Modeling Sediment Load And Runoff Generation In Cheleleka Wetland Watershed Southern Ethiopia

Poor land use practice and improper management systems have played a significant role in causing high soil erosion and sediment transport on the Ethiopian highlands. The objectives of this study were to analyze LULC change in the past three decades, to quantify runoff, and sediment yield, to map the spatial distribution of sediment sources and prioritize areas for management intervention using SWAT model. Daily metrological data, soil data, stream flow data and land use land cover data were used to run the SWAT model. The coefficient of determination (R2) and Nash-Sutcliffe (ENS) were used to evaluate model calibration and validation. A sensitivity analysis was performed to identify the key sensitive parameters that are responsible for change in the watershed. Thirteen highly sensitive parameters were identified for stream flow. Results from the model outputs showed an increasing trend of sediment yield and runoff for past 22 years. Annual sediment yield was 9.56 t/ha in 1995, 15.63t/ha in 2003 and 26.42 t/ha in 2017. The possible reasons for increasing of annual sediment yield could be conversion of natural vegetation to cultivated land, bare land and settlements. In 1995 the Sub watersheds that are found in the upper which is sub watershed 24,18, 6 and sub watershed 16 are the highest contributors of sediment load to the wetland. In 2003 sub watershed 3,6 and 16 were generate more sediment and in 2017 sub watershed 2 and 3(in the upper part of the catchments) generated 84t/ha and 35t/ha respectively to the wetland. The annual average runoff generated from all watersheds estimated in 1995 and 2017 independently were 83.47mm and 90.65mm, respectively. In 2017 sub watersheds 6 (‘Wosha seyama’), 18 (‘abaye’) and 2 (‘lower lango’) were generated more runoff to the wetland. These sub watersheds are found on the upper part of the catchments which have slope of >20%. Higher the value of runoff related with soil type and conversion of natural vegetation and it has great effect for increasing of runoff to the wetland. Based on these findings, it is concluded that the rapid land use land cover change and increasing runoff in the study area significantly contributed to the sediment load to Cheleleka wetland. Therefore, the LULC change and lack of soil and water conservation practices are responsible for intensifying the level of potential annual sediment yield from uplands and Finally it is recommended that integrated watershed management could be implemented in these sub watersheds by encouraging the local people to participate in the management process.

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