Abstract:
Runoff and sediment yield modeling was important in the Meki river watershed. Runoff and
sediment yield modeling and the evaluation of best management practices is important to
alleviate soil erosion and reservoir sedimentation. The general objective of this study was
to model the runoff and sediment yield and to assess best management options to control
soil erosion and sedimentation problems of the Meki River Watershed. The main materials
and data used for input data preparation, analysis were, Arc GIS, Arc SWAT, SWAT CUP,
Rainbow, excel stat and hydrological, meteorological, spatial data. The methodology of
this work were the following: data collection, data preparation and quality assurance, data
analysis and model setup, running model, model performance evaluation and model result
interpretation. The total drainage area of the watershed was 2060.792 km
2
. Simulation of
the streamflow of Meki River watershed situated in central rift valley basin for the period
from 1993 – 2010 and sediment yield was computed by developing sediment rating curve
for the comparison of sediment yield produced from rating curve and sediment produced
by SWAT simulation. The model was calibrated by adjusting sensitive parameters for
observed stream flow data from 1993 – 2003 and validation was done using observed data
from 2004 – 2010. The highest flow sensitive parameter was the curve number (CN2),
Available water capacity of the soil layer (SOL_AWC) and Manning's "n" value for
overland flow (OV_N). The model performance was checked by statistical model
performance evaluation such as the coefficient of determination (R
2
), Nash – Sutcliffe
model efficiency (NSE) and percent bias. From the results of stream flow calibration and
validation R² = 0.81, NSE = 0.76, Pbias =18 and R² = 0.81, NSE = 0.74 Pbias =17.1
respectively. The total annual runoff and sediment yield produced by SWAT simulation was
367.95mm and 75.896 ton/ha/yr. respectively. The simulation results showed that applying
scenario USLE_P, conservation structure (contour ploughing and terracing with contour)
reduced the current sediment yield by 25.84% and 13.97% respectively and using scenario
filter strips reduced the current sediment yield by 68.47%. More research was necessary
to forecast sediment yield and runoff of each sub-basin for daily and monthly time step
under different land use/land cover scenario to improve decision making of the stake
holder.
