Estimation of Soil Erosion Dynamics in the Koshi Basin Using GIS and Remote Sensing to Assess Priority Areas for Conservation

Abstract

High levels of water-induced erosion in the transboundary Himalayan river basins are contributing to substantial changes in basin hydrology and inundation. Basin-wide information on erosion dynamics is needed for conservation planning, but field-based studies are limited. This study used remote sensing (RS) data and a geographic information system (GIS) to estimate the spatial distribution of soil erosion across the entire Koshi basin, to identify changes between 1990 and 2010, and to develop a conservation priority map. The revised universal soil loss equation (RUSLE) was used in an ArcGIS environment with rainfall erosivity, soil erodibility, slope length and steepness, cover-management, and support practice factors as primary parameters. The estimated annual erosion from the basin was around 40 million tonnes (40 million tonnes in 1990 and 42 million tonnes in 2010). The results were within the range of reported levels derived from isolated plot measurements and model estimates. Erosion risk was divided into eight classes from very low to extremely high and mapped to show the spatial pattern of soil erosion risk in the basin in 1990 and 2010. The erosion risk class remained unchanged between 1990 and 2010 in close to 87% of the study area, but increased over 9.0% of the area and decreased over 3.8%, indicating an overall worsening of the situation. Areas with a high and increasing risk of erosion were identified as priority areas for conservation. The study provides the first assessment of erosion dynamics at the basin level and provides a basis for identifying conservation priorities across the Koshi basin. The model has a good potential for application in similar river basins in the Himalayan region.

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

“…The results show that the erosion risk area increased by 19.67% of the total study area, and decreased by 9.53%, which shows that overall soil loss situation is worsening in the study area. These findings agree with those of the recent study by Uddin et al [90] who reported that the state of soil erosion risk in the Koshi Basin has been worsening following increase in the proportion of the eroded areas over 9.0% of the total basin area between 1990 and 2010. On the contrary, Wang et al [92] found improvement in the state of erosion risk in the Danjiangkou reservoir area, China, where the eroded areas have declined from 32.1% in 2004 to 25.43% in the 2010 study period.…”

“…On the contrary, Wang et al [92] found improvement in the state of erosion risk in the Danjiangkou reservoir area, China, where the eroded areas have declined from 32.1% in 2004 to 25.43% in the 2010 study period. Moreover, Jiang et al [16] reported that the eroded area has Therefore, since there is geospatial variation in soil erosion risk distribution across the watershed area, identification of priority area is the key factor for planning and implementing appropriate SWC [10][11][12][13][14][15][16][17][18][19]51,90,142]. Accordingly, we prioritized areas with a higher and increasing soil loss rate as SWC priority areas (Table 6).…”

“…Moreover, conservation priority levels were obtained to support the spatial planning and implementation of SWC measures in the study area. Prioritization was based on soil loss assessment results and change in erosion risk classes between 2000 and 2016 with the help of MCDR method [90][91][92]. We set the highest value for areas with a high and increasing risk of soil erosion.…”

“…The RUSLE model was run to estimate the soil loss rate for the year 2000 and 2016 separately. Erosion risk area was categorized into eight classes from very low to extremely high, following Uddin et al [90] for Koshi Basin. Classification of soil erosion risk area was based on the estimated rate of mean annual soil loss (Table 3).…”

Land Degradation by Soil Erosion in Nepal: A Review

“…About 21,000 m 3 of soil, equivalent to 64 t ha -1 , is being eroded annually in the Khajuri catchment of Siwalik Hills of Nepal [7]. In another soil erosion study undertaken in the Koshi basin of Nepal, soil loss of up to 22 t ha -1 year -1 in the barren lands were reported [10]. Mean soil loss rate of 11.17 t ha -1 year -1 was estimated in the Aringale Khola watershed of Nepal which indicated a major part of the watershed was degraded [11].…”