Influence of outlet discharge on the efficiency of turbidity current venting

Reservoirs created by dams are vital water infrastructures worldwide ensuring not only water, food and energy but also protecting against floods. Sedimentation endangers the sustainable use of these reservoirs. Fine sediments transported as suspension during floods into reservoirs normally represent the most important of the sediment yield. In deep and long reservoirs, the fine sediment laden inflow plunges and travels as a turbidity current along the bottom of the reservoirs downwards to the dam. Thus, during every inflowing flood event, a significant amount of fine sediments is transported by these turbidity currents directly to the dam. Besides the reduction of the useful storage volume, the water release structures as bottom outlets and intakes may be clogged by the fine sediments with time. When opening bottom outlets or low level outlets during the occurrence of turbidity currents, the latter may be vented through the dam before the deposition of the fine sediments in front of the dam. In practice, the question arises on how much sediments can be vented under a certain discharge capacity of the bottom outlet or low level outlet. By the help of systematic laboratory experiments in a flume and by numerical modeling, Dr. Sabine Chamoun studied for the first time the influence of outlet discharge on the efficiency of turbidity current venting. The effect of the reservoir bed slope as well as the dimensions of the bottom outlet were also highlighted. As another novelty, the timing of venting relatively to the arrival of the turbidity current at the dam and the required duration of venting were investigated. The systematic tests allowed also to quantify the efficiency of venting regarding the amount of sediments evacuated compared to the water used from the reservoir. Finally, Dr. Sabine Chamoun could give some practical recommendations on how turbidity current venting should be performed in order to attain the most optimum release of fine sediments for a certain outflow discharge.

Schleiss, Anton
Lausanne, EPFL-LCH

 Record created 2018-05-07, last modified 2019-01-24

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