Morphodynamic Trends of the Ribb River, Ethiopia, Prior to Dam Construction

Geosciences (Switzerland) - Tập 8 Số 7 - Trang 255
Chalachew Abebe Mulatu1,2,3, Alessandra Crosato1,3, Michael M. Moges2, Eddy J. Langendoen4, Michael E. McClain1,3
1Faculty of Civil Engineering and Geosciences, Delft University of Technology, 2600 GA Delft, The Netherlands
2Faculty of Civil and Water Resources Engineering, Bahir Dar University, P.O. Box 26, Bahir Dar, Ethiopia
3IHE Delft, Department of Water Science and Engineering, 2601 DA Delft, The Netherlands
4U.S. Department of Agriculture, Agricultural Research Service, Watershed Physical Processes Research Unit, Oxford, MS 38655, USA

Tóm tắt

The meandering Ribb River flows in northwest Ethiopia to Lake Tana, the source of the Blue Nile River. The river has already undergone changes due to several human interventions, such as embanking, sand mining, water extraction and lake level regulation for hydropower. At present, a dam and a weir are under construction to store and divert water for irrigation. This will strongly alter both water and sediment discharges to the downstream river reaches, causing adjustments to the morphology. Assessing the current morphodynamic trends is the first necessary step to study the future effects and find ways to mitigate them. This paper presents an analysis of the current and past river based on newly collected data, aerial photographs, SPOT and Google Earth images. The riverbed changes are derived from historical staff gauge height analysis. The effects of sediment mining and water extraction are assessed using the theory of morphodynamic equilibrium. The findings of the analysis show a reduction of sediment transport capacity in the downstream direction, which has resulted in intense sediment deposition, resulting in blockage of the Lower River reach and subsequent channel avulsion. The effects of Lake Tana level regulation on the observed processes appear to be minor.

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Geosciences (Switzerland)

Tập 8 Số 7

255

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