Impact of Soil Depth and Topography on the Effectiveness of Conservation Practices on Discharge and Soil Loss in the Ethiopian Highlands

Abstract

Abstract:Restoration of degraded landscapes through the implementation of soil and water conservation practices is considered a viable option to increase agricultural production by enhancing ecosystems. However, in the humid Ethiopian highlands, little information is available on the impact of conservation practices despite wide scale implementation. The objective of this research was to document the effect of conservation practices on discharge and sediment concentration and load in watersheds that have different soil depths and topography. Precipitation, discharge, and sediment concentration were measured from 2010 to 2012 in two watersheds in close proximity and located in the Lake Tana basin, Ethiopia: Tikur-Wuha and Guale watersheds. The Tikur-Wuha watershed has deep soils and a gentle slope stream channel. The Guale watershed has shallow soils and a steep slope stream channel. In early 2011, the local community installed upland conservation measures consisting of stone and soil bunds, waterways, cutoff drains, infiltration furrows, gully rehabilitation, and enclosures. The results show that conservation practices marginally decreased direct runoff in both watersheds and increased base flow in the Tikur-Wuha watershed. Average sediment concentration decreased by 81% in Tikur-Wuha and 45% in Guale. The practices intended to increase infiltration were most effective in the Tikur-Wuha watershed because the deep soil could store the infiltrated water and release it over a longer period of time after the rainy season than the steeper Guale watershed with shallow soils.

Spatial Modeling of Soil Erosion Risk and Its Implication for Conservation Planning: the Case of the Gobele Watershed, East Hararghe Zone, Ethiopia

“…Supporting the current study's findings, Tadesse et al [139] noted considerable improvement in the soil erosion and rehabilitation of degraded lands in the Yezat Watershed of North Western Ethiopia following implementation of integrated watershed development programs. Validating these findings, Akale et al [140] also reported that implementation of upland conservation measures significantly reduced the surface runoff and increased base flow in the Guale and Tikur-Wuha watersheds of the Ethiopian highlands.…”

Effect of Land Use and Land Cover Change on Soil Erosion in Erer Sub-Basin, Northeast Wabi Shebelle Basin, Ethiopia

“…The model was run to estimate the actual annual rates of soil loss in the study landscape for the years 2000 and 2018. The soil erosion risk within the study area was classified into eight categories, based on previous work by Uddin et al [5], and the estimated mean soil loss rates (t ha −1 y −1 ): very low (< 5), low (5-10), low medium (10)(11)(12)(13)(14)(15), medium (15)(16)(17)(18)(19)(20), high medium (20)(21)(22)(23)(24)(25), high (25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35), very high (35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50), and extremely high (>50). Areas with a mean annual soil loss rates lower than low were rated as tolerable soil loss limit [52].…”

“…Several previous studies highlighted the positive outcome of SWC measures for mitigating erosion risk, restoration of the degraded land while improving the soil fertility and land productivity [5,[35][36][37][38][39][40][41][42][43]. The design and implementation of SWC measures need a spatially intrinsic information on soil loss and severity levels erosion risk [18,47,99].…”

“…The Ethiopian highland, which covers about 44% of the country's total geographical area and sustains the livelihood of about 87% of the population, is the most eroded physiographical regions in the country [33][34][35]. The estimated annual soil loss from the highland areas varies widely from 200 t ha −1 y −1 to as high as 300 t ha −1 y −1 [36][37][38][39][40]. Intense rainfall, low vegetation cover, rugged topography, and anthropogenic factors are thought to be the most important factors contributing to a higher rate of soil erosion.…”

“…Intense rainfall, low vegetation cover, rugged topography, and anthropogenic factors are thought to be the most important factors contributing to a higher rate of soil erosion. Deforestation, agriculture land and urban expansion, cultivation in upslope areas, uncontrolled and overgrazing were the major anthropogenic drivers of soil erosion in the highland areas of the country [27,38,40]. A report from the Soil Conservation Research Program (SCRP) indicates that almost 50% of the Ethiopian highlands were seriously eroded, while 4% of the highland areas have reached a level of irreversibility that they will no longer give economic productivity in the foreseen future [38,39].…”