Effect of the barrage and embankments on flooding and channel avulsion case study Koshi River, Nepal

Effect of the barrage and embankments on flooding and channel avulsion case study Koshi River, Nepal

Devkota, L.
Crosato, A.
Giri, S.

Civil Engineering and Geosciences

Hydraulic Engineering

2012-12-31

Humans have utilized water resources for millennia by modifying natural river courses and such interventions have greatly influenced not only river flows and sediment fluxes, but also the overall river morphology. Situated in the Nepal's eastern Ganges region, the braided Koshi River is unique among the other rivers, because of the high frequency of channel avulsion and other morphological changes, such as: channel migration, channel width adjustment. This study examines effect of the Koshi barrage and related embankments on flooding and channel avulsion in Koshi River. In particular, it tries to explain the avulsion that occurred in 2008, studying the role of the Koshi barrage, and related embankments, constructed near the border between Nepal and India in 1963. Series of satellite images and historical maps show overall sedimentation, especially in the western side of the river channel, which lead to the shifting of the Koshi River towards the east (almost 6 km) during around 40 years period, since the construction of the barrage, although before, shifting toward the west. The barrage was constructed at eastern side of the river channel within two embankments, leading to sedimentation in western side, since river is flowing short courses. Sediment deposition upstream of the barrage brought to the conditions that lead to dike breaching in 2008. During the 2008 flooding event, huge amounts of previously deposited sediment were eroded from the river bed upstream of the barrage. The resulting bed lowering means a gain of time to prevent a similar event in the future, since new space for sediment inside the embankments system has been created. So, this time, estimated in 40-50 years, can be used to take proper river engineering measures.

aggradation, avulsion, barrage, flooding, Koshi River, morphology

http://resolver.tudelft.nl/uuid:b9026f10-e9b8-4cc6-9e27-93416804eac5

Society of Engineers' for Rural Development

Rural Infrastructure 3(3), 124-132. (2012)

Institutional Repository

journal article

(c) 2012 Devkota, L., Crosato, A., Giri, S.