Runoff and Sediment Monitoring in an Agricultural Watershed in the Ethiopian Highlands
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Citation
Ingrid Zehetbauer. (28/2/2014). Runoff and Sediment Monitoring in an Agricultural Watershed in the Ethiopian Highlands. Vienna, Austria: University of Natural Resources and Life Sciences, Center for Development Research (BOKU - CDR).
Abstract
This master thesis was conducted in the Gumara-Maksegnit watershed, which covers an
area of 54 km² and is located in the Lake Tana basin in the North West Amhara region,
Ethiopia. This region is affected by severe land degradation due to soil erosion. Heavy and
intense rainfall events during the rainy season between June and September lead to
formation of gullies and loss of fertile top soil. The knowledge of local runoff and sediment
yield is important as a basis for regional soil conservation planning.
This study provides runoff and soil loss data on watershed and sub-watershed scale of the
rainy season 2012. In order to achieve this goal, discharge and suspended sediment
concentration was measured at channel gauging stations at the main outlet of the Gumara-
Maksegnit watershed and two smaller sub-catchments within the watershed between 26th of
June and 4th of September 2012. One sub-catchment called Ayaye (24 ha) is treated with soil
conservation measures, whereas the other sub-catchment Aba-Kaloye (34 ha) remains
untreated. Sensors were installed at the channel gauging stations, which made a continuous
measurement of water level and suspended sediment concentration possible. While a rating
curve had to be derived for the main outlet to achieve the relationship of water level and
discharge at the fixed cross-section, at the two sub-catchments outlets this dependency is
already given due to the geometry of installed measuring weirs.
Measuring difficulties led to missing information and to only few days with existing data of all
sensors at each outlet. For a ten days period, in which all sensors worked continuous
measurements were possible, related to the watershed’s area the total soil loss amounted
8.31 t ha-1 in Gumara-Maksegnit watershed for this observed time period. Taking into
account that the rainy season lasted about nine times longer the severity of the problem
becomes obvious.
Additionally, major uncertainties in the monitoring setup could be revealed and a list of
suggested measures was generated to make future monitoring more effective