Based on hydraulic model test, overflowing capacity, water flow state, flow speed distribution, pressure, fluctuating pressure, downstream erosion of flood discharging tunnel and other parameters while total opening and part opening of No. 1 flood discharging tunnel of Hekoucun Reservoir have been observed. It is indicated in experimental study, water at the contraction section at the end of the sluice chamber gets fierce fluctuation, with spray reaching the tunnel top, and results in great negative pressure on the lateral walls on both ends of the contraction section in the original design scheme. After changing the shape of the transition, flow state has been improved, negative pressure reduced, so the design is adaptable; It is recommended in the test guiding plate can be added on the both sides of the cleaning door so as to reduce water-wing height; Three medium-size piers have been compared with the better pier recommended in the test.
