Assessment of Excess Abstraction Impacts by Pivot Irrigation on Ground Water Quantity in Shendi Sub-basin, Sudan

Assessment of Excess Abstraction Impacts by Pivot Irrigation on Ground Water Quantity in Shendi Sub-basin, Sudan | 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 Assessment of Excess Abstraction Impacts by Pivot Irrigation on Ground Water Quantity in Shendi Sub-basin, Sudan Iman Gibreel, Adil Elkrail This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4901377/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The hydrogeological system, in the study area, consists of two aquifers, namely; shallow and deep aquifer. These aquifers show a wide range of variable hydraulic parameters, due to rapid lateral and vertical changes of Facies. The deep aquifer is characterized by higher hydraulic parameters, large volume and, consequently, higher productivity compared to the shallow aquifer. These valuable resources are threatened by the impacts of accelerated overexploitation and flood irrigation practices, and may be severely over drafted or may be subjected to continuous decaling of water level and water quality degradation if not managed properly. Previous geological and hydrogeological studies have established that significant overexploitation influence the flow characteristics and water quality, which influence the possibility of using groundwater as a main water resource. The conceptual hydrogeological model was developed using Visual MODFLOW software to assess the impact of pivotal irrigation on groundwater potentiality in shendi sub-basin. Numbers of scenarios were performed to study the impact of well discharge increasing rates to drawdown, subsurface Inflow, Outflow through the general head boundaries (GHBs) at the model domain of Shendi sub- Basin. The results of simulation indicated that increasing wells’ pumping rate to meet future demand will likely result in more dramatic declines in groundwater level with maximum drawdown of 13.39 m. The piezometric surface measured at two adjacent wells before and after pivotal irrigation period, showed a drop of 10m in the groundwater level. Mearements of ground water levels after the pivotal irrigation period show a clear decline ranging from 3 m near the Nile to 10 m at the middle of the area (Maaqil area), and increases eastwards up to 15 m (Bir Al-Jud, 30 Km from east of the river Nile. Most of the wells are exposed to depletion during the pivotal irrigation periods as in Elgemma agricultural project. The most significant impacts of pivotal irrigation in the study area are the ecological damage such as severe reduction in groundwater storage which led to the depletion of wells in agricultural projects which affected the human and vegetation activities in the region. Additionally, it results in insufficient drinking, industrial, and municipal water supplies, which significantly change the ecosystem. Pivotal irrigation system conceptual model MODFLOW aquifer hydraulic parameters Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction Uncontrolled groundwater pumping has caused dramatic changes to our natural landscape. Over- pumping causes severe decline in the water table, resulting in depletion of the streams wetland and land subsidence along rivers, resulting in the destruction of highly productive ecosystems. Irrigation systems also have an indirect impact on the surrounding environment. These indirect effects may not be immediately noticeable as the direct issues. These effects take a longer time to develop and produce longer-lasting changes. In the study area, the main source of water supply for pivotal irrigation projects is the underground reservoir for the extension of agricultural projects away from the Nile River, which makes the specter of depletion loom in far distance due to over-pumping and lack of surface recharge sources (Elkrail, et al 2019 ). Moreover, the current situation in Shendi-basin threatens the life of the human communities, the ecosystem and warns of a significant drop in the groundwater level and the depletion of many wells on the edges of the basin, causing human displacement and the loss of many land and agricultural crops. The main objects of this study are to determine the hydrogeological characteristics of the aquifer, calculate the amount of water input, output (water balance) and the storage, as well as estimate the drop in the water level and develop a predictive scenario to avoid depletion risks, Groundwater Flow Model soft ware was used as an appropriate way to do so. 2. Characteristics of the Study Area The area of study comprises the upper part of Shendi –Atbara basin, namely Shendi Formation which is located in the River Nile State, north- central Sudan at about 180Km North of Khartoum. The area lies between latitudes 16º 15`17.7" - 16º 1`15.6" N and longitudes 33º 10`57.8" - 33º 45`33.85" E. (Fig.1). The study area is a rugged, highly undulated. The hilly terrain is characterized by relatively steep slope toward the east and gentle one to the west toward the River Nile. The fecundity of such areas is due to the effective conjunctive use of surface water from the Nile river and ground water from both the Nile Valley Aquifer (NVA) and Nubian Sandstone Aquifer (NSA) that under lies the region. Historically, farmers in river Nile state relied on the Nile flood pulse to inundate basins which are extensive, flat areas separated from the Nile Valley extended over 20 km from the riverbank in some