UAV-Based Floodwater-Level Establishment for FEWS for Abrupt River Section Change in Imsan

Flood damage has been increasing owing to climate change; thus, a flood early-warning system (FEWS) has been established to evacuate residents safely in flood-prone areas. The FEWS is a fundamental nonstructural system that reduces human and material damage caused by floods. The damage can be minimized when appropriate settings are used. In general, the need for an early warning is determined using a water gauge installed on a bridge. If there is an abrupt change in the river section near the bridge, an alarm is issued based on the water-level gauge on the bridge. However, some areas may be more vulnerable to flooding than where the bridges exist. In these cases, vulnerable areas can be inundated by floods before a warning alarm is provided. The current study area of the Chogang-cheon River is such an area. Therefore, an unmanned aerial vehicle (UAV)-based remedy is proposed to overcome the discrepancy between the flooding water levels of the gauge location and the vulnerable area. First, spatial information about the river cross section was obtained through a UAV for the study area. As a result of Pix4D processing after river surveying by the UAV, a noticeable abrupt river width change section was confirmed, particularly upstream of the Gwangi Bridge in the middle of the Chogang-cheon River. Then, the level of the bridge and the upstream point of the bridge for the same flow rate were calculated using the Hydrologic Engineering Center River Analysis System (HEC-RAS) program. Through this remedy, the section of the river where flooding occurs first was defined, and an appropriate flood early-warning water level was appropriately estimated. The approach in this study can be widely applied to rivers where a FEWS is needed to determine where rivers change abruptly.