Application of two-dimensional layer-averaged model on sediment flux assessment under an artificial countermeasure

Effective sediment management in reservoirs is essential for sustaining storage capacity, with sediment transport significantly influencing bed topography. This study applies a two-dimensional layer-averaged model (2DLAM) to assess sediment flux under a dredged guiding channel (DGC) in Zengwen Reservoir, Taiwan. The DGC directs inflow sediment toward outlet facilities near the dam. Topographic and hydrological data were used to calibrate the model and compare sediment flux with and without the DGC. The sediment transport and bed erosion-deposition trends within the reservoir are analyzed through quantitative flow simulation. The simulation results contribute to assessing the optimal DGC location and establishing a 2DLAM for a reservoir with the DGC topography. The DGC in the Zengwen Reservoir extends from the inlet of the desilting tunnel in front of the dam to the upstream section A-19, with a longitudinal distance of approximately 11,990 meters and a slope of 0.00365. The bottom width of the main deep channel is 200 meters, with an average depth of 7.92 meters. Simulations with and without the DGC were conducted using 2DLAM under various flood return periods (Q2, Q5, Q10, Q20, Q50, Q100, Q200) to evaluate sediment flux at each outlet facility. The simulated results show that the DGC significantly influences sediment discharge through the spillway and desilting tunnel. Compared to the scenario without the DGC, the average desilting efficiency of spillway increases from 6.22% to 8.68%, while that of the desilting tunnel increases from 10.12% to 13.95%. Overall, implementing an artificial countermeasure such as the dredged guiding channel in the Zengwen Reservoir can effectively guide the inflow sediment toward the inlet of desilting tunnel, thus enhancing the sediment flux at the desilting tunnel. When the peak flow is higher, part of the sediment can be diverted to the inlet of the spillway for sediment discharge.