Design concepts of desilting tunnel at Shimen Reservoir in Taiwan

Abstract

In northern Taiwan, Shimen Reservoir is the main water conservation facility, which has the function of irrigation, electric power generation, water supply, flood prevention and tourism (Figure 1). Through 53 years of operation, the most challenging issue of the reservoir is severe siltation. The capacity of the water conservation is decreasing and 20% of the effective storage volume was lost due to siltation. Furthermore, the frequency of heavy rainfall has increased due to global climate change, so it has become imperative to develop measures to enhance silt-sluicing and flood-discharging capabilities of the reservoir. Accordingly, Water Resources Agency (WRA) planned to build a desilting tunnel, whose intake structure is situated at Amuping area, 7 km upstream from the dam. After completion, the tunnel could carry silt as well as coarse and fine sand outward to the outlet structure. The desilting tunnel is expected to deal with 6.4 × 105 m3 silt per year and increase 600 m3/s flood-discharging capability as well.