(2 h ) ≈ 14–17) and subcritical Froude numbers ( Fr ≲ 0.9), measured wavelengths at equilibrium were about 10 W ( Q₁ ) and 11 W ( Q₂ ), in line with Phase-I characterization and analytic scaling for hybrid bars [ 43 ]. For moderate width‑to‑depth ( W / h ) and subcritical Froude numbers, the steady-bar framework predicts a most-likely bar mode controlled primarily by W / h , with steady patterns expected under planform or obstacle forcing [ 44 ]. Longitudinal elevation profiles (Fig. 3 (a) and Fig. 4 (a)) show the canonical alternation of shoal and pool, with downstream propagation arrested by the upstream forcing; the bars lengthened and stabilized in place as equilibrium was approached, precisely as described for hybrid trains with localized perturbations. Under equilibrium conditions (V us ), the patch produced a front-edge stagnation trench and a lee deposition corridor, yielding a right-leaning planform. These signatures were present at both discharges and emerged earlier and more strongly at Q₂ than at Q₁ (Fig. 3 (b) and Fig. 4 (b). A finite emergent patch increases drag and intensify lateral flow at the vegetation–clear‑flow interface (Location L1); turbulence production and wake sheltering trap sediment within/behind the patch while diverting the core jet toward the opposite bank [ 35 , 45 , 46 ]. Figure 3 (b) and Fig. 4 (b) display the same phenomena: deposition in and just behind every patch and scour on the opposite bank, with the effect stronger at Q₂ (greater mobility). In this forced‑bar setting, these manifest as a mild lengthening of local crest–trough spacing (storage) without changing the global mode ( m = 1). An experimental study reports that vegetation lengthens wavelength and stabilizes the planform, with stronger expression at higher discharge [ 34 ]. 3.2 State Shift: Areal and Lateral Reorganization After Vegetation Removal 3.2.1 Stage‑1 (V ur1 ): partial, leading‑edge cut Following the Stage 1 removal of the leading ~ 30% of the patch, the morphology changed significantly. The zone of maximum scour shifted from the original patch front to the newly exposed leading edge, and depositional patterns in the lee of the patch were reorganized (Fig. 3 (c), Fig. 4 (c)). Relative to the vegetated baseline (V us ), the Stage-1 truncation immediately reorganizes patch-scale hydraulics by weakening the front-face stagnation and breaking the continuous sheltering within the footprint. “In Q 1 , this is evident by comparing Fig. 3 (b) (Case1-V us ) with the Stage-1 maps in Fig. 3 (c–d) (Case1-V ur1 ): the impingement zone at L1 i and L1 j retreats along the semicircle arc and its peak orange–red signal (scour) diminishes, while scour tongues intrude the canopy interior at L2 i and L2 j as through-patch leakage replaces the former deflection pattern. Downstream, the lee-axis minimum (L3 i/j ) elongates and advects, with a slight rotation consistent with the alternate-bar front. The exact mechanism strengthens under Q 2 : relative to Fig. 4 (b) (Case2-V us ), Fig. 4 (c–d) (Case2-V ur1 ) shows a decisive L1 collapse, a coherent interior-scour core at L2, and a farther-advected L3, consistent with a longer reattachment length at higher discharge. Partial vegetation removal abruptly shifts the bar from scour-dominated to deposition-dominated, re-centering sediment laterally and reducing planform asymmetry, particularly at Q 2 . Channel-scale consequence: a discharge-dependent state shift and re-phasing of the alternate bar initiated by Stage-1. Mechanistically, Stage-1 reproduces natural, scour-assisted uprooting: edge scour undermines rooting, shortens the first reattachment, and flips the bar from a deflector-type wake to a diffuser-type wake. The partial removal of the leading edge breaches this frontal barrier. Rather than deflecting, flow penetrates the patch, where stems dissipate momentum and spread it outward like a hydraulic diffuser. This eliminates the large, sheltered wake, increases turbulence and scour within the patch interior (L2), and creates a more disorganized, advected wake downstream. This hydraulic shift from deflection to diffusion is evident in the morphological response. Under Q 1 , the V us deflector weakens to a momentum diffuser: L1 i/j loses its stagnation anchor, L2 i/j shifts towards scour, and L3 i/j translates modestly. Meanwhile, L4 i/j shows moderate accretion without complete bar reorganization (compare Fig. 3 (c–d) to Fig. 3 (b)). Under Q 2 , the same sequence is amplified: L1 i/j diffuses, L2 i/j scours more strongly, L3 i/j lengthens and shifts farther downstream, and L4 i/j advances more clearly as the far-bank lobe gains dominance (compare Fig. 4 (c–d) to Fig. 4 (b)). 3.2.2 Stage‑2 (V ur2 ): Complete removal Under Q 1 , the complete vegetation removal reinforces Stage-1 trends, establishing a new patch-scale morphology (Fig. 3 (e–f), Case 1-V ur2 ). The stagnation zone disperses: L1 k shows diffuse, weak scour, and L1 l lacks the arc-focused hotspot, confirming the loss of stable impingement. Inside the footprint, a coherent interior-scour core develops at L2 k and persists at L2 l , consistent with sustained scour once the shelter is removed. Lee response intensifies: L3 k ’s wake minimum elongates and shifts further downstream while the far bank bar becomes the dominant depositional feature. L4 k already shows green–blue lobe growth, and by L4 l , the crest is advanced and widened, consistent with a more extended separation length and downstream reattachment. Under Q 2 , this progression is more pronounced (Fig. 4 (e–f), Case2-V ur2 ). L1 k ’s front-face control collapses rapidly and disappears by L1 l . Interior scour at L2 k/l is stronger and more spatially continuous than in Q 1 . At the same time, the lee minimum L3 k extends farther and remains advected at L3 l , indicating a longer reattachment distance and intensified cross-stream momentum exchange. The opposite-bank bar L4 responds vigorously, with a clear crest advance and lobe thickening; the depositional footprint occupies a larger fraction of the reach than in Q 1 , signaling a decisive re-phasing of the alternate-bar pattern at the higher discharge. Relative to the partial leading-edge cut (V ur1 ; Fig. 3 (c–d) Q 1 ; Fig. 4 (c–d) Q 2 ), complete removal (V ur2 ) eliminates residual deflection and yields a persistent diffuser: L1 transitions from a weakened stagnation zone to a diffuse, non-anchoring front; L2 from mixed response to persistent interior scour; L3 lengthens/advects; L4 progresses from incipient to dominant crest advance. Plan-view elevation maps for complete removal (V ur2 ) are shown in Fig. 5 (a–b). Relative to V ur1 , the front-edge trench broadens and shallows, the lee minimum translates farther downstream, and deposition consolidates along the opposite-bank crest. At higher discharges, the depositional footprint occupies a larger fraction of the reach, and the wake reattachment lengthens, consistent with the longer-wavelength bar train that we quantify later. These maps capture the planform expression of the completed re-phasing described in Fig. 3 – 5 . 3.3 Edge-trench onset and wake reorganization across the vegetation (from V us to V ur2 ) At Q 1 , V us exhibits a front-edge trench (Δ z / h ≈ − 1.2; Fig. 6 (a)) and mild lee deposition. Table 4 shows the normalized bed-relief across each discharge. V ur1 disrupts the trench–wake balance: infill begins, and downstream deposition intensifies (Fig. 6 (b)). Relief increases by Δ z / h ≈ + 1.0 (Table 4 ), indicating sediment reallocation from trench to lee. V ur2 consolidates this arrangement, maintaining high deposition and smoothing the relief (Fig. 6 (c)). Overall, at Q 1 , the main morphodynamic work occurs during Stage 1, while Stage 2 primarily stabilizes the newly organized depositional corridor. Table 4 Summary of normalized bed-relief ( Δz/h ) and morphodynamics metrics for Q 1 and Q 2 across stages (V us , V ur1 , V ur2 ) Discharge Location Stage Mean Δz/h trend Areal trend ( F ₊ , F ₋ ) Lateral trend ( PAIₕ , S r ) Volumetric Trend ( Φ⁺ / Φ⁻ ) Dominant process / Remarks Q 1 L1 (Front) V us −1.2 (trench) F ₊ ≈ 25% ≪ F ₋ PAIₕ + 0.23, S r >55% Φ⁺ ≈ 35% / Φ⁻ ≈ 6 % Edge scour- Vegetation deflects flow, creating a deep trench at the front. V ur1 + 0.3 (infilling) F ₊ ≈ 70% ≫ F ₋ PAIₕ ≈ 0, S r ≈ 50% Φ⁺ ≈ 72% / Φ⁻ ≈ 2 % Trench reduction + lee growth, Threshold flip: scour→deposition V ur2 + 0.1 (stable) F ₊ ≈ 73% PAIₕ ≈ 0, S r ≈ 50% Φ⁺ ≈ 74% / Φ⁻ ≈ 2 % Wake stabilizes - Balanced deposition maintained L2 (Interior) All + 0.8–1.1 F ₊ > F ₋ PAIₕ ≈ 0, S r ≈ 50% Φ⁺ ≈ 70–75% / Φ⁻ ≈ 25–30% Core aggradation, lee corridor broadens and levels. L3 (Lee) All −0.1 → +1.0 F ₊ ↑ Slight left-shift Φ⁺ ≈ 75% / Φ⁻ ≈ 2 % Coherent lee-wedge formation, organized wake deposition. Q 2 L1 (Front) V us + 0.3 (weak trench) F ₊ ≈ 20% ≪ F ₋ PAIₕ +0.15, S r >60% Φ⁺ ≈ 30% / Φ⁻ ≈ 7 % Weak scour-edge still armored V ur1 + 1.2 (peak uplift) F ₊ ≈ 56% PAIₕ ≈ 0. S r ≈ 50% Φ⁺ ≈ 68% / Φ⁻ ≈ 3 % Trench uplift and flow contraction - Stronger flip than Q₁ V ur2 + 0.9 (stable) F ₊ ≈ 70% PAIₕ ≈ 0. S r ≈ 50% Φ⁺ ≈ 72% / Φ⁻ ≈ 2 % Diffused trench - Sustained depositional dominance L2 (Interior) All −0.6 → 0.0 → +0.7 F ₊ ≈ Φ ⁺ ↑ Balanced Φ⁺ ≈ 70–75% / Φ⁻ ≈ 25–30% Interior flattening - Loss of the core scour zone L3 (Lee) All −0.7 → +1.1 → +0.9 F ₊ ↑ Slight right-lean Φ⁺ ≈ 75% / Φ⁻ ≈ 2 % Lee fill + downstream translation - longer reattachment, stronger wake Note : Patch Location, L1-Front, L2-Interior, L3-Lee, morphometric indices— F (areal fraction), PAIₕ (lateral asymmetry), Φ (volumetric dominance), and Sᵣ (right-bank share of deposition). At Q 2 , the sequence repeats with stronger dynamics. Under V us , the trench is shallower (Δ z / h ≈ + 0.3; Fig. 6 (d)), and sediment starts bypassing the patch edges. Stage 1 (V ur1 ) triggers a pronounced scour slot at L1 while simultaneously building a strong depositional wedge at L3 (Δ z / h ≈ + 1.1; Table 4 , Fig. 6 (e)). Flow reattachment occurs closer to the patch, shortening the wake and concentrating deposition. V ur2 (Stage 2) further widens the trench and shifts deposition downstream, smoothing the profile toward a free-bar state (Fig. 6 (f)). This promotes greater bar mobility at Q 2 , with longer scour–fill oscillations and more dynamic re-spacing than at Q 1 . 3.4 Normalized morphometrics and areal bias Normalized indices/metrics ( F , Φ, PAIₕ , S r ) show a systematic shift from scour-dominant, right-leaning (V us ) to deposition-dominant, more symmetric states with staged removal across each discharge (Table 4 ; Fig. 7 ). Under the vegetated equilibrium (V us ), both discharges show a clear scour-dominated configuration, with F ₊ ≈ 20–25% and Φ⁺ 0, S r ≈ 60%) (Fig. 7 (c-d)), confirming a flow-deflecting canopy that concentrates shear at the patch front and diverts the core jet laterally. This vegetated morphology thus represents a stable, deflector-type reference state dominated by frontal trenching and localized deposition behind the patch. V ur1 introduces a central morphological pivot. The leading-edge removal weakens the deflector effect, redistributing flow more evenly across the section. Areal deposition expands rapidly ( F ₊ ≈ 55–77%) (Fig. 7 (a). While volumetric accumulation nearly doubles as shown in Fig. 7 (b) ( Φ⁺ ≈ 65–75%), indicating a shift from scour-dominated to deposition-dominant behavior. Lateral indices flatten ( PAIₕ ≈0, S r ≈ 50%), signaling balanced sediment storage on both banks (Fig. 7 (c–d)). Morphodynamically, Stage 1 transforms a confined, vegetation-forced bar into a diffuse depositional corridor. The former trench zone begins to fill, and the downstream wake strengthens—an inflection clearly visible in Fig. 7 and confirmed across all cross-sections in Table 4 . V ur2 completes and stabilizes this transition. The frontal scour diffuses, and broad deposition dominates the planform ( F ₊ ≈ 53–73%, Φ⁺ ≈ 70–80%). Slightly negative PAIₕ values indicate a mild left-lean under some realizations, yet overall, the configuration approaches a laterally balanced free-bar equilibrium. Stage 2, therefore, consolidates the Stage-1 change, yielding a smoother, lower-relief surface where energy distribution and sediment transport become more symmetric (Fig. 7 (a–d). The patch-scale observations (P1–P3) reveal that the strength of this adjustment depends on position within the bar (Fig. 8 (a–b)). At Q 1 , the apex patch (P2) exhibits the strongest Stage 1 flip—from right-biased scour ( PAIₕ ≈ +0.48) to left-leaning deposition ( PAIₕ ≈ −0.1)—while flank patches (P1, P3) show milder shifts due to partial hydraulic shielding. At higher discharge ( Q 2 ), newly mobilized sediment is partly exported downstream, causing local F ₊ to decline slightly. At the same time, Φ⁺ remains high (> 70%), indicating that volumetrically the reach continues to aggrade even if local surfaces fluctuate. Overall, the morphometric indices reveal a non-linear progression of channel adjustment: vegetation imposes asymmetry and scour concentration, partial uprooting reverses it abruptly, and complete removal stabilizes the new, deposition-dominant morphology. 3.5 Longitudinal Adjustment: Bar Wavelength and Phasing Uprooting influences the longitudinal organization of alternate bars by altering both the wavelength ( λ ) and the crest–trough phasing (Fig. 9 ). In the vegetated cases (V us ), the bar exhibits pronounced relief and slightly elongated spacing compared to the non-vegetated reference (NN). Their crests/troughs are clearly out of phase with Phase 1 (alternate bars) over several reaches (e.g., between ~ 0.5–1 m), indicating a vegetation-induced shift of the bar couplet (Fig. 9 (a)). Peak picking on the detrended thalweg shows that the mean wavelength of the vegetated sequence is ≈ 5.6 m, whereas Phase 1 (alternate bars) retains a longer spacing of ≈ 5 m. When discharge increases to Q 2 , the vegetated wavelength remains near ≈ 7 m, while the Phase 1 (alternate bars) wavelength compresses to ≈ 6 m; as a result, V us becomes ~ 10% longer than Phase 1 (alternate bars) (see Fig. 9 (b). V ur1 initiates a measurable longitudinal adjustment, the magnitude of which depends on discharge. At Q 1 , λ contracts modestly—about 4% shorter than NN—signaling the collapse of the vegetative deflector and local infilling behind the former trench. At Q 2 , however, V ur1 produces the opposite effect: wavelength lengthens by + 10–33%, indicating that increased discharge transforms the wake from confined to diffusive. V ur2 reinforces and stabilizes the Stage-1 trajectory. At Q 1 , λ recovers slightly (+ 4% above NN), approaching the natural spacing of free bars, while at Q₂ it increases markedly (+ 43–59%), yielding fewer and more persistent bar cells. The longitudinal thalweg profiles (Fig. 9 (b) clearly show the expansion of low-frequency oscillations and downstream translation of crests, indicating longer morphodynamics cells and slower bar migration. Across Q 1 – Q 2 , V ur1 initiates the state shift (trench decay, corridor formation, modest λ regularization); V ur2 stabilizes it (persistent corridor, symmetric morphometrics, regular wavelength). The wavelength data reveal a scale-dependent re-phasing of bar morphology. Vegetation lengthens and stabilizes the bar pattern, partial removal relaxes this constraint and reorganizes bar rhythm, and complete clearing restores intrinsic flow-controlled spacing. The interplay of discharge and vegetation control defines a non-linear continuum of morphodynamic states, with Stage 1 as the tipping point and Stage 2 as the equilibrium consolidation phase. Together, the two discharges define a coherent trend: uprooting induces a morphodynamic re-phasing where wavelength responds non-linearly to vegetation removal. Stage 1 initiates the bar-length growth; Stage 2 consolidates it, particularly under high discharge. Morphodynamically, this demonstrates that vegetation loss not only reorganizes local scour and deposition but also scales up to alter the fundamental bar spacing and propagation rhythm (Fig. 9 ). 4. DISCUSSION The sequential removal protocol was not just an experimental convenience; it was designed as an intentional process: the leading-edge cut mimics the scour-mediated (Type II) uprooting failure of established plants, where local trenching by horseshoe vortices undermines root anchorage, thereby clarifying why the V ur1 ‘flip’ is abrupt rather than gradual [ 26 ]. This makes the Stage-1 flip directly comparable to natural flood-induced vegetation loss at bar fronts. The initial cylinder embedment depth was set to 0.1 m to ensure firm anchorage, yet it remained shallow enough that scour below this depth would induce uprooting [ 17 ]. During the vegetated equilibrium, localized scour at the patch's hydraulically vulnerable leading edge reduced the local sediment thickness [ 47 , 48 ]. This scour-induced reduction in anchoring depth represents the threshold at which the frontal vegetation becomes vulnerable to uprooting. Therefore, the manual sequential vegetation removal in Phase III is a controlled simulation of this uprooting, allowing for the systematic quantification of the sandbar's morphological response to a known magnitude of disturbance. This study reveals that the progressive removal of vegetation triggers a pronounced, non-linear state shift. Partial, leading-edge removal acts as a threshold disturbance that flips an alternate bar from scour-dominant (~ 20–25% aggrading area) to deposition-dominant (~ 56–77%), indicating a discrete state change rather than linear interpolation between end-members. This Stage-1 response matches the signature of scour-mediated (Type-II) uprooting, where leading-edge trenching undermines anchorage and reorganizes the wake. The following sections synthesize the mechanism, practical implications, and limits on transferability. This marks a threshold behavior—under low flow, partial removal shortens the bar train through localized sediment trapping; under high flow, it releases sediment farther downstream, creating broader, more widely spaced bars. V ur1 thus serves as the principal phase of bar re-organization, corresponding to the morphodynamic “pivot” from a deflector-type wake to a diffuser-type one. Vegetation behaves as a finite deflector that concentrates shear at the patch front and shelters its lee, producing deeper troughs, taller deposits, and longer bar wavelengths than bare beds [ 31 , 34 ]. The vegetated baseline (low F ₊ and Φ⁺ , high F ₋ and Φ − ; PAIₕ >0; S r >50%) is therefore consistent with classic patch-wake hydraulics for wall-attached and mid-channel patches [ 49 ]. Partial removal short-circuits deflector control, shortening reattachment and relaxing spacing toward the free-bar template; field observations similarly report more regular alternate bars formation after removal of roughness elements that had forced irregular patterns [ 50 ]. The Stage 1 removal transformed the patch from a solid flow deflector to a porous diffuser. This hydraulic shift concentrated shear stress at the new leading edge, carving a distinct scour trench (L1). Simultaneously, it allowed flow into the patch interior, eliminating shelter (L2) and