University of Twente Student Theses


Water Balance Modelling for Reservoir Planning in Ribb Catchment, Ethiopia

Selman, Mecca (2009) Water Balance Modelling for Reservoir Planning in Ribb Catchment, Ethiopia.

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Abstract:The Ribb Reservoir is located East of Lake Tana in Amhara regional state 23km from Debre Tabor town in the North West part of Ethiopia. The geographical location of the reservoir at outlet is 12° 02’ 30”N 37° 59’ 45”E. The catchment including the reservoir covers a total area of 668km2. Ribb reservoir is located in semi- arid region and suffers from water scarcity and due to this reason proper management for optimum use of the available fresh water resources is very crucial. The objective of this work is to assess the available water resources as it is the most important step towards proper management. In this study, the components of water balance have therefore been assessed using a reservoir water balance method for the period 1997 to 2006. For the case of runoff assessment per land cover unit, the catchment area has been classified into five land cover units (bareland, crops, forest, grassland and water) using Landsat images. The mean annual runoff from the catchment was estimated of 215 Mm3. Runoff and rainfall are the two components constituting the total inflow to the reservoir. Irrigation water demand, evaporation and environmental flow are the outflow components of the reservoir. Evaporation for open water is determined by Penman combination equation and precipitation is interpolated by inverse distance and Thiessen polygon weighting. Change in storage was calculated by determining all components of the reservoir. Catchment extraction was established from ASTER image elevation data and the catchment is divided in to three subbasins. The HBV-96 model was applied to simulate the runoff from Ribb River using daily hydrometeorological data. The Nash-Sutcliff efficiency between observed and simulated of calibration and validation of the model shows that R2 = 0.8 for calibration and R2 = 0.81 for validation. The storage capacity of the reservoir was estimated using ILWIS software through, trapezoidal and prismodal methods. Irrigation water demand was estimated by using CROPWAT for windows and environmental flow was determined by long-term monthly average flow of the river.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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