Abstract:
Elgo catchment is the main stream inflow to Lake Chamo, which provides a variety of ecosystem services. However, the contribution of sediment yield in the catchment is unknown. This study aim to quantify and map the sediment yield in Elgo catchment using In-situ measured data and sediment export model (InVEST). A non-linear power regression method was used to derive the stage-discharge rating curve and the discharge-suspended sediment concentration. The In-situ measured data from September-August 2019 at Elgo gauging station is used to calibrate the discharge-suspended sediment concentration rating curve and to validate the InVEST sediment delivery ratio (SRD) model. The discharge-suspended sediment concentration rating curve satisfactorily reproduced the volume, pattern and peak of the observed hydrograph with NSE of 0.76, and R2 of 0.95 during calibration period over the study area at the Elgo out let. The InVEST sediment delivery ratio (SRD) model was validated (R2 = 0.99 and NSE = 0.77). In order to identify the hotspots soil loss and sediment export areas, the annual soil loss and sediment export were quantified and mapped at pixel level (30x30m resolution) and the entire pixels within the Elgo catchment was classified into five soil risk classes: low (0-11 ton* ha−1* year−1), moderate (11-18 ton* ha−1* year−1), high (18-30 ton* ha−1* year−1), very high (30-50 ton* ha−1* year−1), and severe (>50 ton* ha−1* year−1). The maximum tolerable mean soil erosion limit found in literature review is 11 ton* ha−1* year−1, but the Elgo catchment erosion risk class 3, 4 and 5 are much higher than the limit. Generally, very few areas of the Elgo catchment are responsible for severe soil loss. For instance, severe erosion risk class 5 covers only 3.12 % of the entire watershed but it accounts about 29.39% of the total soil loss, whereas low soil loss class 1 cover about 76.95% of the Elgo catchment but contributed only 23.83 % of the soil loss. The overall annual soil loss over Elgo catchment was 5.129204*105 tone/312 km2. Therefore, prioritization of restoration areas based on the soil loss severity classes is vital. The geo-referenced prioritized micro catchments should be used as master plan during the implementation of sustainable land management.