promoting organized deposition in its immediate lee (L3) (Fig. 6 ). Longitudinally, the crest–trough couplet contracts immediately downstream (Fig. 9 ), consistent with a shorter reattachment and a depositional lobe shifted toward the far-bank crest. These signatures are expected when wake geometry is controlled by patch size and edge shear, and when partial leading-edge removal or stem flexibility reduces the reattachment length [ 49 , 50 ]. Mechanistically, the sequence mirrors Type-II uprooting: localized edge scour reduces anchorage and lowers the removal threshold into the range of common floods [ 23 , 26 ]. Stage-2 removes the deflector entirely and consolidates the Stage-1 trajectory: the L1 trench diffuses, the lee minimum advects downstream, spacing re-lengthens, and lateral shares remain near balanced (Figs. 6 – 9 ). This relaxation toward a free-bar template aligns with reports that vegetation stabilizes and elongates bars, whereas removal returns systems toward shorter, more mobile bars [ 17 , 51 ]. Patch position matters. Windows closer to the bar crest (P2–P3) show the clearest Stage-1 flip ( F ₊ rises; PAIₕ trends negative) and Stage-2 stabilization near lateral balance, whereas a marginal window (P1) shows weaker swings (Fig. 8 (a–b)), consistent with stronger bar–patch feedback near crests and greater local wavelength control [ 17 ]. At higher flow, more of the new deposition is exported downstream (local F ₊ can remain small while the reach budget Φ⁺ rises), matching the theory that higher discharge promotes more mobile bars with longer reattachment and shorter intrinsic wavelength [ 39 , 43 ]. Across P1–P3 and both discharges, metrics cohere: F ₊ increases, F ₋ declines, PAIₕ and S r move toward balance; spacing contracts near the apex in Stage-1 and re-lengthens in Stage-2, with a stronger, more persistent response at Q 2 (Fig. 8 ). These patterns align with broader eco-morphodynamic feedback: vegetation reduces near-bed stress and traps sediment, stabilizing and elongating bars, whereas frequent uprooting limits colonization and maintains shorter, more mobile bars [ 52 ]. Convergent evidence from planform metrics, cross-sections, and longitudinal profiles (Figs. 6 – 9 ), along with independent studies, supports the uprooting-driven re-phasing of alternate bars [ 17 , 23 , 26 ]. Partial leading-edge clearing concentrates edge shear and shortens the first reattachment, creating a trench hotspot over roughly one to two patch lengths and shifting deposition toward the opposite bank—consistent with patch-wake mechanics observed in flumes and field canopies [ 35 , 52 ]. Accordingly, selective thinning at bar apices for navigation or conveyance can inadvertently destabilize the remaining bar by intensifying local scour and by redistributing deposition laterally. In contrast, complete clearing tends to stabilize spacing and export a larger share of deposition downstream, moving the reach toward a free-bar template—aligning with evidence that vegetation elongates/stabilizes bars and that removal relaxes spacing toward intrinsic morphodynamic modes [ 34 , 45 , 51 ]. Discharge sensitivity should guide timing and monitoring. Higher flows amplify wake length and deposition footprints, increasing the chance that partial clearing will trigger a threshold flip. Therefore, interventions near the rising limb are more likely to produce strong edge trenching and rapid re-phasing. For post-works surveillance, simple planform indices (aggrading-area share F ₊ and right-bank deposition share S r ) provide low-cost early warning of unintended polarity flips or lateral imbalance (Fig. 8 ). Field reports indicate that removing roughness elements can yield more regular alternate bars [ 50 ]. Rigid, emergent cylinders omit reconfiguration and motion-induced drag reduction; flexible or submerged canopies would likely smooth the Stage-1 transition, although the edge-shear/wake mechanism remains the same [ 53 ]. Steady discharge omits rising/falling-limb hysteresis; rising limbs could advance edge trenching, falling limbs could partially backfill, modulating (not negating) the flip predicted by Type-II mechanics [ 25 ]. Clear-water scour emphasizes local trenching and lee organization; sediment-laden floods would shallow trenches and shift more deposition downstream. Fixed banks suppress bank–bar coupling and channel widening; in mobile-bank rivers, lateral adjustment would likely strengthen bar shortening and re-phasing. Normalizing relief by Δ z / h supports stage-wise comparison but coarsens near-bank contrasts; the inlet perturbation gently favors m = 1, biasing reach-scale spacing. Within these bounds, the staged-removal protocol provides a process template for apex patches on alternate bars. 5. CONCLUSION This study demonstrates that the progressive uprooting of vegetation from alternate sandbars induces a threshold-type, non-linear morphodynamic transition. The response to partial removal is not a simple interpolation between the fully vegetated and bare end-member states but rather a distinct dynamic regime. The key findings are summarized below. Partial uprooting causes a rapid polarity flip from scour-dominated to deposition-dominated morphology, revealing that even minor vegetation loss can cross a stability threshold in bar dynamics. Complete uprooting does not reverse this shift but instead stabilizes and consolidates it. The morphodynamic transition is expressed through increased depositional area ( F ₊ ), reduced lateral asymmetry ( PAIₕ ), balanced right-bank deposition ( S r ), and higher volumetric dominance ( Φ⁺ ). Together, these metrics indicate a fundamental re-phasing of the bar from a forced, asymmetric state to a free-bar configuration. Vegetation removal alters the bar-scale geometry—under low discharge ( Q 1 ), wavelength changes are minor (± 4%), but at high discharge ( Q 2 ), bars elongate by 10–60%, reflecting longer wakes and slower bar migration. This scaling confirms that uprooting modifies both the intensity and spatial scale of morphodynamic organization. At higher discharges, the reattachment zone lengthens, bar wavelength expands, and the depositional lobe shifts downstream, amplifying the morphodynamic response. The staged removal mimics natural scour-mediated (Type-II) uprooting, providing an experimental framework to interpret flood-induced vegetation loss and its geomorphic impacts. From a practical standpoint, the results offer guidance for river management. Selective (partial) vegetation removal – such as trimming or thinning vegetation patches at the bar during moderate flows – is expected to intensify local scour for roughly 1–2 bar lengths downstream. This approach could be used to maintain navigation channels or prevent aggradation in critical sections. Conversely, complete vegetation removal tends to reset the bar morphology to a shorter-wavelength, free-bar state, which stabilizes bar positions but shifts the bars downstream of their original locations. This distinction provides a process-based framework for selecting vegetation management strategies to achieve a specific geomorphic goal. Future work should test flexible/submerged canopies and varied patch densities under unsteady hydrographs, mixed sediments, and mobile banks, capturing both Type-I (drag) and Type-II (scour-mediated) uprooting. Declarations Acknowledgements / Funding: This study was partially funded by a JSPS Grant-in-Aid for Scientific Research (KAKENHI) (No. 24K07677). Author contributions: Conceptualization: [Saqib Habib, Norio Tanaka], Methodology: [Saqib Habib], Formal analysis and investigation: [Saqib Habib], Visualization: [Saqib Habib], Writing - original draft preparation: [Saqib Habib], Writing - review and editing: [Saqib Habib, Norio Tanaka], Supervision: [Saqib Habib, Norio Tanaka]. Data availability: The data that supports the findings of this study are available on the request from the corresponding author. Conflict of Interest: The authors declare that they have no conflicts of interest. Ethical approval: This article does not contain any studies with human participants or animals performed by any of the authors. Informed consent: Informed consent was obtained from all individual participants included in the study. References Church M, Ferguson R. Morphodynamics: Rivers beyond steady state. Water Resour Res 2015;51:1883–97. https://doi.org/10.1002/2014WR016862. Gurnell AM, Bertoldi W, Corenblit D. Changing River Channels: The Roles of Hydrological Processes, Plants and Pioneer Fluvial Landforms in Humid Temperate, Mixed Load, Gravel Bed Rivers. Earth Sci Rev 2012;111:129–41. https://doi.org/10.1016/j.earscirev.2011.11.006. Corenblit D, Piegay H, Arrignon F, Gonzalez-Sargas E, Bonis A. Interactions between vegetation and river morphodynamics. Part I: Research clarifications and challenges. Earth Sci Rev 2024;253. https://doi.org/10.1016/j.earscirev.2024.104769. Huai W, Li S, Katul GG, Liu M, Yang Z. Flow dynamics and sediment transport in vegetated rivers: A review. Journal of Hydrodynamics 2021;33:400–20. Bejarano MD, Sordo-Ward A, Garrote L, García J. Riparian vegetation metrics as tools for guiding ecological restoration in riverscapes. Knowl Manag Aquat Ecosyst 2011;402:21. https://doi.org/10.1051/kmae/2011075. Gran K, Paola C. Riparian vegetation controls on braided stream dynamics. Water Resour Res 2001;37:3275–83. https://doi.org/10.1029/2000WR000203. Naiman RJ, Decamps H. The ecology of interfaces: riparian zones. Annu Rev Ecol Syst 1997;28:621–58. https://doi.org/10.1146/annurev.ecolsys.28.1.621. Sakio H. Effects of natural disturbance on the regeneration of riparian forests in mountainous regions in Japan. Plant Ecol 1997;132:181–95. https://doi.org/10.1023/A:1009772119318. Merritt DM, Poff NL. Shifting dominance of key drivers of riparian vegetation composition along a prairie-to-montane river network. Ecology 2010;91:1645–58. https://doi.org/10.1890/09-0 shifting. Song U, Kim D, Lee EJ, Balke T, Bouma TJ. Life-History Plasticity of Riparian Annual Plants Adapted to Extreme Variations in Water Level: Mesocosm Experiments. PLoS One 2016;11. https://doi.org/10.1371/journal.pone.0147551. Dixon MD, Turner MG, Naiman RJ. The influence of local and landscape-scale factors on the distribution of pioneer tree seedlings on the Wisconsin River, USA. Ecosystems 2002;5:369–83. https://doi.org/10.1007/s10021-001-0083-9. Tabacchi E, Lambs L, Guilloy H, Planty-Tabacchi AM, Muller E, Decamps H. The role of riparian vegetation in the ecological integrity of alluvial rivers. Freshw Biol 1998;40:609–23. https://doi.org/10.1046/j.1365-2427.1998.00421.x. Kim D, Yu J, Lee S, Kang T, Cho KH. Spatial Distribution of Vegetation on Stream Bars and the Riparian Zone Reflects Successional Pattern Due to Fluid Dynamics of River. Water (Basel) 2023;15:1493. https://doi.org/10.3390/w15081493. Mahoney JM, Rood SB. Streamflow requirements for cottonwood seedling recruitment—an integrative model. Wetlands 1998;18:634–45. https://doi.org/10.1007/BF03161678. Hortobágyi B, Corenblit D, Vautier F, Steiger J, Roussel E. Riparian Vegetation and Sediment Supply on the Morphodynamic Response of an Experimental Stream to Floods. Front Environ Sci 2019;7:40. https://doi.org/10.3389/fenvs.2019.00040. Zhang Y, Wang X, Liu X. Effects of Patch Properties of Submerged Vegetation on Sediment Scouring and Deposition. Water (Basel) 2024;16:2144. https://doi.org/10.3390/w16152144. Calvani G, Francalanci S, Solari L. A Physical Model for the Uprooting of Flexible Vegetation on River Bars. Water Resour Res 2019;55:4674–90. https://doi.org/10.1029/2018WR024268. Yagci O, Celik F, Kitsikoudis V, Koken M. Experimental study on influence of different patterns of an emergent vegetation patch on the flow field and scour/deposition processes in the wake region. Water Resour Res 2023;59. https://doi.org/10.1029/2023WR034978. Wang X, Li S, Yang Z, Huai W. Incipient sediment motion in vegetated open-channel flows predicted by critical flow velocity. Journal of Hydrodynamics 2022;34:63–8. Li S, Huai W, Vyawahare R. Review of the effect of river vegetation on sediment transport and river morphology and erosion prevention. Journal of Hydrodynamics 2025. https://doi.org/10.1007/s42241-024-0065-z. Vannoppen W, vanmaercke M, De Baets S, Poesen J. How do root and soil characteristics affect the erosion-reducing potential of plant species? Plant Soil 2017;419:1–18. https://doi.org/10.1007/s11104-017-3301-4. De Baets S, Poesen J, Gyssels G, Knapen A. Impact of root architecture on the erosion-reducing potential of roots during concentrated flow. Earth Surf Process Landf 2008;33:1323–45. https://doi.org/10.1002/esp.1470. Edmaier K, Burlando P, Perona P. Mechanisms of vegetation uprooting by flow in alluvial non-cohesive sediment. Hydrol Earth Syst Sci 2011;15:1615–27. https://doi.org/10.5194/hess-15-1615-2011. van de Lageweg WI, Veenstra JL, van der Lee GEM, Hulscher SJMH. Processes and parameters underlying the failure of salt marsh vegetation in different sediments. University of Twente; 2022. Perona P, Crouzy B, Molnar P, Dudun A, Vetsch D, Burlando P. Resilience of riverbed vegetation to uprooting by flow. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 2018;474. https://doi.org/10.1098/rspa.2017.0547. Bywater‐Reyes S, Wilcox AC, Stella JC, Lightbody AF. Flow and scour constraints on uprooting of pioneer woody seedlings. Water Resour Res 2015;51:9190–206. Kleinhans MG, McMahon WJ, Davies NS. What even is a meandering river? A philosophy-enhanced synthesis of multilevel causes and systemic interactions contributing to river meandering. Geological Society, London, Special Publications, vol. 540, 2024. https://doi.org/10.1144/SP540-2022-218. Lightbody AF, Kui L, Stella JC, Skorko KW, Bywater-Reyes S, Wilcox AC. Riparian vegetation and sediment supply regulate the morphodynamic response of an experimental stream to floods. Front Environ Sci 2019;7:40. Sidle RC, Ochiai H. Landslides: Processes, Prediction, and Land Use. American Geophysical Union; 2006. https://doi.org/10.1029/GM160. Ohtsuka S, Sato Y, Yoshikawa T, Sugii T, Kodaka T, Maeda K. Levee damage and revetment erosion by the 2019 Typhoon Hagibis in the Chikuma River, Japan. Soils and Foundations 2021;61:1172–88. Calvani G, Francalanci S, Solari L. Insights into the dynamics of vegetated alternate bars by means of flume experiments. Water Resour Res 2023;59. https://doi.org/10.1029/2022WR032536. Geng X, Cao W, Liu C, Zhang G. Experimental Study of Bedform Development Characteristics and Their Effects on Sediment Transport. Applied Sciences 2024;14:9823. Crosato A, Mosselman E, Beidmariam Desta F, Uijttewaal WSJ. Experimental and numerical evidence for intrinsic nonmigrating bars in alluvial channels. Water Resour Res 2011;47. Habib S, Tanaka N. Effect of Vegetation Type and Location on the Change of Alternate Sandbars in a Straight River Channel. International Journal of Civil Engineering 2025. https://doi.org/10.1007/s40999-025-01118-9. Rominger JT, Lightbody AF, Nepf HM. Effects of added vegetation on sand bar stability and stream hydrodynamics. Journal of Hydraulic Engineering 2010;136:994–1002. Zong L, Nepf H. Spatial distribution of deposition within a patch of vegetation. Water Resour Res 2011;47. KUROKI M, KISHI T. Regime criteria on bars and braids in alluvial straight channels. Proceedings of the Japan Society of Civil Engineers, vol. 1984, Japan Society of Civil Engineers; 1984, p. 87–96. Wong M, Parker G. Reanalysis and correction of bed-load relation of Meyer-Peter and Müller using their own database. Journal of Hydraulic Engineering 2006;132:1159–68. Lanzoni S. Experiments on bar formation in a straight flume: 2. Graded sediment. Water Resour Res 2000;36:3351–63. Kleinhans MG, van Dijk WM, van de Lageweg WI, Hoyal DCJD, Markies H, van Maarseveen M, et al. Quantifiable effectiveness of experimental scaling of river- and delta morphodynamics and stratigraphy. Earth Sci Rev 2014;133:43–61. https://doi.org/10.1016/j.earscirev.2014.03.001. Shahmohammadi R, Afzalimehr H, Sui J. Assessment of critical shear stress and threshold velocity in shallow flow with sand particles. Water (Basel) 2021;13:994. Postma G, Kleinhans MG, Meijer PT, Eggenhuisen JT. Sediment transport in analogue flume models compared with real‐world sedimentary systems: A new look at scaling evolution of sedimentary systems in a flume. Sedimentology 2008;55:1541–57. Redolfi M, Welber M, Carlin M, Tubino M, Bertoldi W. Morphometric properties of alternate bars and water discharge: A laboratory investigation. Earth Surface Dynamics 2020;8:789–808. https://doi.org/10.5194/esurf-8-789-2020. Crosato A, Mosselman E. Simple physics-based predictor for the number of river bars and the transition between meandering and braiding. Water Resour Res 2009;45. https://doi.org/10.1029/2008WR007242. Zong L, Nepf H. Spatial distribution of deposition within a patch of vegetation. Water Resour Res 2011;47. https://doi.org/10.1029/2010WR009516. Bywater-Reyes S, Diehl RM, Wilcox AC. The influence of a vegetated bar on channel-bend flow dynamics. Earth Surface Dynamics 2018;6:487–503. https://doi.org/10.5194/esurf-6-487-2018. Gong M, Wu G, Du S. Laboratory Study of Local Scour Around an Array of Pile Groups in Clear-Water Scour Conditions. J Mar Sci Eng 2025;13:137. https://doi.org/10.3390/jmse13010137. Yagci O, Özgur Kirca VS, Kitsikoudis V, Wilson CAME, Celik MF, Sertkan C. Experimental study on influence of different patterns of an emergent vegetation patch on the flow field and scour/deposition processes in the wake region. Water Resour Res 2024;60:e2023WR034978. Wickramasinghe R, Tanaka N. Investigation of hydrodynamics along an embankment generated by a nearby riparian vegetation patch. Landscape and Ecological Engineering 2023;19:179–97. Smith RD, Sidle RC, Porter PE, Noel JR. Effects of experimental removal of woody debris on the channel morphology of a forest, gravel-bed stream. J Hydrol (Amst) 1993;152:153–78. Redolfi M, Musa M, Guala M. On steady alternate bars forced by a localized asymmetric drag distribution in erodible channels. J Fluid Mech 2021;916. https://doi.org/10.1017/jfm.2021.122. Caroppi G, Västilä K, Järvelä J, Lee C, Ji U, Kim HS, et al. Flow and wake characteristics associated with riparian vegetation patches: Results from field‐scale experiments. Hydrol Process 2022;36:e14506. Montgomery DR, Buffington JM. Channel-reach morphology in mountain drainage basins. Geol Soc Am Bull 1997;109:596–611. Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 30 Oct, 2025 Reviewers invited by journal 30 Oct, 2025 Editor assigned by journal 29 Oct, 2025 First submitted to journal 26 Oct, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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\u003cstrong\u003e(c) \u003c/strong\u003eSchematic of the staggered arrangement of the vegetation cylinders. Parameter \u003cem\u003eD\u003c/em\u003e represents the cylinder diameter, i.e., 0.004 m, \u003cem\u003eG\u003c/em\u003e represents the clear spacing between cylinders, 0.0086 m, and \u003cem\u003ed\u003c/em\u003e is the center-to-center distance between cylinders, across the flow direction, 0.0256 m. The relative spacing (\u003cem\u003eG/D\u003c/em\u003e) was set to 2.2; \u003cstrong\u003e(d) \u003c/strong\u003eExperimental setup showing emergent rigid vegetation cylinders in a sediment bed (10 cm thick), with vegetation height ℎ\u003csub\u003ev\u003c/sub\u003e, flow depth ℎ\u003cstrong\u003e.