Estimation of soil erosion using USLE and GIS in Awassa Catchment, Rift valley, Central Ethiopia

Abstract

In central part of the Main Ethiopian Rift, population increase is forcing farmers to expand their land by clearing forests, bushes and scrubs for crop cultivation, construction purposes and for fuel as energy source. Thus, loss of agricultural lands is increasing in the catchment. Therefore, estimation of soil erosion in Awassa catchment, Ethiopia is very important to make sound environmental management strategies and land use planning. In this context, Universal Soil Loss Equation (USLE) has been adopted to estimate soil erosion for sheet, rill and inter-rill. All these thematic layers were prepared in a Geographical Information System (GIS) using various data sources and data preparation methods. The soil erosion map was prepared by GIS layers over lapping method which ultimately estimated soil erosion rate of study area. The study revealed that 97% of the study area is characterized by 0–10tha−1year−1 soil erosion rate, whereas 3% of the study area is characterized by 10–202tha−1year−1 soil erosion rates. When estimated for soil erosion, it was found that out of the whole catchment, 30km2 was under high to extremely high soil erosion rate (91–202tha−1year–1). The outcome of research also showed that the study areas having six ordinal classes of soil erosion risk zone, e. g., extremely high risk (91–202), extreme risk (55–91), very high risk (30–55), high risk (10−30), moderate risk (5–10) and low risk (0–5) with corresponding percentage of area falling, 0.18, 0.26, 0.43, 1.62, 2.68, and 94.83, respectively. From the level of soil tolerance limits, it appears that the amount of soil loss is tolerable at its current situation.