Browsing by Author "Birhanu, Birhanu Zemadim"

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    Application of a GIS based swat model in simulating the available water resources in a Pangani river basin sub catchment: a case study of catchment
    (University of Dar es Salaam, 2005) Birhanu, Birhanu Zemadim
    In this study a G1S based, distributed hydrologic model SWAT (Soil and Water Assessment Tool) was used for modeling 1DD1 catchment in the Pangani river basin. Previous researches conducted in assessing the available water resources in Pangani river basin used a lumped and semi distributed approach in modeling the catchment. In this study a physics based, complex hydrologic model was developed by considering the major water abstractions for irrigation to estimate the available water resources. Spatial and time series data used in the study were obtained from the Water Resources Engineering Department (WRED) and various government offices, and these data were prepared in the required format for the model input using various programs. The Rainfall-Runoff modeling was conducted based on a spatial calibration technique for the global water balance simulation and temporal calibration. SWAT model was initially tested for small sub catchment and produced a Nash and Sutcliff efficiency criteria (R2) of 82.4% and 59.4% during calibration and validation, and its distributed capacity was reflected from the modeling scenario of subdividing the catchment in to six sub basins and incorporating abstraction and spring data which resulted an R2 of 75.9% and 45.9% during calibration and validation. The estimated average annual water yield from the districts that lie with in 1DD1 catchment are 127.381mm and 303.697mm from surface and ground water sources respectively, which shows that most of the water yield in the catchment is from the ground water sources. The conflicts in Pangani river basin in the use of water would be avoided by sharing the available water resources depending on the demand and utilizing the abundant ground water resource in the region.
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    Development and Application of Distributed Hydrological Model for the Central and Southern Catchments in the Eastern are Mountains of Tanzania
    (University of Dar es Salaam, 2008) Birhanu, Birhanu Zemadim
    Eastern are mountains (EAMs) catchments have experienced significant flow reductions since late 1970s, and due to varied physiography and hydro-climatic conditions the available hydrological networks are not well enough for sound assessment of water resources. Various sources attributed the flow reductions to land use and land cover changes in the catchment over the years. In this study the effects of catchment cover changes were studied together with the hydrological behavior of the of the EAMs catchments. Distributed and physics based hydrological model and empirical and conceptual models were developed using results of remote sensing GIS technology and hydro- metrological data. The results of the study showed no significant impact on the simulated flow a due to the effect of land cover changes. For example, using a scenario land cover changes in some 8.34% of the catchment area, a change in annual flow to the extent of only 4.7% was observed which nearly 84% was attributed to ground water flow alone. The research also indicated that parameter reductions and use of catchment characteristics in hydrological model development improved the efficiency of hydrologic variables predictions. This research further demonstrated that streamflow reductions in the studied area were attributed to valley bottom cultivation through current abstractions at the valleys are not documented but indicative of creating soil moisture deficit with high loss of water by evaporation. The developed hydrological models are suitable tools for environmental modeling and wider applications are recommended for comprehensive understanding of the hydrological processes of tropical catchments.