HYDROLOGICAL RESPONSE TO LAND USE LAND COVER DYNAMICS AND SUB WATERSHED PRIORITIZATION FOR LAND AND WATER MANAGEMENT (Case study of Tekeze dam watershed, Northern Ethiopia)

Abstract

Land use change is a very important issue considering global dynamics and their response on hydrologic characteristics and soil and water management of an area. Significant land use changes have observed in Tekeze dam watershed using 1986 and 2008 LULCs as a reference time. The main objective of this study was to estimate the potential impacts the LULC dynamics on hydrological response and prioritization of sub-watersheds according their sediment potential. This was done by integrating SWAT model with GIS. The simulation and sensitivity analysis for each land use was done by dividing the watershed in to 47 sub-watersheds and assigning HRUs based on multiple HRU definition. Both automated and manual calibrations were done using time series data 1978-1982 for 1986 LULC and 1996-2002 for 2008 LULC. The model was validated using an independent time series data of 1983-1985 for 1986 LULC and 2003-2006 for 2008 LULC. After performance of the model was evaluated and become in its recommended limit using statistical performance indicators, impact of LULC dynamics on stream flow and sediment yield was evaluated using three scenarios (climate of 2000s & 2008 LULC, climate of 2000s & 1986 LULC and climate of 1980s & 1986 LULC) and sub watersheds were prioritized using the first scenario. Significant change in response of the catchment stream flow and sediment yield was obtained due to LULC dynamics. Accordingly, the mean annual stream flow increased by 6.02% (129.20 to 137.74 m 3 /s) and the impact on sediment yield amounts to an increase of 17.39% (12.54 to 15.18 ton/ha/yr). The first 13 sub-watersheds, whose annual sediment yield limit ranges above the tolerable limit (18 ton/ha/year), were prioritized according their sediment for watershed management efforts. The maximum sediment outflow of these 13 sub watersheds ranges from18.49 to 32.57 ton/ha/year and are characterized dominantly by cultivated land, shrub land, bare land & grass land with average land slope ranging from 7.9 to15.2% and with dominant soil type of Eutric cambisols. Therefore these results can help to formulate and implement effective, appropriate and sustainable watershed management which in turn can help in sustaining the reservoir storage capacity of the dam.