[A-HW20] Integrated Watershed Management under the Future Extreme Disaster

[AHW20-P02] Enhancing Desilting Effectiveness for Long-Term Risk Assessment in Reservoir Storage with Diverse Countermeasures

Jihn-Sung Lai², Cheng-Chi Liu², *Fong-Zuo Lee¹, Pei-Te Chiueh² (1.National Chung Hsing University, 2.National Taiwan University)

Keywords:reservoir storage, desilting operation, long-term risk, numerical model, risk analysis

Zengwen Reservoir, the largest reservoir in Taiwan by volume with a designed capacity exceeding 740 million cubic meters, faces challenges due to excessive rainfall in its catchment area. Extreme weather leads to soil erosion during the rainy and typhoon seasons, resulting in a significant volume of sediment streaming into the reservoir. Consequently, it experiences high-concentration turbid water or density currents, causing a rapid increase in suspended solids concentration in front of the dam. The long-term inflow of sediment and bed deposition have led to a decline in Zengwen Reservoir's capacity by approximately 200 million cubic meters. Despite this, the reservoir must remain connected to Wushantou Reservoir to serve as the primary water source for the Jianan irrigation system, fulfilling the demand of water supply.
For long-term risk assessment in reservoir storage, this study involves several steps to evaluate the efficiency of desilting operations. First, it collects data on reservoir terrain, historical hydrographs, and records of gate operations. Next, it builds a reservoir model using a two-dimensional numerical model of Zengwen Reservoir. The study then analyzes sediment transport behavior and the venting efficiency of desilting operations during flood events of different return periods, typhoons, and heavy rain. Based on the data collected and simulated results, the study estimates the reservoir capacity and future water supply of Zengwen Reservoir. It develops a risk analysis method to assess the effectiveness of long-term risk mitigation in reservoir storage with various countermeasures. The findings of this study can serve as a reference for reservoir management agencies involved in flood control and desilting operations. Furthermore, the results are expected to inform related research endeavors in the pursuit of sustainable reservoir management objectives in the future.