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7909292/v1/ecb366ad00d3f903f106fdb3.png"},{"id":95656095,"identity":"41e8434b-b36f-4ad6-969b-a48f39661e74","added_by":"auto","created_at":"2025-11-11 16:17:45","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":465279,"visible":true,"origin":"","legend":"\u003cp\u003eStaged-removal and a conceptual hydrodynamic diagram; \u003cstrong\u003e(a, a’)\u003c/strong\u003e Fully vegetated (V\u003csub\u003eus\u003c/sub\u003e), \u003cstrong\u003e(b, b’)\u003c/strong\u003e partial leading-edge retreat (\u003cem\u003el\u003c/em\u003e\u003csub\u003e\u003cem\u003ex1\u003c/em\u003e\u003c/sub\u003e=0.2 m) (V\u003csub\u003eur1\u003c/sub\u003e); \u003cstrong\u003e(c, c’)\u003c/strong\u003e bare-bed condition after complete removal (\u003cem\u003el\u003c/em\u003e\u003csub\u003e\u003cem\u003ex2\u003c/em\u003e\u003c/sub\u003e=0.4 m) (V\u003csub\u003eur2\u003c/sub\u003e). Here, V\u003csub\u003eus\u003c/sub\u003e: upstream vegetation, V\u003csub\u003eur\u003c/sub\u003e: vegetation removal.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7909292/v1/11cefd0cd7e7f147f7216b3d.png"},{"id":95586441,"identity":"6f68cc83-c07b-4304-8e2a-8afff83093b9","added_by":"auto","created_at":"2025-11-10 23:52:58","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":781970,"visible":true,"origin":"","legend":"\u003cp\u003eContour maps of bed elevation (\u003cem\u003ez\u003c/em\u003e) and Bed elevation changes (\u003cem\u003e∆z\u003c/em\u003e) for \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e: \u003cstrong\u003e(a)\u003c/strong\u003e Case 1-NN, \u003cstrong\u003e(b)\u003c/strong\u003e Case1-V\u003csub\u003eus\u003c/sub\u003e, \u003cstrong\u003e(c)\u003c/strong\u003e Case1-V\u003csub\u003eur1\u003c/sub\u003e after 1 hour of Stage 1, \u003cstrong\u003e(d)\u003c/strong\u003e Case1-V\u003csub\u003eur1\u003c/sub\u003e after 4 hours of Stage 1, \u003cstrong\u003e(e)\u003c/strong\u003e Case1-V\u003csub\u003eur2 \u003c/sub\u003eafter 1 hour of Stage 2, \u003cstrong\u003e(f)\u003c/strong\u003e Case1-V\u003csub\u003eur2 \u003c/sub\u003eafter 6 hours of Stage 2. Here, V\u003csub\u003eus\u003c/sub\u003e (Upstream vegetation), V\u003csub\u003eur\u003c/sub\u003e (Vegetation uprooting), L1 (patch-front), L2 (inside-patch), L3 (lee-side wake), and L4 (opposite-bank bar/crest). Subscripts indicate time within the uprooting bed measurement sequence: i and j for Stage-1 (partial/leading-edge cut) within the stage, and k and l for Stage-2 (complete removal) for \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-7909292/v1/f7f8b61d43c63b5fe3d8c447.png"},{"id":95586445,"identity":"583f5456-b42a-43e0-b602-fa4dfac6b932","added_by":"auto","created_at":"2025-11-10 23:52:58","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":782397,"visible":true,"origin":"","legend":"\u003cp\u003eContour maps of bed elevation (\u003cem\u003ez\u003c/em\u003e) and Bed elevation changes (\u003cem\u003e∆z\u003c/em\u003e) for \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e: \u003cstrong\u003e(a)\u003c/strong\u003e Case 2-NN, \u003cstrong\u003e(b)\u003c/strong\u003e Case2-V\u003csub\u003eus\u003c/sub\u003e, \u003cstrong\u003e(c)\u003c/strong\u003e Case2-V\u003csub\u003eur1\u003c/sub\u003e after 1 hour of Stage 1, \u003cstrong\u003e(d)\u003c/strong\u003e Case2-V\u003csub\u003eur1\u003c/sub\u003e after 4 hours of Stage 1, \u003cstrong\u003e(e)\u003c/strong\u003e Case2-V\u003csub\u003eur2\u003c/sub\u003e after 1 hour of Stage 1, \u003cstrong\u003e(f)\u003c/strong\u003e Case2-V\u003csub\u003eur2\u003c/sub\u003e after 5 hours of Stage 1. Here, V\u003csub\u003eus\u003c/sub\u003e (Upstream vegetation), V\u003csub\u003eur\u003c/sub\u003e (Vegetation uprooting), L1 (patch-front), L2 (inside-patch), L3 (lee-side wake), and L4 (opposite-bank bar/crest). Subscripts indicate time within the uprooting bed measurement sequence: i and j for Stage-1 (partial/leading-edge cut) within the stage, and k and l for Stage-2 (complete removal) for \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-7909292/v1/c2e4131106912e7e503c3410.png"},{"id":95656155,"identity":"e60dca25-9e79-4c40-9ec0-330594e17f4d","added_by":"auto","created_at":"2025-11-11 16:17:53","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":242369,"visible":true,"origin":"","legend":"\u003cp\u003eContour Map of bed elevation (\u003cem\u003ez\u003c/em\u003e), showing the equilibrium channel morphology of complete vegetation removal (\u003cstrong\u003ea)\u003c/strong\u003e Case 1, \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e=0.0025 m\u003csup\u003e3\u003c/sup\u003e/s, and \u003cstrong\u003e(b)\u003c/strong\u003e Case 2, \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e=0.003 m\u003csup\u003e3\u003c/sup\u003e/s.\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-7909292/v1/c05fbd4b4a4ea571fe0d3db1.png"},{"id":95586451,"identity":"7e3dde6c-4153-4308-aecd-685b85d2012b","added_by":"auto","created_at":"2025-11-10 23:52:58","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":519666,"visible":true,"origin":"","legend":"\u003cp\u003eCross-sections of normalized bed change (\u003cem\u003eΔz/h\u003c/em\u003e) at three patch (P1)-aligned transects (L1, L2 and L3) comparing V\u003csub\u003eus\u003c/sub\u003e, V\u003csub\u003eur1\u003c/sub\u003e (i, j), and V\u003csub\u003eur2\u003c/sub\u003e (k, l): \u003cstrong\u003e(a)\u003c/strong\u003e Case 1: L1 (leading edge), \u003cstrong\u003e(b)\u003c/strong\u003e Case1: L2 (patch interior), \u003cstrong\u003e(c)\u003c/strong\u003e Case 1: L3 (lee axis), \u003cstrong\u003e(d)\u003c/strong\u003e Case 2: L1 (leading edge), \u003cstrong\u003e(e)\u003c/strong\u003e Case 2: L2 (patch interior), \u003cstrong\u003e(f)\u003c/strong\u003e Case 3: L3 (lee axis). Here, i, j, k, and l represent the bed cross-section at various hours.\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-7909292/v1/2f81eaca11e9ee62c55835e8.png"},{"id":95656206,"identity":"b0d34e8a-985b-4ffa-a529-5a2094fc9d53","added_by":"auto","created_at":"2025-11-11 16:18:01","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":498777,"visible":true,"origin":"","legend":"\u003cp\u003eNormalized morphometrics summarizing planform: \u003cstrong\u003e(a)\u003c/strong\u003e Areal Fractions of deposition and scour (\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e, \u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₋\u003c/em\u003e\u003c/sup\u003e), \u003cstrong\u003e(b)\u003c/strong\u003e Volume-Balanced Shares (\u003cem\u003eΦ⁺, Φ⁻\u003c/em\u003e) \u003cstrong\u003e(c)\u003c/strong\u003e Planform Asymmetry Index (\u003cem\u003ePAIₕ\u003c/em\u003e), and \u003cstrong\u003e(d)\u003c/strong\u003e Right-Bank Share of Deposition (\u003cem\u003eSᵣ\u003c/em\u003e). Here, P means vegetation patch. These results show that uprooting initiates a self-balancing process that redistributes sediment both laterally and longitudinally until a quasi-equilibrium bar configuration emerges.\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-7909292/v1/8645d6d77b30c51f3eca62ed.png"},{"id":95586452,"identity":"e405b0ec-bf30-491d-abe0-6286564b2717","added_by":"auto","created_at":"2025-11-10 23:52:58","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":276633,"visible":true,"origin":"","legend":"\u003cp\u003eNormalized morphometrics summarizing planform metrics for three distinct vegetation patch locations (P1, P2, P3) along the flume for discharges \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e and \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e \u003cstrong\u003e(a)\u003c/strong\u003e Areal Fractions of Deposition and Scour (\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e, \u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₋\u003c/em\u003e\u003c/sup\u003e), \u003cstrong\u003e(b)\u003c/strong\u003e Planform Asymmetry Index (\u003cem\u003ePAIₕ\u003c/em\u003e). Here, P means vegetation patch.\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-7909292/v1/f62c4a760bdf43a0cfa0a0ca.png"},{"id":95655524,"identity":"c6ef0b47-f270-40da-a7c5-373177f5c759","added_by":"auto","created_at":"2025-11-11 16:16:23","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":224686,"visible":true,"origin":"","legend":"\u003cp\u003eLongitudinal thalweg profiles of Δz/h and derived bar wavelength (λ) for \u003cstrong\u003e(a)\u003c/strong\u003e \u003cem\u003eQ₁\u003c/em\u003e and \u003cstrong\u003e(b)\u003c/strong\u003e \u003cem\u003eQ₂\u003c/em\u003e across Phase 1 (alternate bars), V\u003csub\u003eus\u003c/sub\u003e, V\u003csub\u003eur1\u003c/sub\u003e, and V\u003csub\u003eur2\u003c/sub\u003e. This demonstrates that vegetation removal not only reorganizes scour and deposition locally but also governs the broader rhythm of bar spacing and propagation, linking patch-scale disturbance to reach-scale morphodynamics.\u003c/p\u003e","description":"","filename":"floatimage12.png","url":"https://assets-eu.researchsquare.com/files/rs-7909292/v1/21c40daf53c01f931548c3c4.png"},{"id":95818669,"identity":"6769a18a-3082-4f5a-a4a3-86a8ab47cbdc","added_by":"auto","created_at":"2025-11-13 10:27:53","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":7371340,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7909292/v1/c9745a2c-d057-4912-a498-4b019f1b4816.pdf"}],"financialInterests":"","formattedTitle":"A Nonlinear State Shift: Morphodynamic Thresholds During Progressive Vegetation Uprooting on Alternate Bars","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eOver recent decades, river science has shifted from a static, discipline-fragmented view to a unified biomorphodynamic framework [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Traditionally, morphology was analyzed using classical mechanics with equilibrium emphasis and separate geologic/hydrologic/biologic influences [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Accumulating evidence shows this is inadequate for natural complexity; instead, a biomorphodynamic perspective recognizes reciprocal interactions among flow, sediment, and vegetation as a single system [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Recent synthesis shows that emergent, submerged, and flexible canopies systematically modify turbulence, shear, dispersion, and sediment transport, driving bar-scale adjustments and channel-pattern shifts in vegetated rivers [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eWithin this framework, riparian vegetation is a powerful geomorphic agent: plants increase hydraulic roughness, promote sedimentation, and stabilize banks via roots [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. These reciprocal plant\u0026ndash;flow\u0026ndash;sediment interactions have significant implications for management and restoration [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. The practical impact of this feedback is substantial for river management and restoration. For example, dams reduce flood frequency/magnitude [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], enable vegetation encroachment on bars and floodplains, stabilize surfaces, and potentially shift channels from braided to meandering patterns\u0026mdash;altering capacity and habitat [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eColonization of bare alluvial surfaces (e.g., nascent sandbars) by pioneer species initiates biogeomorphic succession\u0026mdash;co-evolution of landforms and plant communities [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Pioneer traits include prolific, easily dispersed propagules (\u0026ldquo;invader\u0026rdquo;), rapid growth, and tolerance of drought or temporary flooding [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Many riparian pioneers, such as willows (\u003cem\u003eSalix\u003c/em\u003e spp.) and cottonwoods (\u003cem\u003ePopulus\u003c/em\u003e spp.), show remarkable life-history plasticity; for example, they can resprout after being broken or buried by sediment (an \"endurer\" strategy) and withstand prolonged flooding (a \"resister\" strategy) [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. This adaptability is essential for survival in dynamic river environments, where conditions can change quickly with each flow event [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eVegetation establishment on sandbars depends on hydrogeomorphic factors across scales [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. At the broad landscape scale, the river's flow regime is the primary driver [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. At the landscape scale, the flow regime controls when/where moist bare sediment becomes available. This creates a \u0026ldquo;recruitment box\u0026rdquo;: many pioneers synchronize dispersal/germination with the spring-flood recession, exposing nursery sites [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Within bars, elevation, substrate texture, and soil moisture are critical [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]; higher, less-scoured surfaces and finer (silt/sand) substrates that retain moisture favor first-season roots [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eOnce established, vegetation becomes an ecosystem engineer, altering local hydraulics and morphology [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Emergent plants increase hydraulic roughness, creating zones of reduced flow velocity and lower bed shear stress [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. This localized deceleration promotes sediment deposition, enabling vegetated sandbars to grow larger, higher, and more stable than unvegetated counterparts [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Effects scale with stem density, patch extent, and permeability [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. At the grain scale, incipient sediment motion in vegetated open-channel flow can be predicted using a critical depth-averaged velocity; notably, the derived threshold decreases as vegetation density increases [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe geomorphic influence of vegetation extends below the surface, where plant roots mechanically reinforce sediment [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. The type of erosion protection provided is closely linked to the plant's root architecture. Fibrous systems (grasses/sedges) form shallow root mats that resist surface erosion in low-energy flows, whereas deeper, rigid taproots (woody plants) resist deeper scour and mass failure during high-energy floods [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Hence, landform stability depends on the collective root architecture relative to river erosional forces.\u003c/p\u003e\u003cp\u003eAlthough vegetation enhances geomorphic stability, extreme floods can remove even well-established plants. Accurately predicting the resilience of vegetated landforms requires an understanding of two primary uprooting mechanisms, which differ based on plant development and sediment erosion [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. The first type, Type I uprooting, is a Drag-induced failure that occurs instantaneously when hydrodynamic forces on the stem and leaves surpass the root system\u0026rsquo;s anchoring strength. This process primarily affects young, shallowly rooted seedlings [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. In contrast, Type II uprooting is a Scour-mediated failure, typically affecting established vegetation with stronger roots. Drag force alone does not suffice; instead, removal occurs gradually as localized scour erodes sediment from the root mass, weakening anchorage until a threshold is reached [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Such scour is often accelerated by powerful horseshoe vortices forming at the patch\u0026rsquo;s upstream edge, resulting in trench-like erosion patterns and higher vulnerability for plants near this edge [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eRemoval of riparian vegetation\u0026mdash;by natural uprooting or deliberate clearing\u0026mdash;can produce long-lasting morphological change. Without vegetative stabilization, channels are prone to increased bank erosion and widening and may shift from single- to multi-thread patterns [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Vegetation clearing can cause unintended channel enlargement through loss of root cohesion [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Over time, the decay of roots after vegetation loss further reduces slope stability and increases susceptibility to failure [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. This weakening may produce preconditioned landforms for catastrophic collapse during major floods. At Japan\u0026rsquo;s Chikuma River Bridge, an unvegetated, non-cohesive sandbar was eroded entirely during Typhoon Hagibis (2019) [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], contributing to severe levee damage.\u003c/p\u003e\u003cp\u003eWhile the end-states of fully vegetated vs. bare channels are well documented, the transient morphodynamic pathway between them\u0026mdash;especially the response of alternate bars to progressive, partial removal\u0026mdash;remains poorly understood [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Prior work emphasizes end-members or seedling-scale mechanics, overlooking meso-scale dynamics during patch degradation. This issue is not merely academic. Removing a leading edge transforms a sheltered wake into an exposed erosional front. Assuming linear responses to partial clearing risks design errors in management/restoration. Quantifying morphodynamic adjustments during these transient stages is therefore a critical, unresolved challenge.\u003c/p\u003e\u003cp\u003eTo address this challenge, this study uses a controlled flume experiment to quantify (1) the morphodynamic response of alternate bar topography to the progressive, staged removal of a vegetation patch, and (2) track the evolution of scour/deposition around and within the patch using quantitative morphodynamic metrics. These objectives elucidate the progression from vegetated to bare states, informing management/restoration.\u003c/p\u003e"},{"header":"2. METHODOLOGY","content":"\u003cp\u003eThis study was conducted using a multi-phase laboratory flume experiment designed to systematically examine the morphodynamic response of alternate sandbars to the establishment and progressive removal of vegetation. The experimental program comprised three phases: (1) creation of a stable, non-migrating alternate bar system as a geomorphic baseline, (2) establishment of vegetation on these bars till morphological equilibrium was reached, and (3) successive staged removal of vegetation to simulate gradual uprooting and assess the associated transient, nonlinear morphological adjustments.