Page - 542 - in Book of Full Papers - Symposium Hydro Engineering

is smooth and no waves were observed in the MP. During a high flow condition, discharge starting power shutdown Q=800㎥/s, the flow pattern shows oscillations due to the forming of a vortex in front of the bypass tunnel inlet. The water level in the modified pool is kept at operation reservoir level(765m a.s.l) for NPO and high flow condition. Flow velocities are measured with an Acoustic-Doppler-Velocimetry probe(ADV). During NPO, flow velocities only exceed 0.2m/s in the region of the cofferdam and close to the power intake. In a large region of the MP the vertical velocity fluctuations are smaller than the settling velocity of 2.5㎝/s for grains with d=0.2㎜ in still water. Therefore, larger grains are expected to settle in the MP during power operation. Fig 8. Top View on the Modified Pool for Q=156㎥/s(left) and 800㎥/s(right) Second, a transfer experiment of suspended sediments was conducted for HQ5-A load case, maximum discharge was 748.6m3/s, to identify deposition properties of fine sediment. The following table (Table 8) gives an overview of the deposited and sluiced sediment volumes measured in the model. These results show that all inflow sediment targeted diameters (above 0.2 ㎜) are deposited through the bypass tunnel and modified pool. Table 6. Sediment Balance Parameter (HQ5-A) Bed load Suspended load Quantity (㎥) Ratio (%) Quantity (㎥) Ratio (%) Previous depositions 40,000 150,000 Inflow added to the inflow 2,750 100 68,000 100 Deposit Upper coffer dam 2,750 100 49,220 72 modified pool - 11,200 16.5 Sluiced through the bypass tunnel 500 7,580 10.9 Power intake 400 0.6 Finally, we conducted a reservoir flushing test to find the optimum condition to remove deposited sediments. The performance of the two flushing tests (Q = 542