A proposal of unit watershed for water management based on the interaction of surface water and groundwater

In South Korea, 850 standard watersheds and 7,807 KRF catchment areas have been used as basic maps for water resources policy establishment, however it becomes necessary to set up new standard maps with a more appropriate scale for the integrated managements of surface water-groundwater as well as water quantity-quality in the era of integrated water management. Since groundwater has a slow flow velocity and also has 3-D flow properties compared to surface water, the sub-catchment size is more effective than the regional watershed for the evaluation of surface water-groundwater interaction. The KRF catchment area, which has averagely a smaller area than the standard watershed, is similar to the sub-catchment area that generally includes the first-order or second-order tributaries. Some KRF catchment areas, which are based on the surface reach, are too small or large in a wide plain or high mountain area. Therefore, it is necessary to revise the existing KRF area if being used as a unit area for integrated management of surface-water and groundwater. A unit watershed with a KRF area of about 5 to 15 km2 can be effective as a basic unit for water management of local government considering a tributary composition and the location of groundwater wells, and as well it can be used as a basic tool for water demand-supply evaluation, hydrological observation system establishment, judgment of groundwater permission through a total quantity management system, pollution assessment, and prioritizing water policy, and etc.