Multi-tracer baseflow estimation and topographic controls on stream water transit times in a humid tropical experimental catchment

2025 · doi:10.22541/au.176433331.13692152/v1
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This study used multi-tracer methods to estimate baseflow contributions and identify topographic influences on stream water transit times within a humid tropical experimental catchment.

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This (preprint) study used monthly samples of river water, groundwater, and rainwater from the Vamanapuram humid tropical experimental catchment (May 2022–April 2024) to characterize spatial and seasonal variability of baseflow contributions and estimate mean river-water transit times. Using a two-component mass-balance hydrograph separation approach (classical hydrograph separation, CHS) and a correlation-based ensemble approach (EHS), the authors found that CHS and EHS gave similar baseflow fractions, but EHS was favored due to reduced uncertainty; they also reported that electrical conductivity tracer estimates were lower than those from silicate and stable isotopes (δ¹⁸O, δ²H), with isotopic methods showing higher uncertainty. Estimated baseflow comprised more than half of streamflow across seasons and locations, while transit times ranged from 45 to 143 days and were mainly controlled by topography (watershed elevation and slope), alongside heterogeneous well behavior suggesting variable replenishment. The paper does not explicitly discuss endometriosis or adenomyosis; it was included in the corpus via a keyword match in the upstream search index.

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Abstract

The Vamanapuram experimental catchment has been established in a humid tropical setting, where the hydrological processes are poorly characterized and have received limited attention. The Monthly River water, groundwater, and rainwater samples have been collected from May 2022 to April 2024 to understand the spatial and seasonal variability of baseflow contributions. The Chemical (Electrical conductivity, silicate) and isotopic tracers (δ 18 O, δ 2 H) have been used to estimate the baseflow contribution (and associated uncertainty) and the mean transit time of river water. The two-component Classical Hydrograph Separation (CHS, mass balance-based) and the recent Ensemble Hydrograph Separation (EHS, correlation-based) have been used to quantify baseflow contributions. Although CHS and EHS resulted in almost similar baseflow contributions, but EHS is recommended due to reduced uncertainty. Estimated baseflow contributions using EC as a tracer are significantly lower than those estimated using other tracers. Estimates based on silicate, δ 18 O, and δ 2 H are also generally comparable, and isotopic tracers have a higher degree of uncertainty in estimates than chemical tracers, silica can be used as alternate tracer for baseflow estimation. The baseflow is found to be dominant contributor to streamflow (irrespective of season and location) with fraction greater than 0.5. Mean transit time of stream water ranges between 45 and 143 days, mainly controlled by topography (mean watershed elevation and slope). The groundwater wells found to be behave differently, indicating either seasonal replenishment by rainfall, or steady state or lack of replenishment and diminishing potential of wells. The Trend analysis of groundwater stable isotopic data, and levels indicated that parts of catchment are not getting replenished by rainfall, and groundwater resources are at risk, and needs immediate urgent attention.
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Abstract

The Vamanapuram experimental catchment has been established in a humid tropical setting, where the hydrological processes are poorly characterized and have received limited attention. The Monthly River water, groundwater, and rainwater samples have been collected from May 2022 to April 2024 to understand the spatial and seasonal variability of baseflow contributions. The Chemical (Electrical conductivity, silicate) and isotopic tracers (δ 18 O, δ 2 H) have been used to estimate the baseflow contribution (and associated uncertainty) and the mean transit time of river water. The two-component Classical Hydrograph Separation (CHS, mass balance-based) and the recent Ensemble Hydrograph Separation (EHS, correlation-based) have been used to quantify baseflow contributions. Although CHS and EHS resulted in almost similar baseflow contributions, but EHS is recommended due to reduced uncertainty. Estimated baseflow contributions using EC as a tracer are significantly lower than those estimated using other tracers. Estimates based on silicate, δ 18 O, and δ 2 H are also generally comparable, and isotopic tracers have a higher degree of uncertainty in estimates than chemical tracers, silica can be used as alternate tracer for baseflow estimation. The baseflow is found to be dominant contributor to streamflow (irrespective of season and location) with fraction greater than 0.5. Mean transit time of stream water ranges between 45 and 143 days, mainly controlled by topography (mean watershed elevation and slope). The groundwater wells found to be behave differently, indicating either seasonal replenishment by rainfall, or steady state or lack of replenishment and diminishing potential of wells. The Trend analysis of groundwater stable isotopic data, and levels indicated that parts of catchment are not getting replenished by rainfall, and groundwater resources are at risk, and needs immediate urgent attention. Information & Authors Information Version history Copyright This work is licensed under a Non Exclusive No Reuse License.

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Authors Metrics & Citations Metrics Article Usage 164views 107downloads Citations Download citation Rajat Kumar Sharma, Muddu Sekhar, RDDeshpande, et al. Multi-tracer baseflow estimation and topographic controls on stream water transit times in a humid tropical experimental catchment. Authorea. 28 November 2025. DOI: https://doi.org/10.22541/au.176433331.13692152/v1 DOI: https://doi.org/10.22541/au.176433331.13692152/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu.

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