Modelling reservoir sedimentation management options

Petkovsek, G. and Roca, M. and Jourdain, C. (2024) Modelling reservoir sedimentation management options. In: River Flow 2024, 2-6 September 2024, Liverpool, UK. (Submitted)

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While dams serve many beneficial purposes, their construction brings various socio-environmental impacts. Some of those are related to interrupted flow of sediment downstream of the dam and sedimentation in the reservoir as well as upstream. To minimize these impacts, several sediment management approaches exist. The most suitable approach is to be selected based on the operational constraints and objectives of sediment management. Modelling the physical process of sedimentation in the reservoir, as well as upstream and downstream, can help in assessment of each approach and aid the selection process. In this paper, we describe the application of a sedimentation model to assess the upstream and downstream impacts, as well as impacts on the dam and reservoir itself, for the proposed 45 m tall Mpatamanga dam on the Shire River in Malawi. The model used is a long term one-dimensional model RESSASS, developed specifically for the purpose of reservoir sedimentation. It covers 22 km from the reservoir tail to the main dam, three tributaries, and the regulating reservoir and dam some 7 km downstream from the main dam. It is linked to the downstream model that covers several ecologically important areas, water intakes for irrigation, and another dam. Several scenarios were tested, exploring the impacts of different sediment inflow scenarios, to account for uncertainty in sediment yield estimations, and the impacts of different sediment management scenarios. The results show that all sand and most of finer sediment will deposit in the reservoir, causing erosion of existing sand deposits downstream. In absence of any sediment management strategy, after some 30 years there could be noticeable raise in bed and water levels upstream of the reservoir, mainly sand deposits, with impacts on the infrastructure, including power production of an upstream dam. Fine sediment deposits would reach the level of the bottom outlet, complexifying its safe operation. Management options considered include two main approaches: reduction of sand inflow on the main Shire River and tributaries, and operating at lower level during the wet period of the year to facilitate sand movement further into the reservoir. The model predicts that the water level drawdown scenarios are more efficient in mitigating the upstream impacts and improve releases from the reservoir, although sand is still not passing downstream in the first 30 years of operation.

Item Type: Conference or Workshop Item (Paper)
Subjects: Floods > Dams and reservoirs
Water > Water resources
Divisions: Floods
Depositing User: Helen Stevenson
Date Deposited: 15 May 2024 13:15
Last Modified: 15 May 2024 13:27

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