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UNESCO-IHE Institute for Water Education, Delft (2016)

Optimum water allocation in the Gash River basin : Sudan

Berhe, Y.T.

Titre : Optimum water allocation in the Gash River basin : Sudan

Auteur : Berhe, Y.T.

Université de soutenance : UNESCO-IHE Institute for Water Education, Delft

Grade : Master of Science (MS) 2016

Résumé
There is a growing competition over scarce water resource among different stakeholders to satisfy their basic water requirements. In this view, optimal water allocation to maximize benefits becomes a necessity. Such a case is exemplified by Kassala region, Sudan, where most of the projects and studies focus on exploiting the Gash River without integrating all the users. The socioeconomic activity of the region solely depends on seasonal Gash River, which flows between July and October with an average annual discharge of 680 million m3/year. Analyzing the gap, this research is developed with an objective of allocating the stochastic Gash River to optimally satisfy all stockholders under the current and future (2050) demands. A River Basin Simulation Model (RIBASIM) has been used to allocate the Gash River to different stakeholders, based on the priority of the society and forecasted demand of each user in 2016 and 2050. The main users of Gash water are Gash Agricultural scheme (GAS), public water supply (PWS), irrigation of vegetables and fruits, Gash Die Inland delta ecosystem and natural vegetation. The stochastic nature of the flood is described by categorizing the flood year into dry, normal and wet hydrological years, with an average cumulative annual flow of 375 million m3 , 630 million m3 and 960 million m3 in dry, normal and wet hydrologic years respectively. With such a variation of flood in each hydrological year the supply to each stakeholder varies significantly. Simulation in each hydrologic year is done for the current (2016) and future (2050) demands. The simulated result showed that it is impossible to satisfy the total current (2016) and future (2050) demand of stakeholders in all hydrological years. For the predicted water consumption in 2050, the model simulated a total shortage of 1,378 million m3 per year and 380 million m3 per year ground water depletion in dry hydrologic year. To reduce this shortage three intervention scenarios are developed, simulated and evaluated by multi-criteria analysis for maximal compromised societal benefits using economic efficiency, social equity, and environmental sustainability criteria. Based on the analysis, the first two scenarios reduced the total shortage to 809 and 893 million m3 per year. This is mainly attributed by reducing Mesquite vegetation by 50%, improving the irrigation efficiency of GAS to 60% in the first intervention scenario and reducing Mesquite vegetation and the ecosystem area by 50% in the second intervention scenario. While the third scenario has produced the least shortage of 583 million m3 per year and provided the highest societal benefit. The third scenario is basically a reduction of Mesquite trees by 75%. The research concluded that decision makers of Kassala region should allocate the flood based on the priority of the society and predicted amount of flood by integrating all users. Moreover, the research recommends the decision makers to adopt the third scenario as the tree not only consumes a lot of water for real production but compete with natural vegetation and crops which are very important for millions of people and livestock in the Gash Delta.

Mots Clés  : water allocation ; river basin management ; simulation models ; water resources management ; Gash River ; Sudan

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