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UNESCO-IHE Institute for Water Education, Delft (2007)

Analysis of sediment transport in the diversion headwork of Shilanat irrigation scheme

Wubneh, A.M.

Titre : Analysis of sediment transport in the diversion headwork of Shilanat irrigation scheme

Auteur : Wubneh, A.M.

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

Grade : Master of Science (MS) 2007

Résumé
Sediment transport in river flow has often presented a major problem in irrigation systems,as the main canals of irrigation projects often suffer from excessive sedimentation whichenters the system via the headwork. This problem results from the fact that the sedimenttransport in river diversion is often not well assessed. The problem is acute in Arid andSemi-Arid areas where rain water harvesting techniques are a priority option for irrigationwater.This study focused on the diversion headwork of Shilanat irrigation scheme where themethod of water harvesting is through diversion of runoff water during the flood seasonfrom Zamra River, which is ephemeral. The Shilanat irrigation system, as in many othersystems, has a sedimentation problem at the intake structure of the river diversion work andreservoirs. Therefore, this study tries to address the following issues : possibilities ofminimizing sedimentation in the diversion headwork ; evaluate the performance of thediversion weir ; and estimate the resulting reservoir life time of the storage micro dams.The study used primary data that included : sediment samples at different locations,topographic survey of the diversion weir using total station ; topographic survey of thereservoir using a floating boat ; measurement of the dimensions of diversion headworkcomponents ; and information on the operation system and general phenomenon in the studyarea. The study also used the following secondary data : land use of the catchment ; rainfalldata ; design drawings ; and reports.The study was analysed using Delft3D, a multi dimensional hydrodynamic modelincluding morphology. The two-dimensional depth average model was used to model thesedimentation phenomenon in the river diversion weir. An attempt was made tounderstand the sediment transport phenomenon after intensive calibration of the modeland conducting different scenarios. The scenarios included the understanding ofsediment particle size distribution in the diversion area and comparing this with the fieldmeasured data, flushing system under different sluice gate dimensions, and relative locationof intake position with respect to the weir (dam). Moreover, the sediment deposition processin the micro dam was analysed using GIS (Geographic Information System) and theresulted life time expectancy of the reservoir was about 53 years which is exceptional in theregion. An evaluation was also done on the overall performance of the diversion weir fromboth technical and managerial view.This study analysed the sedimentation phenomenon and concludes that even the bestdesign does not work without good operation and management of the diversionheadwork. To reduce this problem, the study proposes an alternative layout and designoption with consideration of big boulders and huge sedimentation problem, particularlyto severe sediment prone areas. The study also recommends that the problem can bemanaged if each beneficiary (farmer) can contribute to dredge 2 m3 of sediment per yearbefore the beginning of the rainy season

Sujets  : sediment transport irrigation schemes hydrodynamic model water harvesting reservoirs rivers

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Page publiée le 29 février 2020