ESTIMATION OF SOIL LOSS USING REVISED UNIVERSAL SOIL LOSS EQUATION IN BORKENA RIVER CATCHMENT, UPPER AWASH BASIN, AMHARA REGION, ETHIOPIA

Abstract

Soil Erosion is one of the most important environmental problems that poses serious challenge to food security and future development prospects of Ethiopia. To tackle this problem proper soil conservation planning is necessary. The objective of this study was to estimate soil loss rates in the Borkena watershed in South Wollo Highlands. For soil conservation soil loss estimation using the Revised Universal Soil Loss Equation (RUSLE) based on satellite remote sensing and geographical information systems (GIS) was used for conservation planning. The input data for the model includes Monthly precipitation, soil map, a 30 x 30m digital elevation model, land-cover map, and slope steepness. Homogeneity and consistency test were undertaken, the collected data were homogeneous and the consistency of the rainfall was linear. Based on the level of soil erosion rates, the study area was divided into seven priority categories for conservation interventions. The finding indicates that about 85% of total area suffer a high, very high, severe or very severe to extremely severe erosion risk, mainly in the steeper slope banks of tributaries where steep lands are cultivated or overgrazed. The total soil loss estimated to be 711,525.5 t/ha/y with mean annual soil loss of 23.7t/ha/y which falls under high soil loss category. Critical sub-watersheds that require conservation intervention include, SW6, SW22, SW23, SW19, SW7, SW5, SW20, SW21, SW3, SW25, SW18, SW4, SW14, SW12, and SW24 with annual average soil loss ranging between 20.8 and 55.43t/ha/y were selected and recommended to receive appropriate management measures in order to reduce the soil losses to tolerable level. The SWAT model is calibrated and validated for flow and sediment at the Maybar gauging station. The model resulted with the annual average sediment value of 27.46 ton/ha/yr and 29.5 ton/ha/yr at maybar catchment and Borkena watershed respectively.