Evaluate the Effects of Watershed Characteristics on Stream Flow, the Case of Blue Nile River Basin, Beshilo Watershed, Ethiopia.
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Date
2018-10
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Addis Ababa University
Abstract
Land degradation is a series problem in Ethiopia highlands, particularly in Blue Nile River Basin
reflected in the form of soil erosion and soil fertility decline from time to time. Beshilo watershed is
one of the major Blue Nile River Basin tributary, which covers 5,700 km2. The effect of watershed
characteristics on Stream flow of Beshilo watershed were evaluated by distributed physically based
hydrological model known as soil and water assessment tool (SWAT) model. The model was used
for detail evaluation of the watershed characteristics on stream flow and the effects of physical
watershed characteristics were analyzed and character which have higher effect on stream flow were
identified and also identify model remedial measure for most stream flow generation in the
watershed. The model was calibrated and validated by transferred flow data from gauged upper
reaches of Gummara watershed to ungauged Beshilo watershed. The model was calibrated for the
period from 1999-2008 and validated for the period from 2009-2014. The performance of the model
was evaluated on the basis of performance rating criteria, coefficient of determination, and Nash &
Sutcliff efficiency on monthly based value, the coefficient of determination (R2) and Nash- Sutcliffe
coefficient was 0.77 and 0.80 for calibration period, 0.83 and 0.84 for validation period. The overall
performance of the models gives good result and the effect of watershed characteristics on stream
flow were evaluated and tested by created different scenarios. The land use land cover change
scenario, the climate characteristics and the slope change scenario are developed, from the land use
land cover change analysis, it was found that has been a substantial decline of forest land, shrub
land, grass land and expansion of agricultural land. The mean annual stream flow at 2004 LULC
were increase by 7.4 % compared from 1996 LULC and increased by 6.8 % compare from 2013
LULC. Whereas compared the two recent LULC 2004 and LULC2013, at 2013 LULC the stream
flow decrease by 2.3 %, this result show that LULUC change was affect the stream flow in the
watershed. And the other scenario were developed by increasing the average tributary slope by 5%
rate and decrease by 5% rate, the annual stream flow averagely increased by 2.1% and decreased by
1.8 % respectively. Whereas the climate effect was observed by changing the climate data with 10
year interval, the model output clearly demonstrate physical watershed characteristics affect the
stream flow, the land use land cover change was highly affects the stream flow in Beshilo watershed.
So, to reduce the stream flow in the study area land use land cover management is important.
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Keywords
Watershed, Stream Flow, Blue Nile River Basin, Effects of Watershed, Beshilo Watershed