places. The widespread flooding recharged the aquifers, which were used for supplemental irrigation (Fragaszy & Closas 2016). Groundwater continued to be used alongside the large increase in surface irrigation to ensure the survival of both perennial crops and staples during low-flood years (Bacon 1948). The River Nile dominates the drainage of the area and represents active locales levels of erosion. North of Khartoum the River Nile flows and cuts centrally through the only upstanding ground formed by Sabaloka Ring Complex. There are number of seasonal water courses that drain to the Nile. Drainage patterns are one of the most important indicators used in the investigation of hydrogeological features. The drainage system is greatly influenced by foliation, faults, and joints of the underlying rocks but on the whole is dendritic drainage pattern. Due to the presence of high and low angle topographic feature beside each other the drainage pattern is in the form of valleys that flow west or northwest towards the River Nile. The most famous one is Wadi Awatieb near to El-Moswarat and Wadi Almocabrab. The study area occupy south of the Central Africa Shear Zone (CASZ). The geology of the southern area is dominated by basement complex rocks. The Basement complex in the study area is affected by tectonic activities, which resulted into widely distributed joints, faults, foliations and folds. The area is characterized by two major rock associations' namely; metamorphic and plutonic igneous rocks, which include acidic character. Metamorphic rocks represent the oldest rock group in the area consist of granitic- gneisses, gneisses, Schists and Quartzite respectively. The following geological units have been distinguished in the study area and are arranged from top to bottom (Delany 1954, Almond 1982, Vail 1974, Kroner, et al 1987, & Sadig, Farwa 1989) (Fig2): Superficial Deposits Nubian Sandstone Formation. Basement Complex. The Nubian sandstone (Cretaceous Sedimentary Rocks) covers 28% of the area of the Sudan and is most important aquifer in the country. It covers together with the basement complex, about78% of the Sudan (Whiteman 1971) 3. Methodology and Model Construction The objectives of this study are to evaluate the groundwater flow system in the study area based on determination of the aquifer characteristics, groundwater flow dynamic, and storage capacity of the aquifers and groundwater balance of the area using groundwater model techniques (Visual MODFLOW code). The main input data for model design in the study area that collected and observed from the field work and calculated with relevant methods include: aquifer types, observation wells, pumping wells, recharge sources, aquifer hydraulic properties, initial head and boundary conditions. There are two type of water bearing layers in Shendi basin, upper layer is alluvial aquifer (recent deposits). It is unconfined with high permeability and good water quality. The lower layer is Nubian sand stone aquifer (Cretaceous sediments) is characterized by good hydraulic properties and fresh water quality. The main aquifer materials are unconsolidated sediments layers of Cretaceous deposits. In the lower reach, the aquifer thickness ranges from 50–125 m with extreme maximum thickness of 135 meters. The depth to groundwater table is about 10 to 37 m below the surface and the average depth to basement is 220 m from the surface. For aquifer hydraulic properties, the hydraulic conductivity, specific coefficient, storage coefficient, effective porosity and total porosity were measured with relevant methods for upper and lower aquifer in the model domain. The unconsolidated alluvial aquifers at the upper, varies in thickness from30 to 65 m. and depth to water table is 10–35 m. The hydraulic conductivity is 1.5–15 m/d. The specific storage (Ss) is 0.0004, specific coefficient (Sy) is 0.24, effective porosity (ne) is 0.27 and total porosity (nt) is 0.31. The Nubian sandstone aquifers at the lower, varies in thickness from 50 to 95 m. The hydraulic conductivity is 1.8–18 m/d. The storage coefficient (Ss) is 0.00005, specific coefficient (Sy) is 0.25, effective porosity (ne) is 0.27 and total porosity (nt) is 0.31. Based on the boundary conditions, the bottom of the aquifers and the western side of the model area were considered as no-flow boundaries. The top of the aquifers is considered as the variable head boundary. The southern, eastern and northern sides of the model domain were taken as general head boundary (GHB), whereas, the northwestern part was taken as river boundary (Fig. 3). Generally, mathematical model consists of governing equations, boundary conditions and initial conditions. Boundary conditions are mathematical statements specifying the dependent variable (head) or the derivative of dependent variable (flux) at the boundary of the model domain. The boundary conditions express the way the considered domain interacts with its environment. The upper surface of the aquifer represents a flow boundary, where water can enters and leaves the aquifer; through the unconfined layer i.e. water table condition. Therefore, the flow has irregular and random behavior. The top of the aquifer is considered as the variable head boundary, where flow may enter the model as a recharge from the River Nile seasonal stream and direct precipitations. The southern, eastern and northern sides of the model were taken as General Head Boundary (GHB) of 390, 380 and 388 m, above sea