Abstract:
Soil erosion modeling is a significant tool for viable conservation of natural, agricultural and built up
environments. In this thesis, Soil Erosion modeling of Nashe watershed was done to assess where and
when soil erosion potentials has occurred. The study was carried out using SWAT model with GIS
interface..
The general objective of this study was to estimate spatial and temporal patterns of soil erosion of Nashe
watershed physical based SWAT model. The SWAT (Soil and Water Assessment Tool) with GIS interface
which is used to delineate the watershed and extract networks for sub basin watershed. This study assess
sediment yield from Nashe watershed at outlet. The stream flow was calibrated for eleven years (1991-
2001) and validated seven years (2002-2008) at Nashe station using SWAT-CUP to estimate performance
of the model. The suspended sediment was generated by rating curve to compare with sediment
suspended simulated by SWAT and showed that acceptable result. In addition, from simulated suspended
sediment by SWAT, sediment yields simulated for sub-watershed. Based on simulated sediment yields
prone soil erosion of watershed were identified.
The model was successfully calibrated and validated for flow to estimate sediment yield. The model
performance for calibration and validation also has been evaluated by using statistical parameters. Flow
calibration gave coefficient of determination (R2
) and Nash-Sutcliffe simulation efficiency (ENS) 0.79 &
0.75 respectively. Flow validation gave 0.71 and 0.65 for R2 and ENS values respectively. Both calibration
and validation results indicate that the observed values show good agreement with simulated flow. The
SWAT model yields average annual sediment of 60.97 ton/ha for study area.
The annual sediment yield of Nashe sub basin has been obtained from stream flow simulated
results. Sediment yield from each sub watershed were also determined and prone soil erosion
area has been identified. The erosion prone area which needs immediate soil and water conservation
measure in Nashe watershed was identified. The sub watershed (75-150 ton/ha sediment yield) has been
identified as Severe soil erosion prone area, priority were needed for conservation measures
