The downstream section of Dajia River had a constant headcut scour, which threatened the structural safety of Shih-Gang Dam. Therefore, the river management office proposed a plan to stabilize the riverbed and install an energy dissipator in the river. The results of a hydraulic model test revealed a reduction in the average flow velocity at the location of the energy dissipator under different scenarios. At a 5-year frequency peak flow rate (Q5 = 3800 cms),the velocity decreased from 11.1 to 6.6 m/s (−40.5%), and at a 100-year frequency peak flow rate (Q100 = 8800 cms),the velocity decreased from 13.3 to 9.5 m/s (−28.6%). In front of the Pifeng Bridge, at the 5-year frequency peak flow
rate (Q5 = 3800 cms), the average flow velocity decreased from 11.9 to 8.1 m/s (−31.9%); at the 100-year frequency
peak flow rate (Q100 = 8800 cms), it decreased from 13.8 to 12 m/s (−13%). The estimated energy dissipation in the
river due to hydraulic jump was 4.74 m (1.8%); at the location of the energy dissipator, the energy dissipation due to hydraulic jump increased to between 11.65 to 12.55 m (4.5% to 4.7%). On the basis of these results, we concluded that the energy dissipator effectively dissipated the downstream energy, which may help to reduce scouring.
Key Words: Dajia River, Riverbed Stability, Shih-Gang Dam