Abstract:
Abstract
Land degradation caused by soil erosion has become one of the major
constraints-of agricultural development in Ethiopia threatening the well being of
many people living in rural areas under subsistence agriculture. Moreover,
erosion has become one of the most serious problems in areas of water
development due to silt loads in irrigation canals, diversion structures and
storage reservoirs.
Effective watershed planning requires understanding of runoff and erosion rates
at the plot, on hill slopes, and at small catchments scales and how these vary
spatially and temporally in the watershed. Therefore to account for this spatial
and temporal variability of the watershed hydrologic characteristics, Soil and
Water Assessment Tool (SWAT) has been used to model the hydrologic
variables (suface run off, sediment yield, sediment load, etc.) at Bilate watershed. Therefore the main aim of this thesis is to identify the potential erosion sensitive
areas that have critical sediment generating sub watersheds that actually
demand immediate management treatment to minimize or even to stop the risk
of erosion.
The model was calibrated and validated against measured flow and sediment
data at Alaba Kulito outlet of Bilate watershed. Except manual stream flow
calibration where the calibration efficiencies are found to be poor, the overall
calibration and validation results showed model efficiencies within the
permissible limit, and this in turn showed a good match between measured and simulated flow as well as suspended sediment load of the watershed (See
sections 4.4 and 4.5). simulated flow as well as suspended sediment load of the watershed (See
sections 4.4 and 4.5). identified and three management scenarios, i.e., using field filter strips, foresting
or planting grass and contour bands have been suggested to minimize or
alleviate erosion hazards of these critical sub watersheds in particular and the
watershed in general. Therefore the sediment yield reduction due to 5m filter strips is 59.2%; due to
1 Om filter strip is 72. 7%; that due to contour bands is about 50% and 100% land
Lise improvement (afforestation) could yield ne9ligible sediment.
