Assessing Irrigation Water Capacity of Land Use Change in a Data-Scarce Watershed of Korea

The objective of this study is to assess stable irrigation water capacity and erosion on the basis of water and sediment balance analysis of land use change. The reservoir water balance analysis is calculated by the daily irrigation reservoir operation model (DIROM) for simulating daily inflow and release rates for irrigation reservoirs. The reservoir capacity change for assessing the sediment flux is predicted using the universal soil loss equation (USLE), sediment delivery ratio (SDR), and trap efficiency. To analyze soil erosion changes according to land use changes, Landsat-5 images were selected. Spatial distribution of deposited sediment is estimated by the U.S. Bureau of Reclamation (USBR) method and the hydrodynamic, sediment and contaminant transport model (HSCTM-2D), which is a finite-element model for simulating surface water flow and sediment transport. The model performance was verified by comparing simulated and observed data. The simulated results, which were validated using an internal mass balance method because of the scarce observed data, showed that the soil erosion of the Lake Asan watershed has increased at a rate of 2% per year from 1986 to 2000, and the storage capacity after 50 years will decrease by 65% without proper sediment conservation implementation. It is necessary to maintain stable irrigation water capacity by appropriate management of reservoir rehabilitation. The annual dredge amount was determined by various dredge scenarios according to the sediment removal volumes using frequency analysis. This approach will be useful for managers to identify the location and amount in which sediment dredging would be best for stable irrigation water supply maintenance.