Soil erosion assessment and crop management as strategies for watershed management improvement

Abstract

Land degradation and low agricultural productivity are severe problems in the highlands of Ethiopia. Various soil and water conservation (SWC) strategies have been in use to tackle soil erosion. However, the effectiveness of SWC measures on runoff dynamics and sediment load in terms of their medium- and short-term effects has not been sufficiently studied. A study was conducted in 2011 through to 2015 in the Gumara-Maksegnit watershed to study the impacts of SWC structures on runoff and soil erosion processes using SWAT model. The study was conducted in two adjacent watersheds where in one of the watersheds SWC structures were constructed (Treated watershed-TW) in 2011, while the other watershed was a reference watershed without SWC structures (Untreated watershed-UW). Runoff and sediment yield were compared based on the observations and model simulations. The result of runoff simulation indicated that SWAT can simulate the hydrological regime for both watersheds. The daily runoff calibration result for the TW and UW showed good correlation between the predicted and the observed data (R2 = 0.78 for the TW and R2=0.77 for the UW).The validation result also showed good correlation with R2 values of 0.72 and 0.70 for the TW and UW, respectively. Sediment yield calibration and validation results showed modest correlation between the predicted and observed sediment yields with R2 values of 0.65 and 0.69 for the TW and UW for the calibration and R2 values of 0.55 and 0.65 for the TW and UW for the validation, respectively. The model results indicated that SWC structures considerably reduced soil loss by as much as 25-38% in the TW. The study proved that SWAT performed well for both watersheds and can be a potential instrument for out and up-scaling to assess and design SWC structures impact in the highlands of Ethiopia. The results confirmed that SWC structures have a significant impact to prevent land degradation in the Ethiopian highlands.