\u003c/p\u003e\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Experimental facility, setup and materials\u003c/h2\u003e\u003cp\u003eExperiments were performed in a rectangular flume measuring 15 m in length, 0.5 m in width, and 0.5 m in depth at Saitama University in Japan. The flume\u0026rsquo;s transparent glass sidewalls allowed direct flow visualization and bedform observation. A closed-circuit pump maintained a constant water discharge, monitored at the downstream triangular V-notch weir (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a)).\u003c/p\u003e\u003cp\u003eThe movable bed consisted of a 0.1 m thick layer of uniform, non-cohesive quartz sand with a median grain size (\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003e50\u003c/em\u003e\u003c/sub\u003e) of 0.875 mm and a density (\u003cem\u003eρ\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e) of 2,650 kg/m\u0026sup3;. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the sediment and experimental hydraulic parameters. Recent literature confirms that sand in this size range transition directly from plane bed to dunes under the hydraulic conditions applied in this study [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eSediment and Hydraulic Parameters\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"7\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eParameter\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eSymbol\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eUnit\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e\u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"7\" nameend=\"c7\" namest=\"c1\"\u003e\u003cp\u003eSediment Properties\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cb\u003eMaterial\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"6\" nameend=\"c7\" namest=\"c2\"\u003e\u003cp\u003eUniform, non-cohesive quartz sand\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMedian Grain Size\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e\u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003e50\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003emm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e\u003cp\u003e0.875\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFluid Density\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e\u003cem\u003eρ\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003ekg/m\u0026sup3;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e\u003cp\u003e1,000\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSediment Density\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e\u003cem\u003eρ\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003ekg/m\u0026sup3;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e\u003cp\u003e2,650\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSediment Influx**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003e\u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003eb\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003ekg/s\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.0033\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003e0.00145\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"7\" nameend=\"c7\" namest=\"c1\"\u003e\u003cp\u003e\u003cb\u003eHydraulic Conditions\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInitial Bed Slope*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003es\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003em/m\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e\u003cp\u003e1/200\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDischarge\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eQ\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003em\u0026sup3;/s\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e0.0025\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.003\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInitial Water Depth*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eh\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003ecm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e1.45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e1.75\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFroude Number**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eFr\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e0.91\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.83\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eShields Parameter**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eϑ\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e0.050\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.061\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRun Time (Phase I, Phase III)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003ehour\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e\u003cp\u003e6\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRun Time (Phase II)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e\u003cp\u003ehour\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c7\" namest=\"c5\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"7\"\u003e\u003cb\u003eNote\u003c/b\u003e: \u003csup\u003e\u003cb\u003e*\u003c/b\u003e\u003c/sup\u003eMeasured along the center of the channel, \u003cb\u003e**\u003c/b\u003ecalculated using the equations for the initial settings for sandbar formation, denominators \u003csub\u003e1\u003c/sub\u003e and \u003csub\u003e2\u003c/sub\u003e represent the discharge \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e parameters, respectively.\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eAt the flume inlet, a 0.1 m wide transverse block along the left channel wall created a steady hydraulic perturbation that generated a stationary alternate bar (\u003cem\u003em\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1) downstream, as shown in the schematic diagram in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(b). This hydraulic forcing method is a well-established technique for generating a stationary bar, providing a stable geomorphic template for systematically examining the effects of vegetation [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e\u003cp\u003ePioneer vegetation was simulated using rigid wooden cylinders with a diameter of 4 mm and a height of 0.18 m, in a fully emergent condition. Following the prior experimental model [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] pioneer vegetation species such as willow (\u003cem\u003eSalix\u003c/em\u003e spp.) were scaled at a 1:50 geometric scale, corresponding to a typical trunk diameter of ~\u0026thinsp;0.2 m in the field. Cylinders were arranged in a dense staggered pattern (relative spacing \u003cem\u003eG/D\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.2; \u003cem\u003eG\u003c/em\u003e\u0026thinsp;=\u0026thinsp;clear spacing between cylinders) to form a semicircular patch 0.3 m in radius, positioned on the sandbar apex facing the flow (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(c); Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e: vegetation patch characteristics). Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(d) shows the physical installation of emergent cylinders on the 0.1 m sand layer. These details address patch porosity and frontal obstruction, which are used later to interpret wake deposition and edge scour. Although rigid cylinders do not capture the flexibility of natural plants, they are a widely accepted proxy for reproducing the bulk hydraulic resistance and flow obstruction effects of vegetation in laboratory experiments [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eCharacteristics of Simulated Emergent Vegetation Patch\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eParameter\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eSymbol\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eValue\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eUnit\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"1\" nameend=\"c5\" namest=\"c5\"\u003e\u0026nbsp;\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e\u003cp\u003eScaled vegetation cylinder\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMaterial\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e\u003cp\u003eRigid wooden cylinders\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c5\" namest=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDiameter\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eD\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003emm\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c5\" namest=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHeight\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eh\u003c/em\u003e\u003csub\u003e\u003cem\u003ev\u003c/em\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003em\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c5\" namest=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e\u003cp\u003eScaling and Arrangement\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGeometric Scale\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e1:50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c5\" namest=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEquivalent Field Trunk Diameter\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e~\u0026thinsp;0.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003em\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c5\" namest=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eArrangement Pattern\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eStaggered\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c5\" namest=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRelative Spacing\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eG\u003c/em\u003e/\u003cem\u003eD\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2.2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c5\" namest=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colspan=\"5\" nameend=\"c5\" namest=\"c1\"\u003e\u003cp\u003e\u003cb\u003ePatch Geometry\u003c/b\u003e\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eShape\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"3\" nameend=\"c4\" namest=\"c2\"\u003e\u003cp\u003eSemicircular\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c5\" namest=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eRadius\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e0.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003em\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"1\" nameend=\"c5\" namest=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThis study focuses on morphodynamics under low-flow, subcritical hydraulic conditions, which are representative of the periods during which vegetation is established and stabilized. While high-flow events generate bare surfaces, stabilization and vegetation colonization predominantly occur during subsequent low-flow phases. Therefore, experiments were conducted under subcritical flow with Froude number (\u003cem\u003eFr)\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;1.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Experimental procedure\u003c/h2\u003e\u003cp\u003eThe initial experimental phase aimed at creating a stable, non-migrating alternate bar serving as a baseline geomorphic reference. Hydraulic parameters were selected based on established regime diagrams for alternate bar formation [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. The procedure began with a sand bed flattened to an initial slope (\u003cem\u003es\u003c/em\u003e) of 1/200. The experiment was conducted on two flow cases to bracket low flow morphodynamics: \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.0025 m\u0026sup3; s⁻\u0026sup1; and \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.003 m\u0026sup3; s⁻\u0026sup1;. The initial water depths were \u003cem\u003eh₁\u003c/em\u003e\u0026asymp;1.45 cm and \u003cem\u003eh₂\u003c/em\u003e\u0026asymp;1.75 cm, yielding \u003cem\u003eFr\u003c/em\u003e\u0026thinsp;≲\u0026thinsp;0.9. Sediment was fed at the inlet at a rate calculated to match the channel's transport capacity for Phase I only [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e], thereby preventing net bed aggradation or degradation. The system reached dynamic equilibrium under subcritical flow conditions (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe Shields parameter is a dimensionless number that represents the ratio of the fluid force on a sediment particle to the gravitational force acting on it. It is defined in Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e below. The corresponding Shields parameter (\u003cem\u003eθ\u003c/em\u003e), which determines when sediment begins to move, was above the critical threshold for motion (\u003cem\u003eθ\u003c/em\u003e\u003csub\u003e\u003cem\u003ecr\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;0.047), confirming active bedload transport and morphological development. The run continued for five hours until the system reached dynamic equilibrium, defined as the point where the time-averaged bed slope equaled the water surface slope [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e].\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:\\theta\\:=\\frac{\\tau\\:}{\\left(\\left(\\rho\\:-{\\rho\\:}_{s}\\right)g{d}_{50}\\right)}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003ewhere \u003cem\u003eτ\u003c/em\u003e (N/m\u0026sup2;) is the bed shear stress, \u003cem\u003eρ\u003c/em\u003e and \u003cem\u003eρ\u003c/em\u003e\u003csub\u003e\u003cem\u003es\u003c/em\u003e\u003c/sub\u003e are the fluid and sediment densities (kg/m\u0026sup3;), respectively, \u003cem\u003eg\u003c/em\u003e (in m/s\u0026sup2;) is gravitational acceleration, and \u003cem\u003ed\u003c/em\u003e\u003csub\u003e\u003cem\u003e50\u003c/em\u003e\u003c/sub\u003e (mm) is the median grain size.\u003c/p\u003e\u003cp\u003ePhase II established a stable vegetated topography. The full semicircular vegetation patch was installed on the apex of the alternate bar formed during Phase I. Clear water scour conditions were applied by maintaining the same flow discharge without sediment feed, ensuring that sediment redistribution around the vegetation patch was due solely to local scour and deposition rather than additional sediment input. The run lasted 4 hours, allowing scour-deposition patterns to stabilize, thus creating the initial condition for disturbance experiments.\u003c/p\u003e\u003cp\u003eIn Phase III, the transient response of the sandbar was quantified using a two-stage, asymmetric vegetation removal protocol designed to investigate non-linear system responses and potential threshold behaviors. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e illustrates the staged removal sequence: (a, a\u0026rsquo;) fully vegetated baseline (V\u003csub\u003eus\u003c/sub\u003e); (b, b\u0026rsquo;) partial leading-edge retreat (V\u003csub\u003eur1\u003c/sub\u003e); (c, c\u0026rsquo;) complete removal (V\u003csub\u003eur2\u003c/sub\u003e), establishing the bare-patch control for transient comparisons. To capture the transient morphodynamic response, a two-stage removal was applied. In Stage 1, an upstream strip of vegetation (\u003cem\u003el\u003c/em\u003e\u003csub\u003e\u003cem\u003ex1\u003c/em\u003e\u003c/sub\u003e =0.2 m, representing\u0026thinsp;\u0026asymp;\u0026thinsp;30% of the patch cover) was removed. In Stage 2, the remainder of the patch (\u003cem\u003el\u003c/em\u003e\u003csub\u003e\u003cem\u003ex2\u003c/em\u003e\u003c/sub\u003e=0.4 m) was removed. The system was allowed to equilibrate for 4 to 6 hours after each stage. Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the Experimental cases and staged removal protocol.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eExperimental Cases and Staged Removal Protocol\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDischarge\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCase\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eExperimental Phase\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eVegetation Cover\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eUprooting Length (\u003cem\u003el\u003c/em\u003e\u003csub\u003e\u003cem\u003ex\u003c/em\u003e\u003c/sub\u003e)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"5\" rowspan=\"6\"\u003e\u003cp\u003e\u003cem\u003eQ\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCase1-NN\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePhase I\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCase1-V\u003csub\u003eus\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePhase II\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e100%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCase1-V\u003csub\u003eur1\u003c/sub\u003e-i\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePhase III - Stage 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e30%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.2 m\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCase1-V\u003csub\u003eur1\u003c/sub\u003e-j\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePhase III - Stage 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e30%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.2 m\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCase1-V\u003csub\u003eur2\u003c/sub\u003e-k\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePhase III - Stage 2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.4 m\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCase1-V\u003csub\u003eur2\u003c/sub\u003e-l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePhase III - Stage 2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.4 m\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"5\" rowspan=\"6\"\u003e\u003cp\u003e\u003cem\u003eQ\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCase2-NN\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePhase I\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCase2-V\u003csub\u003eus\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePhase II\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e100%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCase2-V\u003csub\u003eur1\u003c/sub\u003e-i\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePhase III - Stage 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e30%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.2 m\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCase2-V\u003csub\u003eur1\u003c/sub\u003e-j\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePhase III - Stage 1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e30%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.2 m\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCase2-V\u003csub\u003eur2\u003c/sub\u003e-k\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePhase III - Stage 2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.4 m\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eCase2-V\u003csub\u003eur2\u003c/sub\u003e-l\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePhase III - Stage 2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e0.4 m\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003cb\u003eNote\u003c/b\u003e: The semicircular patch radius is 0.3 m (centerline chord\u0026thinsp;\u0026asymp;\u0026thinsp;0.6 m). Stage-1 removes the leading 0.2 m; Stage-2 removes the remaining 0.4 m (full clearance). Note, NN: un-vegetated bars (Phase I); V\u003csub\u003eus\u003c/sub\u003e: Upstream Vegetation; V\u003csub\u003eur\u003c/sub\u003e: Vegetation uprooting, i and j correspond to 1 hour and 4 hours of Stage-1 (V\u003csub\u003eur1\u003c/sub\u003e), and k and l to 1 hour and 5 to 6 hours of Stage-2 (V\u003csub\u003eur2\u003c/sub\u003e)\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Measurements and Morphodynamic Analysis Metrics\u003c/h2\u003e\u003cp\u003eLongitudinal water-surface and bed profiles were measured along the thalweg with a rail-mounted point gauge (\u0026plusmn;\u0026thinsp;0.1 mm), sampled every 0.5 m to compute average slopes. To preserve bedform geometry after each phase, the flume was slowly drained after equilibrium. Time subscripts in planform and cross-section plots denote within-stage snapshots: i and j correspond to 1 hour and 4 hours of Stage-1 (V\u003csub\u003eur1\u003c/sub\u003e), and k and l to 1 hour and 5 to 6 hours of Stage-2 (V\u003csub\u003eur2\u003c/sub\u003e). Locations L1\u0026ndash;L4 mark the patch front, interior, lee axis, and opposite-bank bar, respectively.