Abstract:
Land degradation is a series threat in the Ethiopian high lands in general and in Gumara
watershed in particular reflected in the form of soil erosion and soil fertility decline. Sheet
and rill erosion are considerably the most widespread accelerated water erosion and their
combined effect significantly affect agricultural production and productivity.
The objective of the study is to predict sediment yield and runoff, to identify spatial
distribution of sediment source areas and propose high impact management options to
control soil erosion and sedimentation problems in Gumara watershed.
SWAT (Soil and Water Assessment Tool) was employed for modeling runoff and
sediment yield in Gumara watershed .The model was calibrated and validated against
measured flow and sediment data. Both calibration and validation i-�;ults showed good
,·
match between measured and simulated flow and suspended sediment.
The model prediction result indicated that about 72 % of the Gumara watershed is erosion
potential area contributing high sediment yield exceeding the tolerance limit (soil
formation rate) in the study area. Out of 30 sub watersheds, 18 of the sub watersheds were
found to be critical contributing high sediment yield with an average annual sediment load
ranging from 11 to 22 ton/ha/yr. The result of the model was verified by detail field
observation that sub watersheds with average annual sediment yield exceeding the
tolerable limit were identified as high erosion source area which additionally justifies the
model's ability to replicate the erosion processes in the watershed. After calibration and
validation of SWAT model, the impacts of watershed management interventions were
tested to reduce sediment loads from critical sub watersheds. The simulation result
indicated that implementing vegetation filter strip can reduce sediment yield by 58 to 74 percen
