Effects of Soil and Water Conservation Practices on Runoff, Soil and Nutrient Losses in Alekt Wenz Watershed, Ethiopian Highland

Abstract

Land degradation caused by soil erosion is a serious problem in northwestern Ethiopian highlands. To reduce the adverse impact of land degradation, soil and water conservation (SWC) measures were implemented. The presented study investigated the hydrological responses of SWC measures implemented in two nested watersheds situated in the northwestern Ethiopian highland. Rainfall, streamflow, sediment concentration, and sediment-associated and dissolved nutrient of N and P for 2015 and 2016 rainy periods were collected and analyzed. The watersheds received 665 mm in 2015 and 795 mm rainfall in 2016 from May to September. The median infiltration rates for treated and untreated watershed were 22 mm hr−1, and 19 mm hr−1 respectively. The direct runoff from treated watershed was 8.5 mm yr−1 for 2015 and 9.6 mm yr−1 for 2016. This is lower than the untreated watershed, which responded 17.3 mm yr−1 for 2015 and 15.3 mm yr−1 for 2016. The base flow from treated watershed was 180.7 mm yr−1 for 2015 and 212 mm yr−1 for 2016. It was higher than the untreated watershed, which responded 69.8 mm yr−1 for 2015 and 195.4 mm yr−1 for 2016. This figure shows that implemented SWC measures reduced the runoff responses by two-fold. Similarly, the SWC measures reduced sediment yield. The sediment yield from treated watershed was 2.4 ton ha−1yr−1 and 2.1 ton ha−1yr−1 in the year 2015 and 2016, respectively. This is lower than the untreated watershed that lost 6 ton ha−1yr−1 and 8.5 ton ha−1yr−1 in the year 2015 and 2016, respectively. The effectiveness of the SWC measures between the two watersheds was statistically significant with a significance level of 5%. However, it is important to investigate the long-term effects of SWC in reducing soil and nutrient losses.