level (m, a.s.l) respectively for upper aquifer, whereas GHB of 328, 322 and 321(m, a. s. l) were assigned to the southern, eastern and northern sides of lower aquifer respectively and Boundary conductance is 6500m2/d. The western side of the model area was assigned as river boundary, along the River Nile course. The hydraulic conductivity of 1.5–15, the specific coefficient of 0.24, storage coefficient of 0.0004, effective porosity of 0.27 and total porosity of 0.31 were assigned to the upper aquifer. On the other hand, hydraulic conductivity of 1.8–18 m\d, the specific storage of 0.25, storage coefficient of 0.00005, effective porosity of 0.27 and total porosity of 0.31were assigned to the lower aquifer for model simulation. The measured heads in the observation wells were used as initial head distribution for the model simulation. The bo5ttom of the aquifer and the western side of the model area were considered as no-flow boundaries. The top of the aquifer is considered as the variable head boundary, where flow may enter the model as a recharge from the River Nile seasonal stream and direct precipitations. The southern, eastern and northern sides of the model were taken as General Head Boundary (GHB) of 390, 380 and 375 m, above sea level (m, a.s.l) respectively for upper aquifer, whereas GHB of 388, 370 and 365 (m, a.s.l) were assigned to the southern, eastern and northern sides of lower aquifer respectively. The western side of the model area was assigned as river boundary, along the River Nile course. 4. Results and Discussion From the piezometric surface map Fig. (4), the general flow direction is from the west to the east and northeast, confirming the natural aquifer recharge from the River Nile which is one of the model credibility. Semi-cone of depression was observed at the center of the area due to heavy pumping for agricultural activities (pivotal irrigation) at these areas (Elkrail, et al 2014 ). The zone budget was calculated for steady state model simulation for the whole model domain (Table). The volume of water in cubic meter per day (m3/d) and its percentage was calculated for each component of the hydrologic budget. Recharge is the most important hydrologic component of inflow to the aquifer, which is able to offset the groundwater extraction from the aquifer. The total volume of the aquifer inflow is (1305381m 3 /day), while the total volume of the aquifer outflow is 1304902m 3 /day (Table 5.1). Groundwater pumping volume through production wells in the entire area computed by the model represents 54% of the total outflow from the aquifer. The subsurface inflow through the GHB represents 14.4% from the total inflow. The river recharge to the aquifer as subsurface inflow represents 29.7% of the total inflow. The recharge water volume from direct precipitation represents 55.9% of the total inflow. The subsurface outflow through the GHB from the aquifer represents 40.5% from the total outflow. Finally, the discrepancy between inflow and outflow amount to 478 m3/day as daily water reserve. Numbers of scenarios were performed to study the impact of well discharge increasing rates to drawdown, subsurface Inflow, Outflow through the GHBs at the model domain of Shendi sub- Basin (Table 4.). The Projected Growth Scenario simulates increased groundwater discharge to meet water demands due to the rapid population and agricultural activities growth. The incremental percentage rate of wells discharge in study area by 20%, 40%, 60%, 80%, and 100% from the original pumping rate were simulated Table (5.2). Groundwater subsurface flow (inflow & outflow) was quantified by MODFLOW simulation as GHB condition. The resultant increasing drawdown and subsequent increasing subsurface inflow and decreasing subsurface out flow through GHB were reported. The results of simulation indicate that increased wells’ pumping to meet future demand will likely result in more dramatic declines in groundwater levels with maximum drawdown of 13.39 m (Table 2) and relatively increasing subsurface inflow and decreasing subsurface out flow. The data of the wells drilled in the period before the establishment of pivot irrigation projects were studied and compared with the neighboring wells drilled at a later time for pivot irrigation until the year 2020, showing a significant drop in the ground water level, which exposes many wells to depletion. The water level measured at two adjacent wells before and after the pivotal irrigation period, show considerable drop in the piezometric surface in the area., Clear drop of water level was monitored ranging from 3 meters near the Nile to 10 meters at the middle of the area ( Maaqil area), and the decline increases east up to 15 meters in the far east (Bir Al-Jud) at 30 km from the Nile. The half_ life of the well is shortened and exposed to depletion quickly, as in Elgemma agricultural project Table (3). In a number of agricultural projects in the eastern direction (28 km far to the River Nile (Elgemma Agriculture Project) outskirts of the basin monitored the depletion of a number of wells as in the agricultural summit projects, in this case annually one well at least faced the threat of depletion, static water level was withdrawal with the value exceed 9–12 m in some locations Table (3). Figure (5) shows dramatic change in piezometric level in different localities with minor change in drawdown (dd). In the central part of the basin and towards the Nile River, the depth to water level