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Modeling Sediment Yield, Transport and Deposition In The Data Scarce Region of Ethiopian Rift Valley Lake Basin

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dc.contributor.advisor Bayou, Chane (PhD)
dc.contributor.advisor Assefa, Mekonnen (Prof.)
dc.contributor.author Alemu, Osore
dc.date.accessioned 2019-06-24T04:22:21Z
dc.date.available 2019-06-24T04:22:21Z
dc.date.issued 2018-12
dc.identifier.uri http://etd.aau.edu.et/handle/123456789/18548
dc.description.abstract Knowledge of sediment yield, transport and deposition processes taking place in a river basin is necessary to find suitable mitigation measures for reservoir sedimentation and to estimate lifespans of reservoirs. This research is undertaken to analyze the sediment yield of catchments, transport capacity of streams and sediment deposition rates and patterns in Lake Ziway Basin, Rift Valley Lakes Basin of Ethiopia; and to develop a sediment yield predication model by considering the soil, geomorphologic and hydrologic parameters of the basin. Sediment yield of Lake Ziway Basin and sediment flux of the streams discharging into the Ziway Lake is modeled; and the sediment yield is estimated to be 2.081 Mt/year. Quantity of sediment that deposits in the floodplains, leaves the Lake through Bulbula River and that deposits in Ziway lake is estimated to be 0.178 Mt/year, 0.0413 Mt/year and 2.039 Mt/year, respectively. Based on the established sediment budget, Lake Ziway will lose its volume by 0.106% annually and its life-span is predicted to be 947 years. This result is validated by multi-frequency reservoir survey techniques using the lake bathymetry survey data obtained in 2005 and 2017. In the period of 12 years extending between the bathymetric surveys, 17.75 MCM (4.2cm average thickness) of sediment is deposited in the lake. Assuming a constant deposition rate in the period, the reservoir sedimentation rate is 1.81 Mt/year. This results in about 0.093% annual storage capacity reduction and 520 years expected half-life of the lake. By using the SWAT model, soil erosion risk and hot spot erosion area of the basin is assessed. Soil conservation scenarios that reduce the slope length of the watershed by 50%, can decrease the sediment yield of the basin by 55%. As the soil erosion is the product of erosivity and erodibility, an alternative soil erodibility estimation factor (KET) is derived from the soil data of the Ethiopian Rift Valley Lakes Basin (ERVLB) and has been evaluated for its applicability for soils found across Ethiopia. Statistical values of the analysis indicate that, the performance of KET is excellent for soils of ERVLB and acceptable within ±5% relative error for 35.7% of the soils across the country. Thus, KET values can be applied for soils found across Ethiopia with relative error and standard deviation of -9.88% and 6.4, respectively. An empirical model is developed to estimate the sediment concentration of rivers in Ziway Lake Basin based on hydro-geomorphology and stream flow characteristics and tested for its applicability. Validation of the model showed an acceptable performance. To conclude, this study provides an appropriate method to estimate the soil erodibility rate and sediment flow rate of the basin. Applying the method, high sediment risk area of the basin is identified. The method will be useful for concerned organizations to mitigate erosion rate at hot spots and at any part of the basin as necessary. The study has developed, the lake stagevolume- area relation which can be used for future water resource assessment studies. en_US
dc.language.iso en_US en_US
dc.publisher Addis Ababa University en_US
dc.subject Sediment Yield en_US
dc.subject Ethiopian Rift Valley Lake Basin en_US
dc.subject Transport en_US
dc.subject Deposition en_US
dc.subject SWAT model en_US
dc.subject soil erosion en_US
dc.title Modeling Sediment Yield, Transport and Deposition In The Data Scarce Region of Ethiopian Rift Valley Lake Basin en_US
dc.type Dissertation en_US

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