How soil conservation affects the catchment sediment budget – a comprehensive study in the north Ethiopian highlands

Abstract

An overall approach to assess the effectiveness of soil conservation measures at catchment scale is the comparison of sediment budgets before and after implementation of a catchment management programme. In the May Zeg-zeg catchment (187 ha) in Tigray, north Ethiopia, integrated catchment management has been implemented since 2004: stone bunds were built in the whole catchment, vegetation was allowed to re-grow on steep slopes and other marginal land, stubble grazing abandoned, and check dams built in gullies. Land use and management were mapped and analysed for 2000 and 2006, whereby particular attention was given to the quantification of changes in soil loss due to the abandonment of stubble grazing. Sediment yield was also measured at the catchment's outlet. A combination of decreased soil loss (from 14·3 t ha -1 y -1 in 2000 to 9·0 t ha -1 y -1 in 2006) and increased sediment deposition (from 5·8 to 7·1 t ha -1 y -1 ) has led to strongly decreased sediment yield (from 8·5 to 1·9 t ha -1 y -1 ) and sediment delivery ratio (from 0·6 to 0·21). This diachronic comparison of sediment budgets revealed that integrated catchment management is most effective and efficient and is the advisable and desirable way to combat land degradation in Tigray and other tropical mountains. policy information, qualitative (process interaction) and quantitative (process rates), about erosion and sediment deposition.Geomorphologists use sediment budgets to investigate the relative importance of the different components and their Figure 9. Sediment budgets for MZZ catchment in 2000 (left) and 2006 (right) with computation of sediment sources and sinks. Width of arrows is proportional to sediment masses involved.

Prediction of soil and water conservation structure impacts on runoff and erosion processes using SWAT model in the northern Ethiopian highlands

“…The intervention of SWC measures by the mobilization of the community has a significant soil loss reduction to protect their land from the rainfall-driven soil erosion. The effectiveness of SWC on runoff and sediment yield reduction has been reported in other studies in northern Ethiopia (Gebremichael et al 2005;Haregewyn et al 2005;Descheemaeker et al 2006;Mitiku et al 2006;Nyssen et al 2007Nyssen et al , 2009Dagnew et al 2015Dagnew et al , 2017.…”

Sediment dynamics and the role of flash floods in sediment export from medium-sized catchments: a case study from the semi-arid tropical highlands in northern Ethiopia

“…In addition, the cropland is generally sown at the beginning of the rainy season. At this time the fields have undergone at least two tillage operations, are bare and offer little resistance to splash and runoff erosion (Nyssen et al 2009a). Due to the long dry season and the large numbers of grazing livestock, most hillslopes are almost bare at the start of the rainy season.…”

“…Soil and water conservation (SWC) measures were found to have a profound impact on the SSY of small catchments in the Ethiopian highlands (Haregeweyn et al 2008;Nyssen et al 2009a). However, in this study, no significant correlation was found between all SSY-season values and the estimated stone bund (SB) density of each subcatchment (τ = -0.05, p = 0.784).…”

“…SWC-measures, such as stone bunds and exclosures, significantly reduce hillslope erosion and sediment connectivity (e.g. Descheemaeker et al 2006;Nyssen et al 2009a) and probably have a reducing effect on the sediment export at the beginning of the rainy season. A better, however still insignificant, correlation exists between the mass of sediments transported in P1 and SB density (τ = -0.26, p = 0.12).…”

“…Although the potential of these rehabilitation measures to reduce runoff and soil erosion have been studied at the hillslope and small catchment scale (e.g. Descheemaeker et al 2006;Haregeweyn et al 2008;Nyssen et al 2009a), the integrated effect of these measures at the medium-sized catchment scale is not well understood. The response of catchments to soil erosion and human interventions is often complex due to scale effects which can buffer changes in sediment supply (Walling 1983;Trimble 1999;Verstraeten et al 2002;Walling 2006;de Vente et al 2007).…”