decreases up to the river bank. Before a pivotal irrigation activities, the depth to water level ranged from 11m to 27m far east of the River Nile with an average of 18.3 m, While the water levels reached the range from 12 to 38 m with an average of 27.5 after pivotal irrigation activities, coinciding with deterioration in the amount of water replenishment for the aquifers in the basin. One of the most significant causes of ecological damage in the study area is the reduction of groundwater storage which led to wells depletion in agricultural projects which reflected on human activity and vegetation in the region. Moreover, the reduction of groundwater storage due to mismanagement of pivotal irrigation, results in insufficient drinking, industrial, and municipal water supplies, which significantly change the ecosystem. To reduce the impact of the pivotal irrigation activities good relevant management scenarios should be conducted in the study area. The results of simulation indicate that increased wells’ pumping to meet future demand will likely result in even more dramatic declines in groundwater levels. Declarations Acknowledgement The authors appreciate the outstanding logistical and technical support provided by Ministry of Water Resources and Irrigation T hey also acknowledge the El Neelain University for vital support. References Elkrail, A.B., Amin Dafalla and Mohamed Adlan (2019): Numerical Simulation of Groundwater Flow in Shendi Sub-Basin, Sudan. Fragaszy and Closas (2016): Irrigation expansion in Northern State, Sudan, pp.158 Bacon, G. (1948): Crops of the Sudan. In Tothill, J. (Ed), Agriculture in the Sudan: Being a handbook of agriculture as practiced in the Anglo-Egyptian Sudan, pp. 302-400. Oxford: Oxford University Press. Delany, F. M., (1954):Recent contribu- tions to the geology of the Sudan. Ninteenth int. Geol. Congr. Algiers, 20: 11-18. Almond, D. C., (1982): New ideas on the geological history of the Basement Complex of NE Sudan. Sudan Note and Rec. 59: 106136. Vail, J.R., (1974):. Distribution of the Nubian Sandstone Formation in Sudan and vicinity. AAPG Bulletin, 58, 10251036. Kröner, A., Greiling, R., Reischmann, T., Hussein, I. M., Stern, R. J., Durr, S. and Zimmer, M., (1987a): Pan-African crustal evolution in the segment in the northern Africa. In: Kro¨ner, A. (Ed.), Proterozoic Lithosphere Evolution. International Lithosphere Program Publication 130. American Geophysical Union Geodynamics Series, Washington, DC. 17: 235–257. Sadig and Farwa (1989).Delineat the Umm Marahik basin and its bounding faulted contact in Sabaloka area. They confirmed the general condition that the gravity method is a useful tool in the exploration of groundwater. ( 9) Whiteman, A. J. (1971): The geology of the Sudan Republic. Clarendon Press, Oxford, 299 pp. Elkrail, A. , Awad, T. Yousif, Y. (2014). Numerical simulation of groundwater flow in southeast of el Damer town, river Nile state, Sudan, American Journal of Earth Sciences 2014; 1(1): 21-24. Tables Tables 1 to 3 are available in the Supplementary Files section Additional Declarations No competing interests reported. Supplementary Files ListofTables.docx Cite Share Download PDF Status: Posted Version 1 posted 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4901377","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":343043588,"identity":"57d1863a-9aa2-4ba8-add2-75a33c5b9923","order_by":0,"name":"Iman Gibreel","email":"","orcid":"","institution":"University of Khartoum","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Iman","middleName":"","lastName":"Gibreel","suffix":""},{"id":343043591,"identity":"afbc4731-9116-4f94-b26a-bc1efb970d59","order_by":1,"name":"Adil 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14:49:32","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4901377/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4901377/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":64222231,"identity":"8e007f39-4c94-4145-9c3c-13f774487ce6","added_by":"auto","created_at":"2024-09-10 12:21:48","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":72645,"visible":true,"origin":"","legend":"\u003cp\u003eLocation map of the study area\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4901377/v1/1461620dc3e84c00c07e7069.png"},{"id":64222232,"identity":"283a6bae-8c3e-4574-b20b-cacef357dcc2","added_by":"auto","created_at":"2024-09-10 12:21:48","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":374691,"visible":true,"origin":"","legend":"\u003cp\u003eGeological Map of the Study Area\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4901377/v1/4e1d973779785520a1dc3cfc.png"},{"id":64222235,"identity":"9599dd99-d26d-4bdf-836f-1bd56d0082ef","added_by":"auto","created_at":"2024-09-10 12:21:49","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":333152,"visible":true,"origin":"","legend":"\u003cp\u003eRiver Boundary and GHB Boundary\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4901377/v1/d1a29731886ee8af12a63eaf.png"},{"id":64222559,"identity":"cb2a9696-85cd-4a85-89fc-070396a0064a","added_by":"auto","created_at":"2024-09-10 12:29:49","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":387852,"visible":true,"origin":"","legend":"\u003cp\u003ePiezometric Surface and Flow Direction Map.