USLE-Based Assessment of Soil Erosion by Water in the Nyabarongo River Catchment, Rwanda

Abstract

Soil erosion has become a serious problem in recent decades due to unhalted trends of unsustainable land use practices. Assessment of soil erosion is a prominent tool in planning and conservation of soil and water resource ecosystems. The Universal Soil Loss Equation (USLE) was applied to Nyabarongo River Catchment that drains about 8413.75 km2 (33%) of the total Rwanda coverage and a small part of the Southern Uganda (about 64.50 km2) using Geographic Information Systems (GIS) and Remote Sensing technologies. The estimated total annual actual soil loss was approximately estimated at 409 million tons with a mean erosion rate of 490 t·ha−1·y−1 (i.e., 32.67 mm·y−1). The cropland that occupied 74.85% of the total catchment presented a mean erosion rate of 618 t·ha−1·y−1 (i.e., 41.20 mm·y−1) and was responsible for 95.8% of total annual soil loss. Emergency soil erosion control is required with a priority accorded to cropland area of 173,244 ha, which is extremely exposed to actual soil erosion rate of 2222 t·ha−1·y−1 (i.e., 148.13 mm·y−1) and contributed to 96.2% of the total extreme soil loss in the catchment. According to this study, terracing cultivation method could reduce the current erosion rate in cropland areas by about 78%. Therefore, the present study suggests the catchment management by constructing check dams, terracing, agroforestry and reforestation of highly exposed areas as suitable measures for erosion and water pollution control within the Nyabarongo River Catchment and in other regions facing the same problems.

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

“…In line with the findings of our study, Abate [5] reported that the steep slopes are attributed to high soil loss rate and aggravated soil erosion risk in the Borena Woreda of South Wollo Highlands of Ethiopia. A recent report by Karamage et al [133] for the Nyabarongo River Catchment, Rwanda, also agrees with the present study's findings, showing a higher soil erosion in the very steep slope areas contributing about 73.5% of the total soil loss. They strongly suggested construction of erosion control structures and rehabilitation of vegetation covers as a solution to reduce the soil loss in the catchment area [133].…”

“…A recent report by Karamage et al [133] for the Nyabarongo River Catchment, Rwanda, also agrees with the present study's findings, showing a higher soil erosion in the very steep slope areas contributing about 73.5% of the total soil loss. They strongly suggested construction of erosion control structures and rehabilitation of vegetation covers as a solution to reduce the soil loss in the catchment area [133]. The fourth, fifth and sixth conservation levels accounting for 21,104.37 ha (8.88% of the total study area) need of minor SWC measures.…”

“…It is also higher than the findings of earlier researchers in other areas in Ethiopia [27,33,127], and elsewhere in the world [128,129]. On the contrary, the present study results are lower than the findings across the Northwestern Ethiopia highland [130], and other similar studies' findings [131][132][133]. Several previous studies suggested that vulnerability to a higher rate of water-induced soil erosion occurring in eastern Ethiopia's highland is associated with the adverse effects of LULC changes, an unsustainable land management, and less emphasis is given to SWC practices [7,134,135].…”

Soil Erosion Risk Assessment in Uganda

“…Lake Victoria is the world's second largest freshwater lake with a surface area of about 68,000 km 2 shared by Kenya, Tanzania, and Uganda. Lake Victoria was listed among the top 10 severely polluted world water bodies [10,11]. High levels of eutrophication and water hyacinth infestation in Lake Victoria were attributed to soil erosion due to unsustainable agricultural practices in the East African region [12,13].…”

Change Analysis on Soil Erosion of Fujian Province From 1990 to 2015

“…This is mainly due to the simple, robust form of the equations as well as their success in predicting the average, long-term erosion. USLE and RUSLE have been applied to various spatial scales and region sizes in different environments worldwide (Gericke, 2015;Ali and Hagos, 2016;Karamage, et al, 2016;Jiang, et al, 2016;Lin et al, 2016).…”