Assesment of Riverbed Change Due to the Operation of a Series of Gates in a Natural River

Changes in the bed of Geum River (L=130 km from Daechung regulation dam to Geum River estuarial bank) in South Korea were predicted using the 1-D HEC-RAS model and the 2-D CCHE2D model. Three movable weirs have been installed and dredging has been carried out in Geum River under the Four Major Rivers Restoration Project (2009-2012). Inflow data of sub basins were calibrated with daily runoff data generated by PRMS based on a hydrologic unit map. To determine the gate opening height for maintaining the management water level, unsteady analysis was performed using HEC-RAS. Thereafter, long-term riverbed changes through quasi-unsteady analysis were simulated for 20 years. In order to investigate the effect of movable weirs, sediment analysis was done for three cases of gate opening: case 1 is fully close, case 2 is fully open, and case 3 is regulating gates by the operating rule. Also, short-term riverbed changes were predicted with CCHE2D for 11 days in the problem area, depending on the results of 1-D model, and the effect of dikes was examined. In future, gate operation and structural methods such as dikes must be in step with each other in order to manage sediment and rivers in an ecofriendly manner