Optimal distribution of groundwater monitoring wells near the river barrages of the 4MRRP using a numerical model and topographic analysis

The aim of the Four Major Rivers Restoration Project (4MRRP) was to mitigate flood damage by controlling surface water levels via the construction of large barrages along the main rivers of South Korea. The increase in surface water levels behind such barrages can lead to a rise in groundwater levels upstream, which may increase the likelihood of flooding after heavy rainfall or during non-pumping periods. A total of 900 groundwater monitoring sites, comprising 446 automatic and 454 manual stations, are proposed on the low-lying plains alongside the rivers based upon the following criteria: groundwater flow directions, topography (determined using GIS analysis), the desire for equal spacing of monitoring wells, economic efficiency, field accessibility, and cost. A numerical model (MODFLOW) is used to estimate future groundwater flow directions and the area likely to be affected by a rise in surface water levels after barrage construction. Since 2011, 137 automatic monitoring wells have been constructed, and recent time series data show that groundwater levels are closely linked to surface water levels, and increased rapidly for the first 1–2 years after barrage construction. Groundwater monitoring wells will be essential for assessing the depth to groundwater, forecasting the extent of any potential flooding, and developing countermeasures such as drainage system.