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4901377/v1/372ff878525265d1e2203781.png"},{"id":64222237,"identity":"67e70a14-9f8d-45f8-92b0-b197f1e03ca8","added_by":"auto","created_at":"2024-09-10 12:21:49","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":37519,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between time, drawdown and pizometric water level\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4901377/v1/a6afead57a0032f8891376d3.png"},{"id":65066486,"identity":"f9fd121c-a967-4c99-8998-d703a9db4f9b","added_by":"auto","created_at":"2024-09-23 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Introduction","content":"\u003cp\u003eUncontrolled groundwater pumping has caused dramatic changes to our natural landscape. Over- pumping causes severe decline in the water table, resulting in depletion of the streams wetland and land subsidence along rivers, resulting in the destruction of highly productive ecosystems. Irrigation systems also have an indirect impact on the surrounding environment. These indirect effects may not be immediately noticeable as the direct issues. These effects take a longer time to develop and produce longer-lasting changes. In the study area, the main source of water supply for pivotal irrigation projects is the underground reservoir for the extension of agricultural projects away from the Nile River, which makes the specter of depletion loom in far distance due to over-pumping and lack of surface recharge sources (Elkrail, et al \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Moreover, the current situation in Shendi-basin threatens the life of the human communities, the ecosystem and warns of a significant drop in the groundwater level and the depletion of many wells on the edges of the basin, causing human displacement and the loss of many land and agricultural crops. The main objects of this study are to determine the hydrogeological characteristics of the aquifer, calculate the amount of water input, output (water balance) and the storage, as well as estimate the drop in the water level and develop a predictive scenario to avoid depletion risks, Groundwater Flow Model soft ware was used as an appropriate way to do so.\u003c/p\u003e"},{"header":"2. Characteristics of the Study Area","content":"\u003cp\u003eThe area of study comprises the upper part of Shendi –Atbara basin, namely Shendi Formation which is located in the River Nile State, north- central Sudan at about 180Km North of Khartoum. The area lies between latitudes 16º 15`17.7\" - 16º 1`15.6\" N and longitudes 33º 10`57.8\" - 33º 45`33.85\" E. (Fig.1). The study area is a rugged, highly undulated. The hilly terrain is characterized by relatively steep slope toward the east and gentle one to the west toward the River Nile. The fecundity of such areas is due to the effective conjunctive use of surface water from the Nile river and ground water from both the Nile Valley Aquifer (NVA) and Nubian Sandstone Aquifer (NSA) that under lies the region. Historically, farmers in river Nile state relied on the Nile flood pulse to inundate\u0026nbsp;basins which are extensive, flat areas separated from the Nile Valley extended over 20 km from the riverbank in some places. The widespread flooding recharged the aquifers, which were used for supplemental irrigation (Fragaszy \u0026amp; Closas 2016).\u0026nbsp;Groundwater continued to be used alongside the large increase in surface irrigation to ensure the survival of both perennial crops and staples during low-flood years\u0026nbsp;(Bacon 1948).\u003c/p\u003e\n\u003cp\u003eThe River Nile dominates the drainage of the area and represents active locales levels of erosion. North of Khartoum the River Nile flows and cuts centrally through the only upstanding ground formed by Sabaloka Ring Complex. There are number of seasonal water courses that drain to the Nile. Drainage patterns are one of the most important indicators used in the investigation of hydrogeological features. The drainage system is greatly influenced by foliation, faults, and joints of the underlying rocks but on the whole is dendritic drainage pattern. Due to the presence of high and low angle topographic feature beside each other the drainage pattern is in the form of valleys that flow west or northwest towards the River Nile. The most famous one is Wadi Awatieb near to El-Moswarat and Wadi Almocabrab.\u0026nbsp;The study area occupy south of the Central Africa Shear Zone (CASZ). The geology of the southern area is dominated by basement complex rocks. The Basement complex in the study area is affected by tectonic activities, which resulted into widely distributed joints, faults, foliations and folds. The area is characterized by two major rock associations' namely; metamorphic and plutonic igneous rocks, which include acidic character. Metamorphic rocks represent the oldest rock group in the area consist of granitic- gneisses, gneisses, Schists and Quartzite respectively. The following geological units have been distinguished in the study area and are arranged from top to bottom (Delany 1954, Almond 1982, Vail 1974, Kroner, et al 1987, \u0026amp; Sadig, Farwa 1989) (Fig2):\u003c/p\u003e\n\u003cul\u003e\n \u003cli\u003eSuperficial Deposits\u003c/li\u003e\n \u003cli\u003eNubian Sandstone Formation.\u003c/li\u003e\n \u003cli\u003eBasement Complex.\u003c/li\u003e\n\u003c/ul\u003e\n\u003cp\u003e\u0026nbsp;The Nubian sandstone (Cretaceous Sedimentary Rocks) covers 28% of the area of the Sudan and is most important aquifer in the country. It covers together with the basement complex, about78% of the Sudan (Whiteman 1971)\u003c/p\u003e"},{"header":"3. Methodology and Model Construction","content":"\u003cp\u003eThe objectives of this study are to evaluate the groundwater flow system in the study area based on determination of the aquifer characteristics, groundwater flow dynamic, and storage capacity of the aquifers and groundwater balance of the area using groundwater model techniques (Visual MODFLOW code).