In this study, the effects of sediment supply on the downstream of a large dam are investigated using a numerical model. The model simulation shows a good agreement with laboratory experiment results of sediment transport and diffusion from sediment pulses. The water surface changes from the various sediment bed elevations are also simulated using the model. The site which has a relatively stiff bed slope and meandering of a channel is selected as an appropriate location for sediment supply because of its shear stress enough to supply the sediment downstream. The model simulation shows the decrease of channel bed elevation through the simulation period with time. The well-deposition of sediment supplied from the downstream of dam is found in the location where the flow rate is relatively low. A bed relief index is increased with time and it is relatively greater in downstream compared to upstream. The channel bed variability increases as flow rate increases with a greater bed relief index. The results of this study demonstrate the importance of increasing water discharge of a large dam to increase the dynamic of channel bed and thus to enhance the efficiency of channel bed restoration by sediment supply.

In this study, Hydrologic regime alterations(magnitude, magnitude and duration of annual extreme, frequency and duration of high and low pulse, rate and frequency of water condition changes, Range of Variability Approach) were analyzed by using Indicators of Hydrologic Alterations at the 11 major multi-purpose dam. The analysis result of the magnitude of monthly water conditions during drought season, inflow was 6.38 ㎥/sec ～ 39.84 ㎥/sec and outflow was 20.36 ㎥/sec ～ 49.43 ㎥/sec, was increased 1.84 % ～ 200.98 %. The analysis result of the magnitude of monthly water conditions during flood season, inflow was from 79.06 ㎥/sec to 137.12 ㎥/sec and outflow was from 65.32 ㎥/sec to 80.16 ㎥/sec, was decreased from 18.19 % to 40.39 %. The analysis result of the magnitude and duration of annual extreme, 1-day minimum was increased 82.86 % ～ 2,950 %, but 1-day maximum was decreased 34.78 % ～ 83.96 %. The analysis result of the frequency and duration of high and low pulse, low pulse count was decreased 29.67 % ～ 99.07 % and high pulse count was also decreased 4.60 % ～ 92.35 % after dam operation. Hydrograph rise rate was decreased 15.84 % ～ 79.31 % and fall rate was 1.97 % ～ 107.10 %. RVA of 1-day minimum was increased 0.60 ～ 2.67, also RVA of 1-day maximum was decreased 0.50 ～ 1.00.