Using GIS, remote-sensing and linear modeling to prioritize spatially explicit action against erosion and sediment transport within Lake Victoria watershed in Kenya

Watershed degradation from human encroachment is a worldwide phenomenon and a keystone driver of erosion, transport and deposition of sediment material into downstream lakes and other water bodies. Despite global recognition of the growing scale of these linkages, comprehensive evaluation and ranking of the range of specific parameters associated catchment destruction and subsequent sediment movement, or those contributing to its mitigation, has rarely been undertaken. This study applied GIS with remote-sensing with linear modeling to assess influence of geomorphic and hydrological as well as land-use land-cover (LULC) elements in driving net erosion indicator (NEI), sediment transport indices (STI), and an index of overall erosion potential, ErPot combining NEI and STI. The LULCs were: crop cover, forest cover, wetland cover, urban-features cover while the geomorphic-hydrological parameters were slope gradient, elevation and sub-watershed size. This was undertaken across 10 delineated sub-watersheds forming the catchment of Lake Victoria on the Kenyan territory side. NEI was predicted to be enhanced by cop cover, urban development and slope angle; STI was enhanced by slope angle, sub-watershed upslope size. While ErPot increased with sub-watershed upslope size, NEI, STI and ErPot were all predicted to be mitigated by forest and wetland cover sizes. Using these results, the sub-watersheds of Busia-North, Rangwe and Homabay-North were considered priority for action to reduce net erosion indicator. Similarly, the Mara and Yala sub-catchments, and also the Mara the Yala and Nzoia sub-catchments were considered of greatest significance in prioritizing action to mitigate sediment transport and overall erosivity, respectively. These results, the first from modeling a trans-boundary freshwater catchment erosion, are practically applicable in decision making for designing a county-based strategy for habitat rehabilitation and conservation that specifically prioritizes the critical zones identified.