Technical Studies

Typhoon Morakot in 2009 brought an extreme flood with the peak near 35,000cms at Kao-ping Weir that exceeded the design flood (25,900cms), and resulted in severe fatalities and property damages. After typhoon Morakot, the meandering pattern of Kao-ping River changed and sediment concentration increasedsignificantlyy. To ensure the stable water supply of Kao-ping Weir, Southern Region Water Resources Office, WRA suggested four main strategies in 2012, namely stabilizing the flow path, improving the weir operation, enhancing flood protection level, and developing the alternate sources of water supply. In these strategies, the short-term measures including dredging channel regularly, setting up a diversion dike, and building embankment in Tashu, etc. were suggested. To ensure flood protection safety, however, some measures such as heightening the rubber and concrete weir which will increase the velocity near the intake could be excuted after the completion of short-term measures.

By analyzing basic data of Kao-ping Weir reach and simulating, this study further reviewed and assessed the short-term, mid-term, and long-term measures of stable water supply strategies. Therefore, a two dimensional mobile-bed model (CCHE2D) was adopted to simulate the tendency of channel migrationand deposition of Kao-ping weir reach. Additionally, by using three dimensional model (CCHE3D), the 3-D flow field near the diversion dike was simulated to demonstrate the improvement effect of the installation of diversion dike.

In the simulation of stable water supply plans, scenario 6.3 (heighten the base of rubber weir about 1 m, heighten the concrete weir to EL.18.5m, and setup the diversion dike located at the interface of the weir No.1 and concrete weir) was suggested. In comparison with the existing case, scenario 6.3 shows the velocity increases near the intake of Kao-ping weir, the bed elevation also has an erosion trend, and the flow path shifts toward the intake after the long-term simulation. Furthermore, according to the simulation results, the case combined scenario 6.3 with the dredging layout according the stable meander channel pattern proposed by Prof. Odgaard with the planning bed elevation could maintain a stable main channel and improve the water supply stability of Kao-ping Weir.