\u003c/p\u003e\u003cp\u003eThe 12-m study reach (2\u0026ndash;14 m) was scanned with a rail-mounted, non-contact 2-D laser profiler (LJ-V-7000, Keyence). Elevation data were acquired at 10 cm longitudinal and 2.28 cm transverse spacing, then processed with a custom FORTRAN algorithm to quantify scour and deposition patterns.\u003c/p\u003e\u003cp\u003eBed change is expressed as depth-normalized relief (Δ\u003cem\u003ez\u003c/em\u003e/\u003cem\u003eh\u003c/em\u003e), where \u003cem\u003eh\u003c/em\u003e is the water depth. Four morphodynamic metrics were derived to describe: (i) Areal fractions (\u003cem\u003eF\u003c/em\u003e), (ii) Planform asymmetry index (\u003cem\u003ePAI\u003c/em\u003e\u003csub\u003e\u003cem\u003eh\u003c/em\u003e\u003c/sub\u003e), (iii) bank-wise deposition (\u003cem\u003eS\u003c/em\u003e\u003csub\u003e\u003cem\u003er\u003c/em\u003e\u003c/sub\u003e), and (iv) volumetric dominance (\u003cem\u003eΦ\u003c/em\u003e) responses (Eqs.\u0026nbsp;\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Equ5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eAreal fractions (\u003cem\u003eF)\u003c/em\u003e are an areal measure of bed change. It is separated into F\u003csup\u003e₊\u003c/sup\u003e and F\u003csup\u003e₋\u003c/sup\u003e, which represent the fraction of the total bed area (\u003cem\u003eA\u003c/em\u003e\u003csub\u003e\u003cem\u003etotal\u003c/em\u003e\u003c/sub\u003e) that experienced aggradation (\u003cem\u003eΔz\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0) and degradation (\u003cem\u003eΔz\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0), respectively (see Eq.\u0026nbsp;\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This metric captures the extent of deposition vs. erosion, independent of the magnitude of elevation change.\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:{F}^{+}=(\\text{A}\\text{r}\\text{e}\\text{a}\\:\\text{w}\\text{h}\\text{e}\\text{r}\\text{e}\\:{\\Delta\\:}\\text{z}\u0026gt;0)/{A}_{total}\\:\\text{a}\\text{n}\\text{d}\\:{F}^{-}=(\\text{A}\\text{r}\\text{e}\\text{a}\\:\\text{w}\\text{h}\\text{e}\\text{r}\\text{e}\\:{\\Delta\\:}\\text{z}\u0026lt;0)/{A}_{total}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003ePlanform asymmetry index normalized by \u003cem\u003eh\u003c/em\u003e (\u003cem\u003ePAIₕ\u003c/em\u003e) metric (see Eq.\u0026nbsp;\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). This metric cleanly captures any flip in lateral dominance after vegetation uprooting and serves as a scalar indicator of bar re-phasing.\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:{PAI}_{ₕ}=\\frac{\\left({⟨\\varDelta\\:z⟩}_{R}-\\:{⟨\\varDelta\\:z⟩}_{L}\\right)}{h}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eTo compute \u003cem\u003ePAI\u003c/em\u003e\u003csub\u003e\u003cem\u003eh\u003c/em\u003e\u003c/sub\u003e, the map is split along the channel centerline, defining a left half (L) and a right half (R) of equal width. The planform asymmetry is defined as the difference in mean relief change between the right and left halves, normalized by depth (Eq.\u0026nbsp;\u003cspan refid=\"Equ3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Then, compute the mean Δ\u003cem\u003ez\u003c/em\u003e/\u003cem\u003eh\u003c/em\u003e over each half, ⟨\u003cem\u003eΔz\u003c/em\u003e/\u003cem\u003eh\u003c/em\u003e⟩\u003csub\u003eᴸ\u003c/sub\u003e and ⟨\u003cem\u003eΔz\u003c/em\u003e/\u003cem\u003eh\u003c/em\u003e⟩\u003csub\u003eᴿ\u003c/sub\u003e, using all cells (positive and negative). By definition, \u003cem\u003ePAI\u003c/em\u003e\u003csub\u003e\u003cem\u003eh\u003c/em\u003e\u003c/sub\u003e\u0026gt;0 indicates a right-leaning bias (more deposition/scour on the right side), \u003cem\u003ePAI\u003c/em\u003e\u003csub\u003e\u003cem\u003eh\u003c/em\u003e\u003c/sub\u003e\u0026lt;0 indicates a left-leaning bias, and \u003cem\u003ePAI\u003c/em\u003e\u003csub\u003e\u003cem\u003eh\u003c/em\u003e\u003c/sub\u003e= 0 means the changes are laterally balanced.\u003c/p\u003e\u003cp\u003eThe right-bank deposition share, \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e, is a volume-based metric that measures what fraction of the total deposition occurred on the right half of the channel (see Eq.\u0026nbsp;\u003cspan refid=\"Equ4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). This metric complements \u003cem\u003ePAI\u003c/em\u003e\u003csub\u003e\u003cem\u003eh\u003c/em\u003e\u003c/sub\u003e by pinpointing which bank (if any) accumulates more deposited material, thus helping to link observed bar-crest growth or migration to one side of the channel.\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\:{S}_{r}=100\u0026middot;{V}_{⁺ᴿ}/({V}_{⁺ᴸ}+{V}_{⁺ᴿ})$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eTo compute \u003cem\u003eS\u003c/em\u003e\u003csub\u003e\u003cem\u003er\u003c/em\u003e\u003c/sub\u003e, first compute the total volume-equivalent of deposition in each half of the channel (integrating positive \u003cem\u003eΔz\u003c/em\u003e values, normalized by depth). For the left and right halves, sum only the positive Δ\u003cem\u003ez\u003c/em\u003e/\u003cem\u003eh\u003c/em\u003e values: \u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003e⁺ᴸ\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;Σ(max(\u003cem\u003eΔz\u003c/em\u003e,0)/\u003cem\u003eh\u003c/em\u003e) over the left half, \u003cem\u003eV\u003c/em\u003e\u003csub\u003e\u003cem\u003e⁺ᴿ\u003c/em\u003e\u003c/sub\u003e analogously on the right.\u003c/p\u003e\u003cp\u003eThe volumetric dominance metrics, \u003cem\u003eΦ⁺\u003c/em\u003e and \u003cem\u003eΦ⁻\u003c/em\u003e (see Eq.\u0026nbsp;\u003cspan refid=\"Equ5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), characterize the overall sediment budget of the reach in terms of deposition vs. scour. These metrics weight changes by their depth (volume), so they can reveal whether deposition or erosion dominates the reach even when areal coverage (\u003cem\u003eF\u003c/em\u003e\u003csup\u003e₊\u003c/sup\u003e vs \u003cem\u003eF\u003c/em\u003e\u003csup\u003e₋\u003c/sup\u003e) might suggest a different balance.\u003cdiv id=\"Equ5\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ5\" name=\"EquationSource\"\u003e\n$$\\:{{\\Phi\\:}}^{+}=100\u0026middot;{V}^{+}/({V}^{+}+{|V}^{-}|)\\:\\text{a}\\text{n}\\text{d}\\:{{\\Phi\\:}}^{-}=100-\\:{{\\Phi\\:}}^{+}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e5\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe total deposited volume \u003cem\u003eD⁺\u003c/em\u003e = Σ[max(Δ\u003cem\u003ez\u003c/em\u003e, 0)] (sum of all positive bed changes) and total scour volume \u003cem\u003eD⁻\u003c/em\u003e = Σ[min(Δ\u003cem\u003ez\u003c/em\u003e, 0)] (absolute sum of all negative bed changes). To allow comparison between stages, depth-normalized these volumes: \u003cem\u003eV⁺\u003c/em\u003e = \u003cem\u003eD⁺\u003c/em\u003e / \u003cem\u003eh\u003c/em\u003e and \u003cem\u003eV⁻\u003c/em\u003e = | \u003cem\u003eD⁻\u003c/em\u003e| / \u003cem\u003eh\u003c/em\u003e, using the water depth \u003cem\u003eh\u003c/em\u003e. In essence, \u003cem\u003eΦ⁺\u003c/em\u003e represents the percentage of the total sediment volume change that is depositional. Unlike \u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e (which is an area fraction), \u003cem\u003eΦ⁺\u003c/em\u003e incorporates the magnitude of elevation changes, not just their extent, providing a complementary view of whether deposition or scour is volumetrically dominant.\u003c/p\u003e\u003cp\u003eThe normalized morphometric indices capture how the channel bed reorganizes as vegetation is removed. The areal deposition fraction (\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e) measures the proportion of the bed surface experiencing net aggradation and thus indicates whether the system behaves as a depositional or erosional field. Volumetric fractions (\u003cem\u003eΦ⁺\u003c/em\u003e, \u003cem\u003eΦ⁻\u003c/em\u003e) measure the share of total bed-volume change due to aggradation vs. scour (magnitude-weighted), so \u003cem\u003eΦ\u003c/em\u003e complements \u003cem\u003eF\u003c/em\u003e by indicating how deep/substantial the changes are, not just how widespread. The planform asymmetry index (\u003cem\u003ePAIₕ\u003c/em\u003e) quantifies the lateral tilt of deposition, where positive values represent right-bank dominance typical of deflector-type wakes, while values near zero signify symmetry and balance. The right-bank deposition share (\u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e) expresses how much of the total deposited volume accumulates on the right side of the channel, reflecting the extent of lateral bar migration or confinement. Together, these metrics link directly to bar morphology: high \u003cem\u003eF, Φ\u003c/em\u003e, with near-zero \u003cem\u003ePAIₕ\u003c/em\u003e and \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e \u0026asymp; 0.5 imply a broad, laterally even depositional bar, whereas low \u003cem\u003eF\u003c/em\u003e, \u003cem\u003eΦ\u003c/em\u003e\u003csup\u003e\u003cem\u003e+\u003c/em\u003e\u003c/sup\u003e\u0026lt;\u0026lt;\u003cem\u003eΦ\u003c/em\u003e\u003csup\u003e\u003cem\u003e⁻\u003c/em\u003e\u003c/sup\u003e with strongly positive \u003cem\u003ePAIₕ\u003c/em\u003e and \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e \u0026gt;0.5 describe a contracted, right-leaning scour zone driven by flow deflection.\u003c/p\u003e\u003cp\u003eTo expose near-patch hydraulics, we use four patch-aligned locations. L1\u0026mdash;leading edge (stagnation) where an \u0026lsquo;edge trench\u0026rsquo; forms post-cut; L2\u0026mdash;patch center; L3\u0026mdash;lee axis (wake core/reattachment path); L4\u0026mdash;far-bank crest that collects redistributed sediment.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 River Scaling\u003c/h2\u003e\u003cp\u003eTranslating flume morphodynamics to the river scale is challenging because all similarity constraints cannot be satisfied simultaneously [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. The main difficulty comes from the inability to simultaneously satisfy all relevant dimensionless scaling parameters, especially the Froude number and the Shields parameter [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. This leads to experimental setups that often employ steeper slopes compared to nature to sustain sediment transport at limited flow depths [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eRather than pursuing perfect geometric or dynamic similarity, which is impractical, this study prioritizes process-based similarity by carefully selecting hydraulic parameters to replicate sediment motion and alternate bar formation dynamics representative of natural systems. Maintaining the Shields parameter above its critical threshold ensures bedload-dominated transport processes. This approach is widely accepted for investigating complex bio-morphodynamic interactions under controlled laboratory conditions [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e"},{"header":"3. RESULTS","content":"\u003cp\u003eThe morphodynamic response was analyzed under two steady discharges, Case 1: \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e1\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.0025 m\u0026sup3; s⁻\u0026sup1; and Case 2: \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;0.003 m\u0026sup3; s⁻\u0026sup1;, a forced, non-migrating alternate-bar generated by a transverse inlet block. The experimental sequence was consistent for both discharges: NN (non-vegetated baseline), V\u003csub\u003eus\u003c/sub\u003e (vegetated equilibrium), V\u003csub\u003eur1\u003c/sub\u003e (Stage 1: partial removal), and V\u003csub\u003eur2\u003c/sub\u003e (Stage 2: complete removal). Representative bed elevation contour maps for each stage are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e for \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e for \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e. Vegetation patches were semicircular (radius 0.3 m), emergent, and densely staggered (\u003cem\u003eG\u003c/em\u003e/\u003cem\u003eD\u003c/em\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;2.2), positioned on the bar apex facing the flow. The two-stage removal excised 30% of the patch cover in Stage 1 and the remaining 70% in Stage 2, with equilibration periods after each.\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Baseline Morphologies\u003c/h2\u003e\u003cp\u003eA transverse inlet block generated a forced, non-migrating bar train (mode \u003cem\u003em\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1), establishing a repeatable baseline. Consistent with linear theory for forced bars at modest aspect ratio (\u003cem\u003eW\u003c/em\u003e/(2\u003cem\u003eh\u003c/em\u003e)\u0026thinsp;\u0026asymp;\u0026thinsp;14\u0026ndash;17) and subcritical Froude numbers (\u003cem\u003eFr\u003c/em\u003e\u0026thinsp;≲\u0026thinsp;0.9), measured wavelengths at equilibrium were about 10 \u003cem\u003eW\u003c/em\u003e (\u003cem\u003eQ₁\u003c/em\u003e) and 11 \u003cem\u003eW\u003c/em\u003e (\u003cem\u003eQ₂\u003c/em\u003e), in line with Phase-I characterization and analytic scaling for hybrid bars [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. For moderate width‑to‑depth (\u003cem\u003eW\u003c/em\u003e/\u003cem\u003eh\u003c/em\u003e) and subcritical Froude numbers, the steady-bar framework predicts a most-likely bar mode controlled primarily by \u003cem\u003eW\u003c/em\u003e/\u003cem\u003eh\u003c/em\u003e, with steady patterns expected under planform or obstacle forcing [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. Longitudinal elevation profiles (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a) and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a)) show the canonical alternation of shoal and pool, with downstream propagation arrested by the upstream forcing; the bars lengthened and stabilized in place as equilibrium was approached, precisely as described for hybrid trains with localized perturbations. Under equilibrium conditions (V\u003csub\u003eus\u003c/sub\u003e), the patch produced a front-edge stagnation trench and a lee deposition corridor, yielding a right-leaning planform. These signatures were present at both discharges and emerged earlier and more strongly at \u003cem\u003eQ₂\u003c/em\u003e than at \u003cem\u003eQ₁\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b) and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b).\u003c/p\u003e\u003cp\u003eA finite emergent patch increases drag and intensify lateral flow at the vegetation\u0026ndash;clear‑flow interface (Location L1); turbulence production and wake sheltering trap sediment within/behind the patch while diverting the core jet toward the opposite bank [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b) and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b) display the same phenomena: deposition in and just behind every patch and scour on the opposite bank, with the effect stronger at \u003cem\u003eQ₂\u003c/em\u003e (greater mobility). In this forced‑bar setting, these manifest as a mild lengthening of local crest\u0026ndash;trough spacing (storage) without changing the global mode (\u003cem\u003em\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1). An experimental study reports that vegetation lengthens wavelength and stabilizes the planform, with stronger expression at higher discharge [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.2 State Shift: Areal and Lateral Reorganization After Vegetation Removal\u003c/h2\u003e\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\u003ch2\u003e3.2.1 Stage‑1 (V\u003csub\u003eur1\u003c/sub\u003e): partial, leading‑edge cut\u003c/h2\u003e\u003cp\u003eFollowing the Stage 1 removal of the leading\u0026thinsp;~\u0026thinsp;30% of the patch, the morphology changed significantly. The zone of maximum scour shifted from the original patch front to the newly exposed leading edge, and depositional patterns in the lee of the patch were reorganized (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c), Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(c)). Relative to the vegetated baseline (V\u003csub\u003eus\u003c/sub\u003e), the Stage-1 truncation immediately reorganizes patch-scale hydraulics by weakening the front-face stagnation and breaking the continuous sheltering within the footprint. \u0026ldquo;In \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e, this is evident by comparing Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b) (Case1-V\u003csub\u003eus\u003c/sub\u003e) with the Stage-1 maps in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c\u0026ndash;d) (Case1-V\u003csub\u003eur1\u003c/sub\u003e): the impingement zone at L1\u003csub\u003ei\u003c/sub\u003e and L1\u003csub\u003ej\u003c/sub\u003e retreats along the semicircle arc and its peak orange\u0026ndash;red signal (scour) diminishes, while scour tongues intrude the canopy interior at L2\u003csub\u003ei\u003c/sub\u003e and L2\u003csub\u003ej\u003c/sub\u003e as through-patch leakage replaces the former deflection pattern. Downstream, the lee-axis minimum (L3\u003csub\u003ei/j\u003c/sub\u003e) elongates and advects, with a slight rotation consistent with the alternate-bar front.