4. Conclusion and recommendations
Runoff and suspended sediment concentration (SSC) were monitored at the
outlets of three main sub-watersheds of Koga catchment, North-Western
Ethiopian highlands during 2016-2017. The WATEM/SEDEM model was
calibrated to quantify the effect of SWC measures on soil erosion and
sediment yield. WATEM/SEDEM generally underestimated the effect of SWC
measures in controlling soil erosion and sediment yield in all
sub-watersheds. Soil erosion and sediment yield values were highly
variable across study sub-watersheds. This is most likely due to the
effect of SWC measures as well as biophysical characteristics such as
topography, land use and soil types. The integrated use of bund
structures, contour cultivation, strip cropping and grass strips had the
highest impact on controlling soil erosion and sediment yield.
Integration of bunds with one or more agronomic and vegetative measures
shows a higher effect on soil erosion and sediment yield in the study
sub-watersheds. This emphasises that the use of bund structures alone is
not sufficient as conservation strategy to control runoff and soil
erosion in NW Ethiopian highlands. This study demonstrates that the
harmful effects of soil erosion remain significant in Koga catchment and
the Koga reservoir at the outlet of Koga river is highly affected by
sedimentation. The calibration of WATEM/SEDEM at sub-watershed level has
provided good model performance for simulated erosion and sediment
yields. Therefore, WATEM/SEDEM adequately represents the underlying
erosion and sedimentary processes and can be further used to evaluate
the impacts of land use change and existing or new SWC scenarios. The
model output results emphasises the importance of integrated use of
conservation strategies to reduce soil erosion and sediment delivery.
Using a spatially explicit modelling approach, as done in this study,
increases insight in the spatially explicit effect of various measures
on erosion rates, as opposed to measurement of sediment yield at the
outlet of a catchment.