A simple DEM assessment procedure for gully system analysis in the Lake Manyara area, northern Tanzania

Abstract

Gully erosion is a major threat concerning landscape degradation in large areas along the northern Tanzanian Rift valley. It is the dominant erosion process producing large parts of the sediments that are effectively conducted into the river network. The study area is located in the Lake Manyara-Makuyuni River catchment, Arusha, northern Tanzania. During fieldwork, we measured topographic data of eight gully systems close to Makuyuni Town. The main focus of this study is to assess gully erosion dynamics using improved DEMs with original resolutions of 30 and 20 m, respectively. We assessed terrain characteristics to extract information on environmental drivers. To improve the DEM, we integrated information deduced from satellite images as well as from acquired GPS field data. Topographic indices such as Stream Power Index or Transport Capacity Index were derived from the re-interpolated DEM. To evaluate gully evolution, we assessed also the longitudinal slope profiles. Finally, the gully evolution phases of each gully were classified according to the concept proposed by Kosov et al. (Eksperimental'naya geomorfologiya, vol 3. Moscow University, Moskva, pp 113-140, 1978). The reinterpolated DEMs revealed a positive response especially for the more developed gullies. We show that the extraction of information on this spatial process scale based on ''lowresolution'' data is feasible with little additional fieldwork and image interpretation. In fact, areas identified as having a greater risk of gully erosion have been confirmed by observations and surveys carried out in the field.

Erosion Gully Networks Extraction Based on InSAR Refined Digital Elevation Model and Relative Elevation Algorithm—A Case Study in Huangfuchuan Basin, Northern Loess Plateau, China

“…In contrast, the reference ASTER DEM with a coarser resolution (30 m) achieved an F1 score of 72.17%. Thus, our study confirmed that it is feasible to extract gullies from lower-resolution DEMs by employing suitable information enhancement methods, as suggested by Maerker et al [71].…”

Soil erosion and sediment transport in Tanzania: Part II – sedimentological evidence of phased land degradation

“…While the amount of grazing land has decreased, the number of livestock in the area has, like the rest of Tanzania, doubled in the same period, seriously increasing livestock densities and grazing pressures (FAO, 2019). The combination of these land-use changes with a natural high vulnerability to soil erosion has resulted in a marked increase in surface erosion, gully incision and land degradation in the area (Blake et al, 2018;Kiunsi & Meadows, 2006;Maerker et al, 2015). The combination of land degradation by erosion and siltation of the water bodies threatens ecosystem health and service provision in the region (Janssens de Bisthoven et al, 2020).…”

Soil erosion and sediment transport in Tanzania: Part I – sediment source tracing in three neighbouring river catchments

“…Smaller pockets of forest and wetland vegetation are confined to the uplands and floodplains, respectively. However, a combination of unsustainable land-cover changes and a natural high vulnerability to soil erosion resulted in a marked increase in surface erosion, gully incision and land degradation in the area (Blake et al, 2018b;Kiunsi & Meadows, 2006;Maerker et al, 2015;Wynants et al, 2018). Therefore, three sub-catchments (Figure 1 and Table 1) were selected for a detailed investigation into the sources of transported sediment: Nanja, weathered soils, medium to steep slopes and variable rainfall levels.…”