Comprehensive assessment of soil erosion risk for better land use planning in river basins: Case study of the Upper Blue Nile River

Abstract

In the drought-prone Upper Blue Nile River (UBNR) basin of Ethiopia, soil erosion by water results in significant consequences that also affect downstream countries. However, there have been limited comprehensive studies of this and other basins with diverse agroecologies. We analyzed the variability of gross soil loss and sediment yield rates under present and expected future conditions using a newly devised methodological framework. The results showed that the basin generates an average soil loss rate of 27.5thayr and a gross soil loss of ca. 473Mtyr, of which, at least 10% comes from gully erosion and 26.7% leaves Ethiopia. In a factor analysis, variation in agroecology (average factor score=1.32) and slope (1.28) were the two factors most responsible for this high spatial variability. About 39% of the basin area is experiencing severe to very severe (>30thayr) soil erosion risk, which is strongly linked to population density. Severe or very severe soil erosion affects the largest proportion of land in three subbasins of the UBNR basin: Blue Nile 4 (53.9%), Blue Nile 3 (45.1%), and Jema Shet (42.5%). If appropriate soil and water conservation practices targeted ca. 77.3% of the area with moderate to severe erosion (>15thayr), the total soil loss from the basin could be reduced by ca. 52%. Our methodological framework identified the potential risk for soil erosion in large-scale zones, and with a more sophisticated model and input data of higher spatial and temporal resolution, results could be specified locally within these risk zones. Accurate assessment of soil erosion in the UBNR basin would support sustainable use of the basin's land resources and possibly open up prospects for cooperation in the Eastern Nile region.

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

“…To discuss the differences in discharge and runoff coefficients between the two watersheds, we note that prior experimental studies have found that the main runoff generation mechanism in the (sub) humid Ethiopian highlands is saturation excess runoff [15,20,22,24,[45][46][47][48]. Saturated excess overland flow occurs at locations either where the soils become saturated above an impeding layer or where the regional groundwater reaches the surface.…”

“…Fifty-eight percent of the Chemoga watershed, a part of the Blue Nile basin in Ethiopia, lost more than 80 Mg ha −1 y −1 of soil [14]. About 39% of the Blue Nile basin area contributed more than 30 Mg ha −1 y −1 of soils [15]. Based on the findings of [16], upland soil losses in the Lake Tana basin of the Blue Nile were 30 Mg ha −1 y −1 on average, most of which was deposited on the plains around Lake Tana.…”

“…Most of the factors contributing to high soil erosion rates and land degradation are human induced [15,19]. To meet the increasing demand for food and fuel by the rapidly growing population, the land has been deforested and the subsequent loss of organic matter has led to a lower soil aggregate strength and finer soils.…”

Economic Evaluation of Hydrological Ecosystem Services in Mediterranean River Basins Applied to a Case Study in Southern Italy

“…In the literature there are different C factor values in relation to soil use [12], plant species and agricultural practices [55]. Only soil-related values were used in this work due to the lack of site-specific knowledge on soil tillage, pruning and green (or crop) residue management.…”

“…The latter is usually used for estimating the soil amount removed by water runoff [11]. Soil use also influences the main terms of the water balance, i.e., canopy interception, evapotranspiration, infiltration, soil water storage, and surface outflow [12][13][14]. Moreover, the above parameters are also related to the characteristics of vegetation (species, crop management, leaf area, root depth, crop height) and soil (organic matter content, hydraulic conductivity, infiltration capacity, apparent density, porosity).…”