\u003c/p\u003e \u003cp\u003eThe main input data for model design in the study area that collected and observed from the field work and calculated with relevant methods include: aquifer types, observation wells, pumping wells, recharge sources, aquifer hydraulic properties, initial head and boundary conditions. There are two type of water bearing layers in Shendi basin, upper layer is alluvial aquifer (recent deposits). It is unconfined with high permeability and good water quality. The lower layer is Nubian sand stone aquifer (Cretaceous sediments) is characterized by good hydraulic properties and fresh water quality. The main aquifer materials are unconsolidated sediments layers of Cretaceous deposits. In the lower reach, the aquifer thickness ranges from 50\u0026ndash;125 m with extreme maximum thickness of 135 meters. The depth to groundwater table is about 10 to 37 m below the surface and the average depth to basement is 220 m from the surface.\u003c/p\u003e \u003cp\u003eFor aquifer hydraulic properties, the hydraulic conductivity, specific coefficient, storage coefficient, effective porosity and total porosity were measured with relevant methods for upper and lower aquifer in the model domain. The unconsolidated alluvial aquifers at the upper, varies in thickness from30 to 65 m. and depth to water table is 10\u0026ndash;35 m. The hydraulic conductivity is 1.5\u0026ndash;15 m/d. The specific storage (Ss) is 0.0004, specific coefficient (Sy) is 0.24, effective porosity (ne) is 0.27 and total porosity (nt) is 0.31.\u003c/p\u003e \u003cp\u003eThe Nubian sandstone aquifers at the lower, varies in thickness from 50 to 95 m. The hydraulic conductivity is 1.8\u0026ndash;18 m/d. The storage coefficient (Ss) is 0.00005, specific coefficient (Sy) is 0.25, effective porosity (ne) is 0.27 and total porosity (nt) is 0.31.\u003c/p\u003e \u003cp\u003eBased on the boundary conditions, the bottom of the aquifers and the western side of the model area were considered as no-flow boundaries. The top of the aquifers is considered as the variable head boundary. The southern, eastern and northern sides of the model domain were taken as general head boundary (GHB), whereas, the northwestern part was taken as river boundary (Fig.\u0026nbsp;3). Generally, mathematical model consists of governing equations, boundary conditions and initial conditions. Boundary conditions are mathematical statements specifying the dependent variable (head) or the derivative of dependent variable (flux) at the boundary of the model domain. The boundary conditions express the way the considered domain interacts with its environment. The upper surface of the aquifer represents a flow boundary, where water can enters and leaves the aquifer; through the unconfined layer i.e. water table condition. Therefore, the flow has irregular and random behavior. The top of the aquifer is considered as the variable head boundary, where flow may enter the model as a recharge from the River Nile seasonal stream and direct precipitations. The southern, eastern and northern sides of the model were taken as General Head Boundary (GHB) of 390, 380 and 388 m, above sea level (m, a.s.l) respectively for upper aquifer, whereas GHB of 328, 322 and 321(m, a. s. l) were assigned to the southern, eastern and northern sides of lower aquifer respectively and Boundary conductance is 6500m2/d. The western side of the model area was assigned as river boundary, along the River Nile course.\u003c/p\u003e \u003cp\u003eThe hydraulic conductivity of 1.5\u0026ndash;15, the specific coefficient of 0.24, storage coefficient of 0.0004, effective porosity of 0.27 and total porosity of 0.31 were assigned to the upper aquifer. On the other hand, hydraulic conductivity of 1.8\u0026ndash;18 m\\d, the specific storage of 0.25, storage coefficient of 0.00005, effective porosity of 0.27 and total porosity of 0.31were assigned to the lower aquifer for model simulation. The measured heads in the observation wells were used as initial head distribution for the model simulation. The bo5ttom of the aquifer and the western side of the model area were considered as no-flow boundaries. The top of the aquifer is considered as the variable head boundary, where flow may enter the model as a recharge from the River Nile seasonal stream and direct precipitations. The southern, eastern and northern sides of the model were taken as General Head Boundary (GHB) of 390, 380 and 375 m, above sea level (m, a.s.l) respectively for upper aquifer, whereas GHB of 388, 370 and 365 (m, a.s.l) were assigned to the southern, eastern and northern sides of lower aquifer respectively. The western side of the model area was assigned as river boundary, along the River Nile course.\u003c/p\u003e"},{"header":"4. Results and Discussion","content":"\u003cp\u003eFrom the piezometric surface map Fig.