Combining connectivity modeling with remote sensing to elucidate flow and sediment connectivity of two adjacent subbasins in the Lake Tana Basin Ethiopia

Abstract

Sediment connectivity is the ability of a system to transfer water and sediment within a catchment. It is controlled by driving forces (rainfall and land cover), static aspects (geomorphology and soil), and dynamic aspects (surface runoff) of the catchment. The connectivity index is commonly used to measure sediment connectivity, even though it usually only looks at structural landscape features. The aims of this study are 1) to assess flow and sediment connectivity using the Borselli's index (IC) and the modified index of connectivity (MIC) and 2) to compare flow and sediment connectivity between two catchments in the Lake Tana Basin. The modified connectivity index was calculated by adding soil erodibility, rainfall erosivity, roughness index, and surface runoff. Remote sensing data were used to estimate the driving forces of connectivity, structural aspects of connectivity, and also functional aspects of connectivity. Landsat 8 OLI was used to identify the land cover, and remotely sensed rainfall estimates (TAMSAT) were used to quantify the precipitation in the catchments, while the Shuttle Radar Topographic Mission (SRTM) was used to identify slope gradient and roughness index. The IC values were higher than the MIC values, whereas the MIC values have a wider range of values compared to the IC values. The MIC can represent functional connectivity within the catchment. The IC and MIC values in the Gumara were higher than those in the Rib.