Simulation of gravel transport in bypass tunnel during sediment bypass operation of Asahi Dam

Abstract

Sediment bypass tunnel is effective sediment countermeasure to reduce sediment inflow into the reservoir and supply sediment downstream of the dam. However, the gravel passing downstream while colliding in the bypass tunnel causes abrasion of the concrete inside the tunnel. Once the operation of the bypass facility is started, the investigation and repair of the abrasion inside the tunnel will be sustained. In order to maintain and manage the bypass tunnel over the long term, establishment of a method for predicting the abrasion area and the amount of wear in the tunnel by gravel is required. In this study, simulation of gravel passing through the tunnel was proposed to predict high frequency of abrasion area in the tunnel. Targeting the bypass tunnel of Asahi Dam in Japan, supercritical flow in the tunnel was analyzed using a three-dimensional flow model and using the calculation result of flow, particle tracking that can reproducing gravel behavior was simulated. Based on both simulation results and observations of tunnel abrasion, the influence of particle size on the migration path of gravel passing through the tunnel was investigated.