\u0026nbsp;(4), the general flow direction is from the west to the east and northeast, confirming the natural aquifer recharge from the River Nile which is one of the model credibility. Semi-cone of depression was observed at the center of the area due to heavy pumping for agricultural activities (pivotal irrigation) at these areas (Elkrail, et al \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). The zone budget was calculated for steady state model simulation for the whole model domain (Table). The volume of water in cubic meter per day (m3/d) and its percentage was calculated for each component of the hydrologic budget. Recharge is the most important hydrologic component of inflow to the aquifer, which is able to offset the groundwater extraction from the aquifer. The total volume of the aquifer inflow is (1305381m\u003csup\u003e3\u003c/sup\u003e/day), while the total volume of the aquifer outflow is 1304902m\u003csup\u003e3\u003c/sup\u003e/day (Table\u0026nbsp;5.1). Groundwater pumping volume through production wells in the entire area computed by the model represents 54% of the total outflow from the aquifer. The subsurface inflow through the GHB represents 14.4% from the total inflow. The river recharge to the aquifer as subsurface inflow represents 29.7% of the total inflow. The recharge water volume from direct precipitation represents 55.9% of the total inflow. The subsurface outflow through the GHB from the aquifer represents 40.5% from the total outflow. Finally, the discrepancy between inflow and outflow amount to 478 m3/day as daily water reserve.\u003c/p\u003e \u003cp\u003eNumbers of scenarios were performed to study the impact of well discharge increasing rates to drawdown, subsurface Inflow, Outflow through the GHBs at the model domain of Shendi sub- Basin (Table\u0026nbsp;4.). The Projected Growth Scenario simulates increased groundwater discharge to meet water demands due to the rapid population and agricultural activities growth. The incremental percentage rate of wells discharge in study area by 20%, 40%, 60%, 80%, and 100% from the original pumping rate were simulated Table\u0026nbsp;(5.2). Groundwater subsurface flow (inflow \u0026amp; outflow) was quantified by MODFLOW simulation as GHB condition. The resultant increasing drawdown and subsequent increasing subsurface inflow and decreasing subsurface out flow through GHB were reported. The results of simulation indicate that increased wells\u0026rsquo; pumping to meet future demand will likely result in more dramatic declines in groundwater levels with maximum drawdown of 13.39 m (Table\u0026nbsp;2) and relatively increasing subsurface inflow and decreasing subsurface out flow.\u003c/p\u003e \u003cp\u003eThe data of the wells drilled in the period before the establishment of pivot irrigation projects were studied and compared with the neighboring wells drilled at a later time for pivot irrigation until the year 2020, showing a significant drop in the ground water level, which exposes many wells to depletion. The water level measured at two adjacent wells before and after the pivotal irrigation period, show considerable drop in the piezometric surface in the area., Clear drop of water level was monitored ranging from 3 meters near the Nile to 10 meters at the middle of the area ( Maaqil area), and the decline increases east up to 15 meters in the far east (Bir Al-Jud) at 30 km from the Nile. The half_ life of the well is shortened and exposed to depletion quickly, as in Elgemma agricultural project Table\u0026nbsp;(3).\u003c/p\u003e \u003cp\u003eIn a number of agricultural projects in the eastern direction (28 km far to the River Nile (Elgemma Agriculture Project) outskirts of the basin monitored the depletion of a number of wells as in the agricultural summit projects, in this case annually one well at least faced the threat of depletion, static water level was withdrawal with the value exceed 9\u0026ndash;12 m in some locations Table\u0026nbsp;(3). Figure\u0026nbsp;(5) shows dramatic change in piezometric level in different localities with minor change in drawdown (dd). In the central part of the basin and towards the Nile River, the depth to water level decreases up to the river bank. Before a pivotal irrigation activities, the depth to water level ranged from 11m to 27m far east of the River Nile with an average of 18.3 m, While the water levels reached the range from 12 to 38 m with an average of 27.5 after pivotal irrigation activities, coinciding with deterioration in the amount of water replenishment for the aquifers in the basin. One of the most significant causes of ecological damage in the study area is the reduction of groundwater storage which led to wells depletion in agricultural projects which reflected on human activity and vegetation in the region. Moreover, the reduction of groundwater storage due to mismanagement of pivotal irrigation, results in insufficient drinking, industrial, and municipal water supplies, which significantly change the ecosystem. To reduce the impact of the pivotal irrigation activities good relevant management scenarios should be conducted in the study area. The results of simulation indicate that increased wells\u0026rsquo; pumping to meet future demand will likely result in even more dramatic declines in groundwater levels.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eThe authors appreciate the outstanding logistical and technical support provided by Ministry of Water Resources and Irrigation\u0026nbsp;\u003c/em\u003e\u003cem\u003eT\u003c/em\u003e\u003cem\u003ehey also acknowledge the El Neelain University\u003c/em\u003e\u003cem\u003e\u0026nbsp;for vital support.\u003c/em\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eElkrail, A.B., Amin Dafalla and Mohamed Adlan (2019): Numerical Simulation of Groundwater Flow in Shendi Sub-Basin, Sudan.