Assessing soil erosion risk in a peri-urban catchment of the Lake Victoria basin

Gyaviira Ssewankambo; Isa Kabenge; Prossie Nakawuka; Joshua Wanyama; Ahamada Zziwa; Yazidhi Bamutaze; David Gwapedza; Carolyn Tally Palmer; Jane Tanner; Sukhmani Mantel; Bezaye Tessema

doi:10.1007/s40808-022-01565-6

Assessing soil erosion risk in a peri-urban catchment of the Lake Victoria basin

Model Earth Syst Environ. 2023;9(2):1633-1649. doi: 10.1007/s40808-022-01565-6. Epub 2022 Oct 29.

Affiliations

¹ P.O Box 7062, Kampala, Uganda Department of Agricultural and Biosystems Engineering, Makerere University.
² P.O Box 7062, Kampala, Uganda Department of Geography, Geo-Informatics and Climate Sciences, Makerere University.
³ P.O. Box 94, Makhanda, Eastern Cape South Africa Institute for Water Research, Rhodes University.
⁴ P.O. Box 1176, Addis Ababa, Ethiopia Water and Land Resource Centre, Addis Ababa University.

Abstract

Soil erosion and sedimentation contribute to deteriorating water quality, adverse alterations in basin hydrology and overall ecosystem biogeochemistry. Thus, understanding soil erosion patterns in catchments is critical for conservation planning. This study was conducted in a peri-urban Inner Murchison Bay (IMB) catchment on the northern shores of Lake Victoria since most soil erosion studies in Sub-Saharan Africa have been focused on rural landscapes. The study sought to identify sediment sources by mapping erosion hotspots using the revised universal soil loss equation (RUSLE) model in appendage with field walks. RUSLE model was built in ArcGIS 10.5 software with factors including: rainfall erosivity, soil erodibility, slope length and steepness, land cover and support practices. The model was run, producing an erosion risk map and field assessments conducted to ground-truth findings and identify other hotspots. The percentage areas for RUSLE modelled erosion rates were: 66.8% for 0-2 t ha^-1 year^-1; 10.8% for 2-5 t ha^-1 year^-1; 10.1% for 5-10 t ha^-1 year^-1; 9% for 10-50 t ha^-1 year^-1 and 3.3% for 50-100 t ha^-1 year^-1. Average erosion risk was 7 t ha^-1 year^-1 and the total watershed erosion risk was 197,400 t year^-1, with croplands and steep areas (slope factor > 20) as the major hotspots (> 5 t ha^-1 year^-1). Field walks revealed exposed soils, marrum (gravel) roads and unlined drainage channels as other sediment sources. This study provided the first assessment of erosion risk in this peri-urban catchment, to serve as a basis for identifying mitigation priorities. It is recommended that tailored soil and water conservation measures be integrated into physical planning, focusing on identified non-conventional hotspots to ameliorate sediment pollution in Lake Victoria.

Keywords: Geographical information system; Inner Murchison Bay catchment; Land use land cover; RUSLE.

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