Runoff and Sediment Yield Simulation in the Weyib Watershed, Genale-dawa Basin, Ethiopia
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Date
2021-03
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Addis Ababa University
Abstract
The SWAT model was applied to simulate the runoff and sediment yield from the Weyib
watershed. This watershed has an area of 24369.6 km2
and located in South-Eastern part of
Ethiopia, sharing two regional states, Oromia and Somali. The objective of this study was to
estimate soil loss rate in the study watershed and to identify appropriate intervention measures to
control erosion. In spite of the serious erosion problems in the study watershed, so far only few
studies related to erosion are available. Consequently, this study was conducted with the aim of
contributing to the exiting insufficient quantitative information on soil erosion problems. Due to
the absence of measurements for some of the stations, about 25 years meteorological data and 21
years flow and sediment data generated by regional equations were used for the analysis. On the
other hand, the SUFI2 program in the SWAT-CUP was applied for model calibration and
validation using time series data from 1992-2012. The model prediction efficiency was evaluated
using statistical model performance indicators like, coefficient of determination (R2
) and NashSutcliffe model Efficiency (ENS) and the result showed that both surface runoff and sediment
yield were estimated satisfactorily, with an R
2
and NSE values of greater than 0.67 each, both for
calibration (1994–2004) and validation (2005-2012) periods. The model prediction for the average
annual precipitation and run-off was 1029.2mm and 311.30mm, respectively; whereas, the model
prediction for the average annual total sediment load was 1.23t/ha. The annual soil loss estimated
by the model for the Weyib watershed during the simulation period 1992-2012 ranges from 12.49
ha−1
year−1
to 88.36 ha−1
year−1
, with an average value of 37.33 tons ha−1
year−1
. In this study, Subwatershed 6, 7, 8, 10 and 12 were found to have the maximum annual sediment load, having an
annual sediment load of greater than 20 tons/ha/yr, sub-watershed 8 being the most erodible area,
and as these sub-watersheds were most sensitive to erosion, they were labeled as erosion hotspot
areas. Different intervention scenarios were developed for erosion control and proper management
of the watershed. Simulation results for these scenarios reflected that, 35-78% sediment yield
reduction could be achieved by implementing filter strips, stone bunds, contour farming, fanya
juu, bench terraces and from the combination of these. On the other hand, conversion of
agricultural lands to forest areas reflected a 10-45% sediment yield reduction.
Description
Keywords
SWAT Sediment yield, Runoff, Soil Erosion, Weyib watershed