\u003c/p\u003e\u003cp\u003eThe exact mechanism strengthens under \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e: relative to Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b) (Case2-V\u003csub\u003eus\u003c/sub\u003e), Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e (c\u0026ndash;d) (Case2-V\u003csub\u003eur1\u003c/sub\u003e) shows a decisive L1 collapse, a coherent interior-scour core at L2, and a farther-advected L3, consistent with a longer reattachment length at higher discharge. Partial vegetation removal abruptly shifts the bar from scour-dominated to deposition-dominated, re-centering sediment laterally and reducing planform asymmetry, particularly at \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\u003cp\u003eChannel-scale consequence: a discharge-dependent state shift and re-phasing of the alternate bar initiated by Stage-1. Mechanistically, Stage-1 reproduces natural, scour-assisted uprooting: edge scour undermines rooting, shortens the first reattachment, and flips the bar from a deflector-type wake to a diffuser-type wake. The partial removal of the leading edge breaches this frontal barrier. Rather than deflecting, flow penetrates the patch, where stems dissipate momentum and spread it outward like a hydraulic diffuser. This eliminates the large, sheltered wake, increases turbulence and scour within the patch interior (L2), and creates a more disorganized, advected wake downstream. This hydraulic shift from deflection to diffusion is evident in the morphological response.\u003c/p\u003e\u003cp\u003eUnder \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e, the V\u003csub\u003eus\u003c/sub\u003e deflector weakens to a momentum diffuser: L1\u003csub\u003ei/j\u003c/sub\u003e loses its stagnation anchor, L2\u003csub\u003ei/j\u003c/sub\u003e shifts towards scour, and L3\u003csub\u003ei/j\u003c/sub\u003e translates modestly. Meanwhile, L4\u003csub\u003ei/j\u003c/sub\u003e shows moderate accretion without complete bar reorganization (compare Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c\u0026ndash;d) to Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b)). Under \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e, the same sequence is amplified: L1\u003csub\u003ei/j\u003c/sub\u003e diffuses, L2\u003csub\u003ei/j\u003c/sub\u003e scours more strongly, L3\u003csub\u003ei/j\u003c/sub\u003e lengthens and shifts farther downstream, and L4\u003csub\u003ei/j\u003c/sub\u003e advances more clearly as the far-bank lobe gains dominance (compare Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e (c\u0026ndash;d) to Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b)).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\u003ch2\u003e3.2.2 Stage‑2 (V\u003csub\u003eur2\u003c/sub\u003e): Complete removal\u003c/h2\u003e\u003cp\u003eUnder \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e,\u003c/sub\u003e the complete vegetation removal reinforces Stage-1 trends, establishing a new patch-scale morphology (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(e\u0026ndash;f), Case 1-V\u003csub\u003eur2\u003c/sub\u003e). The stagnation zone disperses: L1\u003csub\u003ek\u003c/sub\u003e shows diffuse, weak scour, and L1\u003csub\u003el\u003c/sub\u003e lacks the arc-focused hotspot, confirming the loss of stable impingement. Inside the footprint, a coherent interior-scour core develops at L2\u003csub\u003ek\u003c/sub\u003e and persists at L2\u003csub\u003el\u003c/sub\u003e, consistent with sustained scour once the shelter is removed. Lee response intensifies: L3\u003csub\u003ek\u003c/sub\u003e\u0026rsquo;s wake minimum elongates and shifts further downstream while the far bank bar becomes the dominant depositional feature. L4\u003csub\u003ek\u003c/sub\u003e already shows green\u0026ndash;blue lobe growth, and by L4\u003csub\u003el\u003c/sub\u003e, the crest is advanced and widened, consistent with a more extended separation length and downstream reattachment.\u003c/p\u003e\u003cp\u003eUnder \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e, this progression is more pronounced (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e (e\u0026ndash;f), Case2-V\u003csub\u003eur2\u003c/sub\u003e). L1\u003csub\u003ek\u003c/sub\u003e\u0026rsquo;s front-face control collapses rapidly and disappears by L1\u003csub\u003el\u003c/sub\u003e. Interior scour at L2\u003csub\u003ek/l\u003c/sub\u003e is stronger and more spatially continuous than in \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e. At the same time, the lee minimum L3\u003csub\u003ek\u003c/sub\u003e extends farther and remains advected at L3\u003csub\u003el\u003c/sub\u003e, indicating a longer reattachment distance and intensified cross-stream momentum exchange. The opposite-bank bar L4 responds vigorously, with a clear crest advance and lobe thickening; the depositional footprint occupies a larger fraction of the reach than in \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e, signaling a decisive re-phasing of the alternate-bar pattern at the higher discharge.\u003c/p\u003e\u003cp\u003eRelative to the partial leading-edge cut (V\u003csub\u003eur1\u003c/sub\u003e; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e (c\u0026ndash;d) \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e; Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e (c\u0026ndash;d) \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e), complete removal (V\u003csub\u003eur2\u003c/sub\u003e) eliminates residual deflection and yields a persistent diffuser: L1 transitions from a weakened stagnation zone to a diffuse, non-anchoring front; L2 from mixed response to persistent interior scour; L3 lengthens/advects; L4 progresses from incipient to dominant crest advance.\u003c/p\u003e\u003cp\u003ePlan-view elevation maps for complete removal (V\u003csub\u003eur2\u003c/sub\u003e) are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e (a\u0026ndash;b). Relative to V\u003csub\u003eur1\u003c/sub\u003e, the front-edge trench broadens and shallows, the lee minimum translates farther downstream, and deposition consolidates along the opposite-bank crest. At higher discharges, the depositional footprint occupies a larger fraction of the reach, and the wake reattachment lengthens, consistent with the longer-wavelength bar train that we quantify later. These maps capture the planform expression of the completed re-phasing described in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Edge-trench onset and wake reorganization across the vegetation (from V\u003csub\u003eus\u003c/sub\u003e to V\u003csub\u003eur2\u003c/sub\u003e)\u003c/h2\u003e\u003cp\u003eAt \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e, V\u003csub\u003eus\u003c/sub\u003e exhibits a front-edge trench (Δ\u003cem\u003ez\u003c/em\u003e/\u003cem\u003eh\u003c/em\u003e \u0026asymp; \u0026minus;\u0026thinsp;1.2; Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a)) and mild lee deposition. Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the normalized bed-relief across each discharge. V\u003csub\u003eur1\u003c/sub\u003e disrupts the trench\u0026ndash;wake balance: infill begins, and downstream deposition intensifies (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(b)). Relief increases by Δ\u003cem\u003ez\u003c/em\u003e/\u003cem\u003eh\u003c/em\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;+\u0026thinsp;1.0 (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), indicating sediment reallocation from trench to lee. V\u003csub\u003eur2\u003c/sub\u003e consolidates this arrangement, maintaining high deposition and smoothing the relief (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(c)). Overall, at \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e, the main morphodynamic work occurs during Stage 1, while Stage 2 primarily stabilizes the newly organized depositional corridor.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eSummary of normalized bed-relief (\u003cem\u003eΔz/h\u003c/em\u003e) and morphodynamics metrics for \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e and \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e across stages (V\u003csub\u003eus\u003c/sub\u003e, V\u003csub\u003eur1\u003c/sub\u003e, V\u003csub\u003eur2\u003c/sub\u003e)\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"8\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDischarge\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eLocation\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eStage\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eMean \u003cem\u003eΔz/h\u003c/em\u003e trend\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eAreal trend \u003c/p\u003e\u003cp\u003e(\u003cem\u003eF\u003c/em\u003e\u003csup\u003e₊\u003c/sup\u003e, \u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₋\u003c/em\u003e\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eLateral trend (\u003cem\u003ePAIₕ\u003c/em\u003e, \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eVolumetric Trend (\u003cem\u003eΦ⁺\u003c/em\u003e / \u003cem\u003eΦ⁻\u003c/em\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eDominant process /\u003c/p\u003e\u003cp\u003eRemarks\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003e\u003cb\u003eQ\u003c/b\u003e\u003csub\u003e\u003cb\u003e1\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eL1 (Front)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eV\u003csub\u003eus\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u0026minus;1.2 (trench)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e \u0026asymp; 25% ≪ \u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₋\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cem\u003ePAIₕ +\u003c/em\u003e0.23, \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e \u0026gt;55%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cem\u003eΦ⁺\u003c/em\u003e \u0026asymp; 35% /\u003c/p\u003e\u003cp\u003e\u003cem\u003eΦ⁻\u003c/em\u003e \u0026asymp; 6 %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eEdge scour- Vegetation deflects flow, creating a deep trench at the front.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eV\u003csub\u003eur1\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e+\u0026thinsp;0.3 (infilling)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e \u0026asymp; 70% ≫ \u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₋\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cem\u003ePAIₕ\u003c/em\u003e \u0026asymp; 0, \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e \u0026asymp; 50%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cem\u003eΦ⁺\u003c/em\u003e \u0026asymp; 72% / \u003c/p\u003e\u003cp\u003e\u003cem\u003eΦ⁻\u003c/em\u003e \u0026asymp; 2 %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eTrench reduction\u0026thinsp;+\u0026thinsp;lee growth, Threshold flip: scour\u0026rarr;deposition\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eV\u003csub\u003eur2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e+\u0026thinsp;0.1 (stable)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e \u0026asymp; 73%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cem\u003ePAIₕ\u003c/em\u003e \u0026asymp; 0, \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e \u0026asymp; 50%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cem\u003eΦ⁺\u003c/em\u003e \u0026asymp; 74% / \u003c/p\u003e\u003cp\u003e\u003cem\u003eΦ⁻\u003c/em\u003e \u0026asymp; 2 %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eWake stabilizes - Balanced deposition maintained\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eL2 (Interior)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eAll\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e+\u0026thinsp;0.8\u0026ndash;1.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e \u0026gt;\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₋\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cem\u003ePAIₕ\u003c/em\u003e \u0026asymp; 0, \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e \u0026asymp; 50%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cem\u003eΦ⁺\u003c/em\u003e \u0026asymp; 70\u0026ndash;75% / \u003cem\u003eΦ⁻\u003c/em\u003e \u0026asymp; 25\u0026ndash;30%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eCore aggradation, lee corridor broadens and levels.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eL3 (Lee)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eAll\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u0026minus;0.1 \u0026rarr; +1.0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e \u0026uarr;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eSlight left-shift\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cem\u003eΦ⁺\u003c/em\u003e \u0026asymp; 75% / \u003c/p\u003e\u003cp\u003e\u003cem\u003eΦ⁻\u003c/em\u003e \u0026asymp; 2 %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eCoherent lee-wedge formation, organized wake deposition.\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e\u003cp\u003e\u003cb\u003eQ\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eL1 (Front)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eV\u003csub\u003eus\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e+\u0026thinsp;0.3 (weak trench)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e \u0026asymp; 20% ≪ \u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₋\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cem\u003ePAIₕ\u003c/em\u003e +0.15, \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e \u0026gt;60%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cem\u003eΦ⁺\u003c/em\u003e \u0026asymp; 30% / \u003c/p\u003e\u003cp\u003e\u003cem\u003eΦ⁻\u003c/em\u003e \u0026asymp; 7 %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eWeak scour-edge still armored\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eV\u003csub\u003eur1\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e+\u0026thinsp;1.2 (peak uplift)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e \u0026asymp; 56%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cem\u003ePAIₕ\u003c/em\u003e \u0026asymp; 0. \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e \u0026asymp; 50%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cem\u003eΦ⁺\u003c/em\u003e \u0026asymp; 68% / \u003c/p\u003e\u003cp\u003e\u003cem\u003eΦ⁻\u003c/em\u003e \u0026asymp; 3 %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eTrench uplift and flow contraction - Stronger flip than Q₁\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eV\u003csub\u003eur2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e+\u0026thinsp;0.9 (stable)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e \u0026asymp; 70%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cem\u003ePAIₕ\u003c/em\u003e \u0026asymp; 0. \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e \u0026asymp; 50%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cem\u003eΦ⁺\u003c/em\u003e \u0026asymp; 72% / \u003c/p\u003e\u003cp\u003e\u003cem\u003eΦ⁻\u003c/em\u003e \u0026asymp; 2 %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eDiffused trench - Sustained depositional dominance\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eL2 (Interior)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eAll\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u0026minus;0.6 \u0026rarr; 0.0 \u0026rarr; +0.7\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;\u003cem\u003eΦ\u003c/em\u003e\u003csup\u003e\u003cem\u003e⁺\u003c/em\u003e\u003c/sup\u003e \u0026uarr;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eBalanced\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cem\u003eΦ⁺\u003c/em\u003e \u0026asymp; 70\u0026ndash;75% / \u003cem\u003eΦ⁻\u003c/em\u003e \u0026asymp; 25\u0026ndash;30%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eInterior flattening - Loss of the core scour zone\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eL3 (Lee)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003eAll\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u0026minus;0.7 \u0026rarr; +1.1 \u0026rarr; +0.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e \u0026uarr;\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003eSlight right-lean\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cem\u003eΦ⁺\u003c/em\u003e \u0026asymp; 75% / \u003c/p\u003e\u003cp\u003e\u003cem\u003eΦ⁻\u003c/em\u003e \u0026asymp; 2 %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003eLee fill\u0026thinsp;+\u0026thinsp;downstream translation - longer reattachment, stronger wake\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eNote\u003c/strong\u003e: Patch Location, L1-Front, L2-Interior, L3-Lee, morphometric indices\u0026mdash;\u003cem\u003eF\u003c/em\u003e (areal fraction), \u003cem\u003ePAIₕ\u003c/em\u003e (lateral asymmetry), \u003cem\u003e\u0026Phi;\u003c/em\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e(volumetric dominance),\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eand \u003cem\u003eSᵣ\u003c/em\u003e (right-bank share of deposition).\u003c/p\u003e\u003cp\u003eAt \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e, the sequence repeats with stronger dynamics. Under V\u003csub\u003eus\u003c/sub\u003e, the trench is shallower (Δ\u003cem\u003ez\u003c/em\u003e/\u003cem\u003eh\u003c/em\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;+\u0026thinsp;0.3; Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(d)), and sediment starts bypassing the patch edges. Stage 1 (V\u003csub\u003eur1\u003c/sub\u003e) triggers a pronounced scour slot at L1 while simultaneously building a strong depositional wedge at L3 (Δ\u003cem\u003ez\u003c/em\u003e/\u003cem\u003eh\u003c/em\u003e\u0026thinsp;\u0026asymp;\u0026thinsp;+\u0026thinsp;1.1; Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(e)). Flow reattachment occurs closer to the patch, shortening the wake and concentrating deposition. V\u003csub\u003eur2\u003c/sub\u003e (Stage 2) further widens the trench and shifts deposition downstream, smoothing the profile toward a free-bar state (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(f)). This promotes greater bar mobility at \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e, with longer scour\u0026ndash;fill oscillations and more dynamic re-spacing than at \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003e3.4 Normalized morphometrics and areal bias\u003c/h2\u003e\u003cp\u003eNormalized indices/metrics (\u003cem\u003eF\u003c/em\u003e, \u003cem\u003eΦ, PAIₕ\u003c/em\u003e, \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e) show a systematic shift from scour-dominant, right-leaning (V\u003csub\u003eus\u003c/sub\u003e) to deposition-dominant, more symmetric states with staged removal across each discharge (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e; Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eUnder the vegetated equilibrium (V\u003csub\u003eus\u003c/sub\u003e), both discharges show a clear scour-dominated configuration, with \u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e \u0026asymp; 20\u0026ndash;25% and \u003cem\u003eΦ⁺\u003c/em\u003e \u0026lt; 35% (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a-b)). The bar\u0026rsquo;s relief is asymmetric, marked by strong right-bank bias (\u003cem\u003ePAIₕ\u003c/em\u003e \u0026gt;0, \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e \u0026asymp; 60%) (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(c-d)), confirming a flow-deflecting canopy that concentrates shear at the patch front and diverts the core jet laterally. This vegetated morphology thus represents a stable, deflector-type reference state dominated by frontal trenching and localized deposition behind the patch.