Investigating Soil Erosion And Soil Conservation In Tropical (Sub) Humid Highlands: Findings From Debre Mawi, Ethiopia

Abstract

Soil erosion and soil conservation are two of the biggest challenges for farmers, economic development plans, and academics in rural agricultural watersheds worldwide. This study compares erosion risk estimates and analyzes the underlying framework of models being used around the world exemplified by the Universal Soil Loss Equation (USLE) and infiltration excess runoff principles. Variations in modelled erosion processes in the Debre Mawi, Ethiopia were compared to field observations, community perceptions, and results from a saturation excess erosion model. In the first analysis, USLE did not capture the spatial representation of erosion due its misrepresentation of the main hydrological processes in humid highland watersheds: saturated pathways, subsurface flow, and gully formation. The investigation also analyzed erosion risk perceptions to better evaluate opportunities for community land management. Interviewed farmers considered themselves heterogeneous actors who have personal reservations to address before being able to work cooperatively. Also, they view government efforts as relevant but advocated more integration of farmers' ideas. Their perception of risk is based on how their lives are changing and what they anticipate will be their best for their families' future. Lastly, these insights were used to model runoff and sediment transport in this watershed with an adjusted Parameter Efficient Distributed Model. The watershed receives unpaved road flow contributions, so an integrated flow contribution needed to be represented. The added Hortonian flow adjustment to the PED model integrated both infiltration- and saturation-excess flow regimes. The discharge (NSE = 0.70) and sediment concentrations (NSE = 0.71) results on a daily scale demonstrated progress from previous work but need to better address high influxes of sediment from gullies. The results show that a more comprehensive approach to spatial distribution of erosion estimates is possible and necessary for more effective soil and water conservation in the sub humid Ethiopian Highlands. Keywords: Sediment transport, USLE, Community knowledge, Hortonian flow, Dunnean flow