ABSTRACT
Land-use change has been a
factor that alters the hydrologic response of the watersheds leading to
influencing on sediment yield changes. This study is mainly focusing on the
assessment of the impacts of the land-use changes on sediment load and lake
depth reduction on Lake Ziway, Ethiopia using an integrated approach of Remote
Sensing (RS), GIS and SWAT model. ERDAS IMAGINE 14 model was used to generate
land-use maps from Landsat TM, ETM+, and Ls8 acquired, in 1988, 2002 and 2015
as representative for the periods of (1988-1998), (1998-2008) and (2008-2018), respectively. The maximum likelihood
algorithm of supervised classification applied to classify the basin land-use into seven land-use classes. The
SWAT hydrological model with ArcGIS interface setup for the basin to
evaluate the flow and sediment load with calibration and validation performance
of the model range R2 (0.71 - 0.89) and NSE (0.57 - 0.87). As a result, the total average annual
sediment yield from the sub-basins estimated as 3.59 t/ha/yr, 4.36 t/ha/yr, and 4.89 t/ha/yr for three consecutive
decadal periods 1988-1998, 1998-2008, and 2008-2018 respectively. The increasing trend of sediment yield in the Lake
Ziway watershed through one period to another justified as due to land-use.
Similarly, the net sediment volume deposited in the lake also showed
incremental trained with the land-use changes
as 1.5 mcm/yr, 1.81 mcm/yr, and 2.033 mcm/yr for the period of
1988-1998, 1999-2008, and 2009-2018, respectively. The depth and water holding
capacity of the lake reduced by 4.3 m and 25.76 mcm, respectively, from the depth and capacity
recorded on the 2006 bathymetric survey,
which was the effect of deposited sediment over the last 12 years.