\u003c/p\u003e\u003cp\u003eV\u003csub\u003eur1\u003c/sub\u003e introduces a central morphological pivot. The leading-edge removal weakens the deflector effect, redistributing flow more evenly across the section. Areal deposition expands rapidly (\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e \u0026asymp; 55\u0026ndash;77%) (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a). While volumetric accumulation nearly doubles as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b) (\u003cem\u003eΦ⁺\u003c/em\u003e \u0026asymp; 65\u0026ndash;75%), indicating a shift from scour-dominated to deposition-dominant behavior. Lateral indices flatten (\u003cem\u003ePAIₕ\u003c/em\u003e \u0026asymp;0, \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e \u0026asymp; 50%), signaling balanced sediment storage on both banks (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(c\u0026ndash;d)). Morphodynamically, Stage 1 transforms a confined, vegetation-forced bar into a diffuse depositional corridor. The former trench zone begins to fill, and the downstream wake strengthens\u0026mdash;an inflection clearly visible in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e and confirmed across all cross-sections in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e\u003cp\u003eV\u003csub\u003eur2\u003c/sub\u003e completes and stabilizes this transition. The frontal scour diffuses, and broad deposition dominates the planform (\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e \u0026asymp; 53\u0026ndash;73%, \u003cem\u003eΦ⁺\u003c/em\u003e \u0026asymp; 70\u0026ndash;80%). Slightly negative \u003cem\u003ePAIₕ\u003c/em\u003e values indicate a mild left-lean under some realizations, yet overall, the configuration approaches a laterally balanced free-bar equilibrium. Stage 2, therefore, consolidates the Stage-1 change, yielding a smoother, lower-relief surface where energy distribution and sediment transport become more symmetric (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a\u0026ndash;d).\u003c/p\u003e\u003cp\u003eThe patch-scale observations (P1\u0026ndash;P3) reveal that the strength of this adjustment depends on position within the bar (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(a\u0026ndash;b)). At \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e, the apex patch (P2) exhibits the strongest Stage 1 flip\u0026mdash;from right-biased scour (\u003cem\u003ePAIₕ\u003c/em\u003e \u0026asymp; +0.48) to left-leaning deposition (\u003cem\u003ePAIₕ\u003c/em\u003e \u0026asymp; \u0026minus;0.1)\u0026mdash;while flank patches (P1, P3) show milder shifts due to partial hydraulic shielding. At higher discharge (\u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e), newly mobilized sediment is partly exported downstream, causing local \u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e to decline slightly. At the same time, Φ⁺ remains high (\u0026gt;\u0026thinsp;70%), indicating that volumetrically the reach continues to aggrade even if local surfaces fluctuate. Overall, the morphometric indices reveal a non-linear progression of channel adjustment: vegetation imposes asymmetry and scour concentration, partial uprooting reverses it abruptly, and complete removal stabilizes the new, deposition-dominant morphology.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003e3.5 Longitudinal Adjustment: Bar Wavelength and Phasing\u003c/h2\u003e\u003cp\u003eUprooting influences the longitudinal organization of alternate bars by altering both the wavelength (\u003cem\u003eλ\u003c/em\u003e) and the crest\u0026ndash;trough phasing (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). In the vegetated cases (V\u003csub\u003eus\u003c/sub\u003e), the bar exhibits pronounced relief and slightly elongated spacing compared to the non-vegetated reference (NN). Their crests/troughs are clearly out of phase with Phase 1 (alternate bars) over several reaches (e.g., between ~\u0026thinsp;0.5\u0026ndash;1 m), indicating a vegetation-induced shift of the bar couplet (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(a)). Peak picking on the detrended thalweg shows that the mean wavelength of the vegetated sequence is \u0026asymp;\u0026thinsp;5.6 m, whereas Phase 1 (alternate bars) retains a longer spacing of \u0026asymp;\u0026thinsp;5 m. When discharge increases to \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e, the vegetated wavelength remains near \u0026asymp;\u0026thinsp;7 m, while the Phase 1 (alternate bars) wavelength compresses to \u0026asymp;\u0026thinsp;6 m; as a result, V\u003csub\u003eus\u003c/sub\u003e becomes\u0026thinsp;~\u0026thinsp;10% longer than Phase 1 (alternate bars) (see Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(b). V\u003csub\u003eur1\u003c/sub\u003e initiates a measurable longitudinal adjustment, the magnitude of which depends on discharge. At \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003eλ\u003c/em\u003e contracts modestly\u0026mdash;about 4% shorter than NN\u0026mdash;signaling the collapse of the vegetative deflector and local infilling behind the former trench. At \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e, however, V\u003csub\u003eur1\u003c/sub\u003e produces the opposite effect: wavelength lengthens by +\u0026thinsp;10\u0026ndash;33%, indicating that increased discharge transforms the wake from confined to diffusive.\u003c/p\u003e\u003cp\u003eV\u003csub\u003eur2\u003c/sub\u003e reinforces and stabilizes the Stage-1 trajectory. At \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e, \u003cem\u003eλ\u003c/em\u003e recovers slightly (+\u0026thinsp;4% above NN), approaching the natural spacing of free bars, while at \u003cem\u003eQ₂\u003c/em\u003e it increases markedly (+\u0026thinsp;43\u0026ndash;59%), yielding fewer and more persistent bar cells. The longitudinal thalweg profiles (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(b) clearly show the expansion of low-frequency oscillations and downstream translation of crests, indicating longer morphodynamics cells and slower bar migration. Across \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u0026ndash;\u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e, V\u003csub\u003eur1\u003c/sub\u003e initiates the state shift (trench decay, corridor formation, modest \u003cem\u003eλ\u003c/em\u003e regularization); V\u003csub\u003eur2\u003c/sub\u003e stabilizes it (persistent corridor, symmetric morphometrics, regular wavelength).\u003c/p\u003e\u003cp\u003eThe wavelength data reveal a scale-dependent re-phasing of bar morphology. Vegetation lengthens and stabilizes the bar pattern, partial removal relaxes this constraint and reorganizes bar rhythm, and complete clearing restores intrinsic flow-controlled spacing. The interplay of discharge and vegetation control defines a non-linear continuum of morphodynamic states, with Stage 1 as the tipping point and Stage 2 as the equilibrium consolidation phase.\u003c/p\u003e\u003cp\u003eTogether, the two discharges define a coherent trend: uprooting induces a morphodynamic re-phasing where wavelength responds non-linearly to vegetation removal. Stage 1 initiates the bar-length growth; Stage 2 consolidates it, particularly under high discharge. Morphodynamically, this demonstrates that vegetation loss not only reorganizes local scour and deposition but also scales up to alter the fundamental bar spacing and propagation rhythm (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e"},{"header":"4. DISCUSSION","content":"\u003cp\u003eThe sequential removal protocol was not just an experimental convenience; it was designed as an intentional process: the leading-edge cut mimics the scour-mediated (Type II) uprooting failure of established plants, where local trenching by horseshoe vortices undermines root anchorage, thereby clarifying why the V\u003csub\u003eur1\u003c/sub\u003e \u0026lsquo;flip\u0026rsquo; is abrupt rather than gradual [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. This makes the Stage-1 flip directly comparable to natural flood-induced vegetation loss at bar fronts. The initial cylinder embedment depth was set to 0.1 m to ensure firm anchorage, yet it remained shallow enough that scour below this depth would induce uprooting [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. During the vegetated equilibrium, localized scour at the patch's hydraulically vulnerable leading edge reduced the local sediment thickness [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. This scour-induced reduction in anchoring depth represents the threshold at which the frontal vegetation becomes vulnerable to uprooting. Therefore, the manual sequential vegetation removal in Phase III is a controlled simulation of this uprooting, allowing for the systematic quantification of the sandbar's morphological response to a known magnitude of disturbance.\u003c/p\u003e\u003cp\u003eThis study reveals that the progressive removal of vegetation triggers a pronounced, non-linear state shift. Partial, leading-edge removal acts as a threshold disturbance that flips an alternate bar from scour-dominant (~\u0026thinsp;20\u0026ndash;25% aggrading area) to deposition-dominant (~\u0026thinsp;56\u0026ndash;77%), indicating a discrete state change rather than linear interpolation between end-members. This Stage-1 response matches the signature of scour-mediated (Type-II) uprooting, where leading-edge trenching undermines anchorage and reorganizes the wake. The following sections synthesize the mechanism, practical implications, and limits on transferability.\u003c/p\u003e\u003cp\u003eThis marks a threshold behavior\u0026mdash;under low flow, partial removal shortens the bar train through localized sediment trapping; under high flow, it releases sediment farther downstream, creating broader, more widely spaced bars. V\u003csub\u003eur1\u003c/sub\u003e thus serves as the principal phase of bar re-organization, corresponding to the morphodynamic \u0026ldquo;pivot\u0026rdquo; from a deflector-type wake to a diffuser-type one. Vegetation behaves as a finite deflector that concentrates shear at the patch front and shelters its lee, producing deeper troughs, taller deposits, and longer bar wavelengths than bare beds [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. The vegetated baseline (low \u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e and \u003cem\u003eΦ⁺\u003c/em\u003e, high \u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₋\u003c/em\u003e\u003c/sup\u003e and \u003cem\u003eΦ\u003c/em\u003e\u003csup\u003e\u003cem\u003e\u0026minus;\u003c/em\u003e\u003c/sup\u003e; \u003cem\u003ePAIₕ\u003c/em\u003e\u0026gt;0; \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e\u0026gt;50%) is therefore consistent with classic patch-wake hydraulics for wall-attached and mid-channel patches [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e].\u003c/p\u003e\u003cp\u003ePartial removal short-circuits deflector control, shortening reattachment and relaxing spacing toward the free-bar template; field observations similarly report more regular alternate bars formation after removal of roughness elements that had forced irregular patterns [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThe Stage 1 removal transformed the patch from a solid flow deflector to a porous diffuser. This hydraulic shift concentrated shear stress at the new leading edge, carving a distinct scour trench (L1). Simultaneously, it allowed flow into the patch interior, eliminating shelter (L2) and promoting organized deposition in its immediate lee (L3) (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Longitudinally, the crest\u0026ndash;trough couplet contracts immediately downstream (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e), consistent with a shorter reattachment and a depositional lobe shifted toward the far-bank crest. These signatures are expected when wake geometry is controlled by patch size and edge shear, and when partial leading-edge removal or stem flexibility reduces the reattachment length [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]. Mechanistically, the sequence mirrors Type-II uprooting: localized edge scour reduces anchorage and lowers the removal threshold into the range of common floods [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eStage-2 removes the deflector entirely and consolidates the Stage-1 trajectory: the L1 trench diffuses, the lee minimum advects downstream, spacing re-lengthens, and lateral shares remain near balanced (Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e). This relaxation toward a free-bar template aligns with reports that vegetation stabilizes and elongates bars, whereas removal returns systems toward shorter, more mobile bars [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e].\u003c/p\u003e\u003cp\u003ePatch position matters. Windows closer to the bar crest (P2\u0026ndash;P3) show the clearest Stage-1 flip (\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e rises; \u003cem\u003ePAIₕ\u003c/em\u003e trends negative) and Stage-2 stabilization near lateral balance, whereas a marginal window (P1) shows weaker swings (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(a\u0026ndash;b)), consistent with stronger bar\u0026ndash;patch feedback near crests and greater local wavelength control [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. At higher flow, more of the new deposition is exported downstream (local \u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e can remain small while the reach budget \u003cem\u003eΦ⁺\u003c/em\u003e rises), matching the theory that higher discharge promotes more mobile bars with longer reattachment and shorter intrinsic wavelength [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. Across P1\u0026ndash;P3 and both discharges, metrics cohere: \u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e increases, \u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₋\u003c/em\u003e\u003c/sup\u003e declines, \u003cem\u003ePAIₕ\u003c/em\u003e and \u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e move toward balance; spacing contracts near the apex in Stage-1 and re-lengthens in Stage-2, with a stronger, more persistent response at \u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThese patterns align with broader eco-morphodynamic feedback: vegetation reduces near-bed stress and traps sediment, stabilizing and elongating bars, whereas frequent uprooting limits colonization and maintains shorter, more mobile bars [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. Convergent evidence from planform metrics, cross-sections, and longitudinal profiles (Figs.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e), along with independent studies, supports the uprooting-driven re-phasing of alternate bars [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e].\u003c/p\u003e\u003cp\u003ePartial leading-edge clearing concentrates edge shear and shortens the first reattachment, creating a trench hotspot over roughly one to two patch lengths and shifting deposition toward the opposite bank\u0026mdash;consistent with patch-wake mechanics observed in flumes and field canopies [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. Accordingly, selective thinning at bar apices for navigation or conveyance can inadvertently destabilize the remaining bar by intensifying local scour and by redistributing deposition laterally. In contrast, complete clearing tends to stabilize spacing and export a larger share of deposition downstream, moving the reach toward a free-bar template\u0026mdash;aligning with evidence that vegetation elongates/stabilizes bars and that removal relaxes spacing toward intrinsic morphodynamic modes [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. Discharge sensitivity should guide timing and monitoring. Higher flows amplify wake length and deposition footprints, increasing the chance that partial clearing will trigger a threshold flip. Therefore, interventions near the rising limb are more likely to produce strong edge trenching and rapid re-phasing. For post-works surveillance, simple planform indices (aggrading-area share \u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e and right-bank deposition share S\u003csub\u003er\u003c/sub\u003e) provide low-cost early warning of unintended polarity flips or lateral imbalance (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e). Field reports indicate that removing roughness elements can yield more regular alternate bars [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eRigid, emergent cylinders omit reconfiguration and motion-induced drag reduction; flexible or submerged canopies would likely smooth the Stage-1 transition, although the edge-shear/wake mechanism remains the same [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. Steady discharge omits rising/falling-limb hysteresis; rising limbs could advance edge trenching, falling limbs could partially backfill, modulating (not negating) the flip predicted by Type-II mechanics [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Clear-water scour emphasizes local trenching and lee organization; sediment-laden floods would shallow trenches and shift more deposition downstream. Fixed banks suppress bank\u0026ndash;bar coupling and channel widening; in mobile-bank rivers, lateral adjustment would likely strengthen bar shortening and re-phasing. Normalizing relief by Δ\u003cem\u003ez\u003c/em\u003e/\u003cem\u003eh\u003c/em\u003e supports stage-wise comparison but coarsens near-bank contrasts; the inlet perturbation gently favors \u003cem\u003em\u003c/em\u003e\u0026thinsp;=\u0026thinsp;1, biasing reach-scale spacing. Within these bounds, the staged-removal protocol provides a process template for apex patches on alternate bars.\u003c/p\u003e"},{"header":"5. CONCLUSION","content":"\u003cp\u003eThis study demonstrates that the progressive uprooting of vegetation from alternate sandbars induces a threshold-type, non-linear morphodynamic transition. The response to partial removal is not a simple interpolation between the fully vegetated and bare end-member states but rather a distinct dynamic regime. The key findings are summarized below.\u003c/p\u003e\u003cp\u003e\u003cul\u003e\u003cli\u003e\u003cp\u003ePartial uprooting causes a rapid polarity flip from scour-dominated to deposition-dominated morphology, revealing that even minor vegetation loss can cross a stability threshold in bar dynamics. Complete uprooting does not reverse this shift but instead stabilizes and consolidates it.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eThe morphodynamic transition is expressed through increased depositional area (\u003cem\u003eF\u003c/em\u003e\u003csup\u003e\u003cem\u003e₊\u003c/em\u003e\u003c/sup\u003e), reduced lateral asymmetry (\u003cem\u003ePAIₕ\u003c/em\u003e), balanced right-bank deposition (\u003cem\u003eS\u003csub\u003er\u003c/sub\u003e\u003c/em\u003e), and higher volumetric dominance (\u003cem\u003eΦ⁺\u003c/em\u003e). Together, these metrics indicate a fundamental re-phasing of the bar from a forced, asymmetric state to a free-bar configuration.