Sediment Yield Source Identification in Gilgel Gibe-I Catchment Using GIS-based RUSLE and SEDD Models for Soil Conservation Planning, South West Ethiopia

摘要

Onsite and off-site effects of soil erosion are the biggest global environmental problems. Some of the offsite problems are silting of dams and reservoir, disruption of lake ecosystems, and increased downstream flooding. Gilgel Gibe-1 catchment has been also subjected to sedimentation and other offsite problems. This study was aimed to identify the source of sediment yield in Gilgel Gibe-1 catchment using GIS-based RUSLE and SEDD models for soil conservation planning. Primary and secondary data from different sources were used to estimate soil loss from the catchment using GIS-based RUSLE model. Rainfall-runoff erosivity, soil erodibility, topographic effect, surface coverage, and land management practice of the catchment were used as an input to RUSLE model. Sediment Delivery Ratio was estimated using the SEDD model. The result of this study shows the mean annual soil loss of the catchment is 62.98 t ha -1 year -1 which are about 26.56x106 t year -1 and the mean sediment delivery ratio is 0.1367. The mean annual sediment yield of the catchment is 8.61t ha -1 year -1 and the overall catchment area contributes about 3.63x106t year -1 sediment to the reservoir at the dam site. On the bases of mean annual sediment yield, a source of sediment yield areas are identified and prioritized. Accordingly, SW4, SW5, SW3, SW6, SW7, SW8, SW9, SW2, and SW1 got priority level in the order of 1 to 9. Sediment yield 10 t ha -1 year -1 covers 15.75% of the catchment area and 0-5 t ha -1 year -1 covers 78.22%, of the catchment. The result of this study indicates the catchment and reservoir are under the problem of soil loss and siltation, respectively. Therefore, it is recommended that immediate action, soil, and water conservation measures, should be taken in the catchment according to the priority of sub-watersheds and further detail study is suggested with the support of experimental test plots.