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Accueil du site → Master → Pays Bas → 2014 → Groundwater modeling and optimization of irrigation water use efficiency to sustain irrigation in Kobo Valley, Ethiopia

UNESCO-IHE Institute for Water Education, Delft (2014)

Groundwater modeling and optimization of irrigation water use efficiency to sustain irrigation in Kobo Valley, Ethiopia

Adane, G.W.

Titre : Groundwater modeling and optimization of irrigation water use efficiency to sustain irrigation in Kobo Valley, Ethiopia

Auteur : Adane, G.W.

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

Grade : Master of Science (MS) 2014

Agriculture, Industry and domestic activities use enormous of water which results in the over-pumpingand leading to continuous decline of groundwater level.Farmers often fail to satisfy the required soil moisture conditions for growing crops due to erratic low rainfall distribution. Poor on-farm water management practices resulted in excessive use and this leads to high energy cost. This study mainly focuses on groundwater modelling of kobo valley so as to predict the current and future groundwater level under different hydrologic and pumping scenarios. Aqua crop model was also used as a tool for assessing cropand water productivity under irrigated agriculture - the main production system in Kobo valley, the main study area of this research, located in Northern Ethiopia is enclosed by high mountain ranges on the edge of Afar Rift system and measures about 1200km2area. It has two main sub-basins, Hormat-Golina and WajaGolesha that are characterized by high abundant resources with respect to groundwater, fertile land and livestock potential. The groundwater flow system in unconsolidated deposit of Kobo valley was modelled using MODFLOW (McDonald and Harbaugh, 1988). The model was run for steady-state conditions in unconfined and confined aquifer. The grid cell size of the model was taken 300 x 400m and contains two layers. Model area and the layer top elevation were delineated bythe ASTER DEM processing and use of topographic maps. The hydraulic conductivity values were determined from pumping test data analysis and literaturereview for the alluvial sediment aquifer and the fractured volcanic aquifer respectively. Recharge wasestimated from water balance and Darcy’s approach method and has a value of 95MCM and 83 MCM respectively. The model was calibrated using observed hydraulic heads from 35 wells from Hormat-Golinasub-basin using trial and error method and resultedin a Root Mean Square Error (RMSE) value of about 7m, which is considered to be good and an indicatorof reliable model results. The model simulated water budget showed that the valley receives a total recharge of 118MCM /year. The steady state model with pumping scenarios :- current scenario (11 wells areoperated simultaneously), scenario-one (35 wells are operated simultaneously) & scenario-two (70 wells are operated simultaneously) indicated respective groundwater abstraction of 5192 m3d-1, 27878 m3d-1and 55825 m3d-1 .This resulted in an average groundwater level decline (at the pumping well) of about 7m, 14m and 32m respectively. A maximum of 35 wells simultaneous operation is recommended as this will maintain a 20% stabilized drawdown, which results in a balance between abstraction and recharge. The current irrigation system is operating at an efficiency of 55% as the actual amount of water applied is about 730 mm while the net requirement obtained from Aqua Crop is 404 mm. Under groundwater based irrigation, the efficiency could be improved to 80%through the use of piped conveyance canals and good field water distribution that reduces runoff and deep percolation losses. Under the current actual harvest by the farmers of 1.8 ton/ha, and assuming only the fuel cost, the difference in net income between operating at 55% and 80% efficiency is 109 Euros/ha. If, however, the yield could be improved to 4.7 ton/ha (this yield is obtained by farmers in others regions of Ethiopia), the difference in net income is nearly 1000 Euros/ha.

Sujets  : groundwater modelling irrigation water optimization Ethiopia


Page publiée le 13 février 2020