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eVegetation removal alters the bar-scale geometry\u0026mdash;under low discharge (\u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e), wavelength changes are minor (\u0026plusmn;\u0026thinsp;4%), but at high discharge (\u003cem\u003eQ\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e), bars elongate by 10\u0026ndash;60%, reflecting longer wakes and slower bar migration. This scaling confirms that uprooting modifies both the intensity and spatial scale of morphodynamic organization.\u003c/p\u003e\u003c/li\u003e\u003cli\u003e\u003cp\u003eAt higher discharges, the reattachment zone lengthens, bar wavelength expands, and the depositional lobe shifts downstream, amplifying the morphodynamic response. The staged removal mimics natural scour-mediated (Type-II) uprooting, providing an experimental framework to interpret flood-induced vegetation loss and its geomorphic impacts.\u003c/p\u003e\u003c/li\u003e\u003c/ul\u003e\u003c/p\u003e\u003cp\u003eFrom a practical standpoint, the results offer guidance for river management. Selective (partial) vegetation removal \u0026ndash; such as trimming or thinning vegetation patches at the bar during moderate flows \u0026ndash; is expected to intensify local scour for roughly 1\u0026ndash;2 bar lengths downstream. This approach could be used to maintain navigation channels or prevent aggradation in critical sections. Conversely, complete vegetation removal tends to reset the bar morphology to a shorter-wavelength, free-bar state, which stabilizes bar positions but shifts the bars downstream of their original locations. This distinction provides a process-based framework for selecting vegetation management strategies to achieve a specific geomorphic goal. Future work should test flexible/submerged canopies and varied patch densities under unsteady hydrographs, mixed sediments, and mobile banks, capturing both Type-I (drag) and Type-II (scour-mediated) uprooting.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements / Funding:\u0026nbsp;\u003c/strong\u003eThis study was partially funded by a JSPS Grant-in-Aid for Scientific Research (KAKENHI) (No. 24K07677).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions:\u0026nbsp;\u003c/strong\u003eConceptualization: [Saqib Habib, Norio Tanaka], Methodology: [Saqib Habib], Formal analysis and investigation: [Saqib Habib], Visualization: [Saqib Habib], Writing - original draft preparation: [Saqib Habib], Writing - review and editing: [Saqib Habib, Norio Tanaka], Supervision: [Saqib Habib, Norio Tanaka].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability:\u003c/strong\u003e The data that supports the findings of this study are available on the request from the corresponding author.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of Interest:\u0026nbsp;\u003c/strong\u003eThe authors declare that they have no conflicts of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthical approval:\u0026nbsp;\u003c/strong\u003eThis article does not contain any studies with human participants or animals performed by any of the authors.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInformed consent:\u0026nbsp;\u003c/strong\u003eInformed consent was obtained from all individual participants included in the study.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eChurch M, Ferguson R. Morphodynamics: Rivers beyond steady state. Water Resour Res 2015;51:1883\u0026ndash;97. https://doi.org/10.1002/2014WR016862.\u003c/li\u003e\n\u003cli\u003eGurnell AM, Bertoldi W, Corenblit D. Changing River Channels: The Roles of Hydrological Processes, Plants and Pioneer Fluvial Landforms in Humid Temperate, Mixed Load, Gravel Bed Rivers. Earth Sci Rev 2012;111:129\u0026ndash;41. https://doi.org/10.1016/j.earscirev.2011.11.006.\u003c/li\u003e\n\u003cli\u003eCorenblit D, Piegay H, Arrignon F, Gonzalez-Sargas E, Bonis A. Interactions between vegetation and river morphodynamics. Part I: Research clarifications and challenges. Earth Sci Rev 2024;253. https://doi.org/10.1016/j.earscirev.2024.104769.\u003c/li\u003e\n\u003cli\u003eHuai W, Li S, Katul GG, Liu M, Yang Z. Flow dynamics and sediment transport in vegetated rivers: A review. Journal of Hydrodynamics 2021;33:400\u0026ndash;20.\u003c/li\u003e\n\u003cli\u003eBejarano MD, Sordo-Ward A, Garrote L, Garc\u0026iacute;a J. Riparian vegetation metrics as tools for guiding ecological restoration in riverscapes. Knowl Manag Aquat Ecosyst 2011;402:21. https://doi.org/10.1051/kmae/2011075.\u003c/li\u003e\n\u003cli\u003eGran K, Paola C. Riparian vegetation controls on braided stream dynamics. Water Resour Res 2001;37:3275\u0026ndash;83. https://doi.org/10.1029/2000WR000203.\u003c/li\u003e\n\u003cli\u003eNaiman RJ, Decamps H. The ecology of interfaces: riparian zones. Annu Rev Ecol Syst 1997;28:621\u0026ndash;58. https://doi.org/10.1146/annurev.ecolsys.28.1.621.\u003c/li\u003e\n\u003cli\u003eSakio H. Effects of natural disturbance on the regeneration of riparian forests in mountainous regions in Japan. Plant Ecol 1997;132:181\u0026ndash;95. https://doi.org/10.1023/A:1009772119318.\u003c/li\u003e\n\u003cli\u003eMerritt DM, Poff NL. Shifting dominance of key drivers of riparian vegetation composition along a prairie-to-montane river network. Ecology 2010;91:1645\u0026ndash;58. https://doi.org/10.1890/09-0 shifting.\u003c/li\u003e\n\u003cli\u003eSong U, Kim D, Lee EJ, Balke T, Bouma TJ. Life-History Plasticity of Riparian Annual Plants Adapted to Extreme Variations in Water Level: Mesocosm Experiments. PLoS One 2016;11. https://doi.org/10.1371/journal.pone.0147551.\u003c/li\u003e\n\u003cli\u003eDixon MD, Turner MG, Naiman RJ. The influence of local and landscape-scale factors on the distribution of pioneer tree seedlings on the Wisconsin River, USA. Ecosystems 2002;5:369\u0026ndash;83. https://doi.org/10.1007/s10021-001-0083-9.\u003c/li\u003e\n\u003cli\u003eTabacchi E, Lambs L, Guilloy H, Planty-Tabacchi AM, Muller E, Decamps H. The role of riparian vegetation in the ecological integrity of alluvial rivers. Freshw Biol 1998;40:609\u0026ndash;23. https://doi.org/10.1046/j.1365-2427.1998.00421.x.\u003c/li\u003e\n\u003cli\u003eKim D, Yu J, Lee S, Kang T, Cho KH. Spatial Distribution of Vegetation on Stream Bars and the Riparian Zone Reflects Successional Pattern Due to Fluid Dynamics of River. Water (Basel) 2023;15:1493. https://doi.org/10.3390/w15081493.\u003c/li\u003e\n\u003cli\u003eMahoney JM, Rood SB. Streamflow requirements for cottonwood seedling recruitment\u0026mdash;an integrative model. Wetlands 1998;18:634\u0026ndash;45. https://doi.org/10.1007/BF03161678.\u003c/li\u003e\n\u003cli\u003eHortob\u0026aacute;gyi B, Corenblit D, Vautier F, Steiger J, Roussel E. Riparian Vegetation and Sediment Supply on the Morphodynamic Response of an Experimental Stream to Floods. Front Environ Sci 2019;7:40. https://doi.org/10.3389/fenvs.2019.00040.\u003c/li\u003e\n\u003cli\u003eZhang Y, Wang X, Liu X. Effects of Patch Properties of Submerged Vegetation on Sediment Scouring and Deposition. Water (Basel) 2024;16:2144. https://doi.org/10.3390/w16152144.\u003c/li\u003e\n\u003cli\u003eCalvani G, Francalanci S, Solari L. A Physical Model for the Uprooting of Flexible Vegetation on River Bars. Water Resour Res 2019;55:4674\u0026ndash;90. https://doi.org/10.1029/2018WR024268.\u003c/li\u003e\n\u003cli\u003eYagci O, Celik F, Kitsikoudis V, Koken M. Experimental study on influence of different patterns of an emergent vegetation patch on the flow field and scour/deposition processes in the wake region. Water Resour Res 2023;59. https://doi.org/10.1029/2023WR034978.\u003c/li\u003e\n\u003cli\u003eWang X, Li S, Yang Z, Huai W. Incipient sediment motion in vegetated open-channel flows predicted by critical flow velocity. Journal of Hydrodynamics 2022;34:63\u0026ndash;8.\u003c/li\u003e\n\u003cli\u003eLi S, Huai W, Vyawahare R. Review of the effect of river vegetation on sediment transport and river morphology and erosion prevention. Journal of Hydrodynamics 2025. https://doi.org/10.1007/s42241-024-0065-z.\u003c/li\u003e\n\u003cli\u003eVannoppen W, vanmaercke M, De Baets S, Poesen J. How do root and soil characteristics affect the erosion-reducing potential of plant species? Plant Soil 2017;419:1\u0026ndash;18. https://doi.org/10.1007/s11104-017-3301-4.\u003c/li\u003e\n\u003cli\u003eDe Baets S, Poesen J, Gyssels G, Knapen A. Impact of root architecture on the erosion-reducing potential of roots during concentrated flow. Earth Surf Process Landf 2008;33:1323\u0026ndash;45. https://doi.org/10.1002/esp.1470.\u003c/li\u003e\n\u003cli\u003eEdmaier K, Burlando P, Perona P. Mechanisms of vegetation uprooting by flow in alluvial non-cohesive sediment. Hydrol Earth Syst Sci 2011;15:1615\u0026ndash;27. https://doi.org/10.5194/hess-15-1615-2011.\u003c/li\u003e\n\u003cli\u003evan de Lageweg WI, Veenstra JL, van der Lee GEM, Hulscher SJMH. Processes and parameters underlying the failure of salt marsh vegetation in different sediments. University of Twente; 2022.\u003c/li\u003e\n\u003cli\u003ePerona P, Crouzy B, Molnar P, Dudun A, Vetsch D, Burlando P. Resilience of riverbed vegetation to uprooting by flow. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 2018;474. https://doi.org/10.1098/rspa.2017.0547.\u003c/li\u003e\n\u003cli\u003eBywater‐Reyes S, Wilcox AC, Stella JC, Lightbody AF. Flow and scour constraints on uprooting of pioneer woody seedlings. Water Resour Res 2015;51:9190\u0026ndash;206.\u003c/li\u003e\n\u003cli\u003eKleinhans MG, McMahon WJ, Davies NS. What even is a meandering river? A philosophy-enhanced synthesis of multilevel causes and systemic interactions contributing to river meandering. Geological Society, London, Special Publications, vol. 540, 2024. https://doi.org/10.1144/SP540-2022-218.\u003c/li\u003e\n\u003cli\u003eLightbody AF, Kui L, Stella JC, Skorko KW, Bywater-Reyes S, Wilcox AC. Riparian vegetation and sediment supply regulate the morphodynamic response of an experimental stream to floods. Front Environ Sci 2019;7:40.\u003c/li\u003e\n\u003cli\u003eSidle RC, Ochiai H. Landslides: Processes, Prediction, and Land Use. American Geophysical Union; 2006. https://doi.org/10.1029/GM160.\u003c/li\u003e\n\u003cli\u003eOhtsuka S, Sato Y, Yoshikawa T, Sugii T, Kodaka T, Maeda K. Levee damage and revetment erosion by the 2019 Typhoon Hagibis in the Chikuma River, Japan. Soils and Foundations 2021;61:1172\u0026ndash;88.\u003c/li\u003e\n\u003cli\u003eCalvani G, Francalanci S, Solari L. Insights into the dynamics of vegetated alternate bars by means of flume experiments. Water Resour Res 2023;59. https://doi.org/10.1029/2022WR032536.\u003c/li\u003e\n\u003cli\u003eGeng X, Cao W, Liu C, Zhang G. Experimental Study of Bedform Development Characteristics and Their Effects on Sediment Transport. Applied Sciences 2024;14:9823.\u003c/li\u003e\n\u003cli\u003eCrosato A, Mosselman E, Beidmariam Desta F, Uijttewaal WSJ. Experimental and numerical evidence for intrinsic nonmigrating bars in alluvial channels. Water Resour Res 2011;47.\u003c/li\u003e\n\u003cli\u003eHabib S, Tanaka N. Effect of Vegetation Type and Location on the Change of Alternate Sandbars in a Straight River Channel. International Journal of Civil Engineering 2025. https://doi.org/10.1007/s40999-025-01118-9.\u003c/li\u003e\n\u003cli\u003eRominger JT, Lightbody AF, Nepf HM. Effects of added vegetation on sand bar stability and stream hydrodynamics. Journal of Hydraulic Engineering 2010;136:994\u0026ndash;1002.\u003c/li\u003e\n\u003cli\u003eZong L, Nepf H. Spatial distribution of deposition within a patch of vegetation. Water Resour Res 2011;47.\u003c/li\u003e\n\u003cli\u003eKUROKI M, KISHI T. Regime criteria on bars and braids in alluvial straight channels. Proceedings of the Japan Society of Civil Engineers, vol. 1984, Japan Society of Civil Engineers; 1984, p. 87\u0026ndash;96.\u003c/li\u003e\n\u003cli\u003eWong M, Parker G. Reanalysis and correction of bed-load relation of Meyer-Peter and M\u0026uuml;ller using their own database. Journal of Hydraulic Engineering 2006;132:1159\u0026ndash;68.\u003c/li\u003e\n\u003cli\u003eLanzoni S. Experiments on bar formation in a straight flume: 2. Graded sediment. Water Resour Res 2000;36:3351\u0026ndash;63.\u003c/li\u003e\n\u003cli\u003eKleinhans MG, van Dijk WM, van de Lageweg WI, Hoyal DCJD, Markies H, van Maarseveen M, et al. Quantifiable effectiveness of experimental scaling of river- and delta morphodynamics and stratigraphy. Earth Sci Rev 2014;133:43\u0026ndash;61. https://doi.org/10.1016/j.earscirev.2014.03.001.\u003c/li\u003e\n\u003cli\u003eShahmohammadi R, Afzalimehr H, Sui J. Assessment of critical shear stress and threshold velocity in shallow flow with sand particles. Water (Basel) 2021;13:994.\u003c/li\u003e\n\u003cli\u003ePostma G, Kleinhans MG, Meijer PT, Eggenhuisen JT. Sediment transport in analogue flume models compared with real‐world sedimentary systems: A new look at scaling evolution of sedimentary systems in a flume. Sedimentology 2008;55:1541\u0026ndash;57.\u003c/li\u003e\n\u003cli\u003eRedolfi M, Welber M, Carlin M, Tubino M, Bertoldi W. Morphometric properties of alternate bars and water discharge: A laboratory investigation. Earth Surface Dynamics 2020;8:789\u0026ndash;808. https://doi.org/10.5194/esurf-8-789-2020.\u003c/li\u003e\n\u003cli\u003eCrosato A, Mosselman E. Simple physics-based predictor for the number of river bars and the transition between meandering and braiding. Water Resour Res 2009;45. https://doi.org/10.1029/2008WR007242.\u003c/li\u003e\n\u003cli\u003eZong L, Nepf H. Spatial distribution of deposition within a patch of vegetation. Water Resour Res 2011;47. https://doi.org/10.1029/2010WR009516.\u003c/li\u003e\n\u003cli\u003eBywater-Reyes S, Diehl RM, Wilcox AC. The influence of a vegetated bar on channel-bend flow dynamics. Earth Surface Dynamics 2018;6:487\u0026ndash;503. https://doi.org/10.5194/esurf-6-487-2018.\u003c/li\u003e\n\u003cli\u003eGong M, Wu G, Du S. Laboratory Study of Local Scour Around an Array of Pile Groups in Clear-Water Scour Conditions. J Mar Sci Eng 2025;13:137. https://doi.org/10.3390/jmse13010137.\u003c/li\u003e\n\u003cli\u003eYagci O, \u0026Ouml;zgur Kirca VS, Kitsikoudis V, Wilson CAME, Celik MF, Sertkan C. Experimental study on influence of different patterns of an emergent vegetation patch on the flow field and scour/deposition processes in the wake region. Water Resour Res 2024;60:e2023WR034978.\u003c/li\u003e\n\u003cli\u003eWickramasinghe R, Tanaka N. Investigation of hydrodynamics along an embankment generated by a nearby riparian vegetation patch. Landscape and Ecological Engineering 2023;19:179\u0026ndash;97.\u003c/li\u003e\n\u003cli\u003eSmith RD, Sidle RC, Porter PE, Noel JR. Effects of experimental removal of woody debris on the channel morphology of a forest, gravel-bed stream. J Hydrol (Amst) 1993;152:153\u0026ndash;78.\u003c/li\u003e\n\u003cli\u003eRedolfi M, Musa M, Guala M. On steady alternate bars forced by a localized asymmetric drag distribution in erodible channels. J Fluid Mech 2021;916. https://doi.org/10.1017/jfm.2021.122.\u003c/li\u003e\n\u003cli\u003eCaroppi G, V\u0026auml;stil\u0026auml; K, J\u0026auml;rvel\u0026auml; J, Lee C, Ji U, Kim HS, et al. Flow and wake characteristics associated with riparian vegetation patches: Results from field‐scale experiments. Hydrol Process 2022;36:e14506.\u003c/li\u003e\n\u003cli\u003eMontgomery DR, Buffington JM. Channel-reach morphology in mountain drainage basins. Geol Soc Am Bull 1997;109:596\u0026ndash;611.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-hydrodynamics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ijhd","sideBox":"Learn more about [Journal of Hydrodynamics](http://link.springer.com/journal/42241)","snPcode":"42241","submissionUrl":"https://www.editorialmanager.com/ijhd/default2.aspx","title":"Journal of Hydrodynamics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Vegetation dynamics, sandbar morphology, vegetation uprooting, erosion, deposition.","lastPublishedDoi":"10.21203/rs.3.rs-7909292/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7909292/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eVegetation fundamentally regulates river-bar morphology, yet how bars respond when vegetation is progressively removed remains poorly understood. Flume experiments under two steady flows using a two-stage protocol were conducted: Stage 1 trimmed about 30% from the leading edge of an apex patch; Stage 2 cleared the remainder. Bed evolution was analyzed using depth-normalized relief, areal aggradation-degradation fractions, lateral mass-balance indices metrics, and thalweg-based wavelength. Partial removal (Stage 1) triggered an abrupt morphodynamic transition: bed aggradation surged from 20\u0026ndash;25% to 56\u0026ndash;77%, marking a threshold shift from scour-dominated to deposition-dominated conditions and reorganizing the entire bar\u0026ndash;wake system. Complete removal (Stage 2) stabilized this configuration, with deposition remaining dominant and the flow wake lengthening and reattaching farther downstream. At higher discharge, bar wavelength expanded by ~\u0026thinsp;10\u0026ndash;59%, reflecting longer wakes and reduced roughness, while the lower discharge mainly deepened local relief without major re-spacing. Morphodynamically, Stage 1 acts as the trigger, converting a forced, asymmetric deflector bar into a diffusively depositional form; Stage 2 acts as the stabilizer, allowing the reach to relax toward a free-bar template governed by intrinsic flow\u0026ndash;sediment dynamics. Practically, these findings highlight that partial vegetation loss can induce threshold instability, creating scour hotspots. In contrast, complete clearing tends to redistribute sediment more evenly and stabilize bar spacing\u0026mdash;offering direct guidance for river restoration and vegetation-management design.\u003c/p\u003e","manuscriptTitle":"A Nonlinear State Shift: Morphodynamic Thresholds During Progressive Vegetation Uprooting on Alternate Bars","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-10 23:52:53","doi":"10.21203/rs.3.rs-7909292/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2025-10-30T11:05:46+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-10-30T10:35:19+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-10-29T09:36:53+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Hydrodynamics","date":"2025-10-26T21:33:03+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-hydrodynamics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"ijhd","sideBox":"Learn more about [Journal of Hydrodynamics](http://link.springer.com/journal/42241)","snPcode":"42241","submissionUrl":"https://www.editorialmanager.com/ijhd/default2.aspx","title":"Journal of Hydrodynamics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"dc6a0618-dac6-4108-81db-b9ac4cd3648a","owner":[],"postedDate":"November 10th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-01-10T04:41:13+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-10 23:52:53","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7909292","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7909292","identity":"rs-7909292","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}