Effects of dam construction on the Ribb River bed topography

Abstract (2017)

Authors

C.A. Mulatu IHE Delft Institute for Water Education, Bahir Dar University
A. Crosato IHE Delft Institute for Water Education, Environmental Fluid Mechanics - CEG
Research Group
Environmental Fluid Mechanics (CEG) (TU Delft)
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Published Date

2017

Language

English

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Faculty

Civil Engineering & Geosciences

Department

Hydraulic Engineering

Research Group

Environmental Fluid Mechanics

Abstract

Dam
construction affects the discharge regime and the sediment transport of rivers
(e. g. Williams & Wolman, 1984). Dams reduce the annual peak discharges
(Graf, 2006) and may store all sediment or a large part of it. The downstream
river reach adjusts its morphology to the new conditions. This involves changes
in planform, slope, width, depth and sediment characteristics through time. The
Ribb River is located in the North Western part of Ethiopia where it drains to
Lake Tana. A 73 m high dam and a diversion weir 30 km downstream are under
construction to irrigate 15,000 ha of land (WWDSE & TAHAL, 2007). The river
reach downstream of the dam is 77 km long. This part of the river is strongly
affected by flooding, pump irrigation, sand mining and backwater effects from
Lake Tana and will be even more impacted by Ribb Dam operations. Lake Tana
level was regulated for hydropower production at a higher elevation between the
years 1995 and 2001, at a lower elevation between the years 2001 and 2010 and
then to a higher elevation again. Embankments have been constructed in the lower
part of the river for flood prevention. The objective of this study is to
analyse the effects of the dam on downstream river bed topography and channel
alignment. This work presents the assessment of pre-dam morphological trends of
the river.