\u003c/li\u003e\n \u003cli\u003eFragaszy and Closas (2016): Irrigation expansion in Northern State, Sudan, pp.158\u003c/li\u003e\n \u003cli\u003eBacon, G. (1948): Crops of the Sudan. In Tothill, J. (Ed), Agriculture in the Sudan: Being a handbook of agriculture as practiced in the Anglo-Egyptian Sudan, pp. 302-400. Oxford: Oxford University Press.\u003c/li\u003e\n \u003cli\u003eDelany, F. M., (1954):Recent contribu- tions to the geology of the Sudan. Ninteenth int. Geol. Congr. Algiers, 20: 11-18.\u003c/li\u003e\n \u003cli\u003eAlmond, D. C., (1982): New ideas on the geological history of the Basement Complex of NE Sudan. Sudan Note and Rec. 59: 106136.\u003c/li\u003e\n \u003cli\u003eVail, J.R., (1974):. Distribution of the Nubian Sandstone Formation in Sudan and vicinity. AAPG Bulletin, 58, 10251036.\u003c/li\u003e\n \u003cli\u003eKr\u0026ouml;ner, A., Greiling, R., Reischmann, T., Hussein, I. M., Stern, R. J., Durr, S. and Zimmer, M., (1987a): Pan-African crustal evolution in the segment in the northern Africa. In: Kro\u0026uml;ner, A. (Ed.), Proterozoic Lithosphere Evolution. International Lithosphere Program Publication 130. American Geophysical Union Geodynamics Series, Washington, DC. 17: 235\u0026ndash;257.\u003c/li\u003e\n \u003cli\u003eSadig and Farwa (1989).Delineat the Umm Marahik basin and its bounding faulted contact in Sabaloka area. They confirmed the general condition that the gravity method is a useful tool in the exploration of groundwater.\u003c/li\u003e\n \u003cli\u003e\u003cstrong\u003e\u0026nbsp;(\u003c/strong\u003e9) Whiteman, A. J. (1971): The geology of the Sudan Republic. Clarendon Press, Oxford, 299 pp.\u003c/li\u003e\n \u003cli\u003eElkrail, A. , Awad, T. Yousif, Y. (2014). Numerical simulation of groundwater flow in southeast of el Damer town, river Nile state, Sudan, American Journal of Earth Sciences 2014; 1(1): 21-24.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 to 3 are available in the Supplementary Files section\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Pivotal irrigation system, conceptual model, MODFLOW, aquifer, hydraulic parameters","lastPublishedDoi":"10.21203/rs.3.rs-4901377/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4901377/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe hydrogeological system, in the study area, consists of two aquifers, namely; shallow and deep aquifer. These aquifers show a wide range of variable hydraulic parameters, due to rapid lateral and vertical changes of Facies. The deep aquifer is characterized by higher hydraulic parameters, large volume and, consequently, higher productivity compared to the shallow aquifer. These valuable resources are threatened by the impacts of accelerated overexploitation and flood irrigation practices, and may be severely over drafted or may be subjected to continuous decaling of water level and water quality degradation if not managed properly. Previous geological and hydrogeological studies have established that significant overexploitation influence the flow characteristics and water quality, which influence the possibility of using groundwater as a main water resource. The conceptual hydrogeological model was developed using Visual MODFLOW software to assess the impact of pivotal irrigation on groundwater potentiality in shendi sub-basin. Numbers of scenarios were performed to study the impact of well discharge increasing rates to drawdown, subsurface Inflow, Outflow through the general head boundaries (GHBs) at the model domain of Shendi sub- Basin. The results of simulation indicated that increasing wells’ pumping rate to meet future demand will likely result in more dramatic declines in groundwater level with maximum drawdown of\u003cstrong\u003e \u003c/strong\u003e13.39 m. The piezometric surface measured at two adjacent wells before and after pivotal irrigation period, showed a drop of 10m in the groundwater level. Mearements of ground water levels after the pivotal irrigation period show a clear decline ranging from 3 m near the Nile to 10 m at the middle of the area (Maaqil area), and increases eastwards up to 15 m (Bir Al-Jud, 30 Km from east of the river Nile. Most of the wells are exposed to depletion during the pivotal irrigation periods as in Elgemma agricultural project. The most significant impacts of pivotal irrigation in the study area are the ecological damage such as severe reduction in groundwater storage which led to the depletion of wells in agricultural projects which affected the human and vegetation activities in the region. Additionally, it results in insufficient drinking, industrial, and municipal water supplies, which significantly change the ecosystem.\u003c/p\u003e","manuscriptTitle":"Assessment of Excess Abstraction Impacts by Pivot Irrigation on Ground Water Quantity in Shendi Sub-basin, Sudan","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-09-10 12:21:44","doi":"10.21203/rs.3.rs-4901377/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"28e6f172-5f6e-48f2-bb27-c303005110fd","owner":[],"postedDate":"September 10th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-09-23T08:54:28+00:00","versionOfRecord":[],"versionCreatedAt":"2024-09-10 12:21:44","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4901377","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4901377","identity":"rs-4901377","version":["v1"]},"buildId":"WrCJVZZCHTDjtuVLN7oU0","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}