Potential soil erosion estimation and area prioritization for better conservation planning in Gumara watershed using RUSLE and GIS techniques’

Abstract

Background: Water induced soil erosion has been continued to threaten the land resources in sub humid northwestern highlands of Ethiopia. Soil and water conservation measures have been implemented without site-specific scientifically quantified soil erosion data and priority bases. In this regard, quantitative analysis of soil erosion and its spatial variation plays a decisive role for better evidence and priority based implementation. Thus, this study aimed to estimate potential soil loss, identify hotspot areas, and prioritize for conservation measures in Gumara watershed using RUSLE, GIS and remote sensing techniques'. Result: The study result showed that soil loss due to water erosion was found to be a critical problem in the watershed. It ranges from nearly zero in gentle slope of forest lands to 442.92 t ha −1 year −1 on very steep slope cultivated lands. A total of 9.683456 million t of gross surface soil has been lost annually, with an average soil erosion rate of 42.67 t ha −1 year −1. Of which 62.1% was generated from cultivated land. The model result indicated a high spatial variability of soil erosion within the watershed. High intensity of soil erosion has been principally attributed to slope and land use/covers. The study further estimated that about 63.1% of the total soil loss was generated from only 29.3% of the area delineated as very severe soil erosion severity class. Soil erosion rate for 71.7% of the watershed area was beyond the maximum tolerable soil erosion limit estimated for Ethiopian highlands (> 18 t ha −1 year −1). The subwatershed severity class map revealed that 3814 ha of the sub-watershed area was evaluated as very severe level of soil erosion severity class. Conclusion: Soil erosion in the watershed has been a threatening problem for agricultural production to day, its sustainability and to be worsening in the future unless remedial measures were taken, mainly due to human intervention. Therefore, Gumara watershed needs immediate intervention for better conservation planning by considering identified priority classes and hotspot areas.

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

“…Relatively less eroded areas were situated in the lower elevations in the eastern and western parts of the sub-basin, where the slope inclination is ranging from nearly zero to ten percent. Similar results have been reported by the earlier studies that attributed lower soil loss rate to gentle slopes while a higher soil loss in steep slope areas [18,[120][121][122][123].…”

“…Our findings coincide with those of the recent study by Yesuph and Dagnew [128] who showed that the cropland under a mono-cropping and intensive cultivation in the upslope areas were responsible for severe soil erosion in the Beshillo Catchment of the Blue Nile Basin. Validating the present study's findings, Belayneh et al [120] also pointed out that cultivated land with a mean erosion rate of 45.68 t ha −1 yr −1 accounted for 62.06% of the total soil loss from the Gumara Watershed of the northwestern Ethiopia highland. The landscape that had experienced the LULCC during the period of the assessment accounted for about 43.48% of the total study area, of which about 11.44% revealed an increase in the estimates of soil loss of 75.66 t ha −1 yr −1 .…”

Effects of soil and water conservation practices on soil physicochemical properties in Gumara watershed, Upper Blue Nile Basin, Ethiopia

“…Cultivated land, forest land, grazing land, shrub/wood land, bare land, and built-up areas are the major land uses/covers in the watershed (Belayneh et al 2019). Of which the cultivated land covers 58.09%.…”

“…As part of the Ethiopian highlands, the Upper Blue Nile Basin experiences high soil erosion rate (0-200 tons ha −1 year −1 ) (Haregeweyn et al 2017) and 131 million tons of soil loss annually because of poor land use management systems (Betrie et al 2011). The Gumara watershed is part of this basin that is affected by high soil erosion (Belayneh et al 2019;Hurni et al 2005) and among the highest mean runoff portion in the basin (Haregeweyn et al 2016).…”

“…In the Gumara watershed like most northwestern highlands, different SWC structures were implemented by farmers through community mass-mobilization since 1995. However, soil erosion is still very high and a threatening problem for soil resource and agriculture (Belayneh et al 2019). In the sub-humid northwestern highlands, little attention has been given to SWC interventions and little information is documented on effectiveness of SWC measures (Haregeweyn et al 2015).…”