Analyzing gully erosion in the Lake Manyara catchment– Tanzania

Abstract

Despite being mentioned as an important land degradation process in the Lake Manyara catchment in Tanzania, little is known about the role of gully erosion in Lake Manyara catchment. Lake Manyara is a basin with no outflow making it vulnerable to local sediment dynamics. The biodiversity is high and the national park that is located in the Lake Manyara catchment is an important source of income for the region. A combination of fieldwork and modeling with SWAT was implemented to study gully erosion in the catchment. The fieldwork measurements consisted of the inserting erosion pins in and around the gully heads and channels of two different gully systems and measuring the growth. Additionally, SWAT was used to model the surface runoff and sediment yield that is transported into one of the two studied gully systems. Further, SWAT was also implemented to study a scenario in which the agricultural land cover in the area is increased. The measured sediment mobilization ranged from 0.01 to 1.71 m3 per month. In the modeled catchment an average sediment yield which ranged from 4.5 to 15.7 t/ha/yr was found. For the scenario with increased agricultural land cover, the sediment yield increased significantly. The exact amount of sediment that ends up in the lake is unknown, but the current study provides an indication of the magnitude of sediment erosion in the catchment.