Detections of Infrasound Waves From Water Discharges at a Hydroelectric Dam: Implementation of Timely Warnings for Unexpected Discharge Events

Water discharges at hydroelectric dams on the Imjin River, which flows through North and South Korea, generate abrupt water level increases downstream. We assessed infrasound signals from water discharges using an infrasound array located similar to 32 km from the source and applied infrasound detection in a flash flood alert system. Using infrasound signals, there was a 79% detection rate for 48 water level increase events occurring in the river downstream during a 14-year period (2008-2021). The detected signals had a low amplitude, long duration, and broad frequency range (0.5-15 Hz). The energy curves of the detected infrasound signals for selected events showed good correlations with the onset times and water level variations in water level records. These results demonstrate that infrasound monitoring can serve as a practical early warning system for impending flash floods resulting from unnoticed water discharges or sudden debris flows in mountainous regions. Plain Language Summary Infrasound waves are low-frequency atmospheric acoustic waves that travel long distances due to low energy loss. Infrasound can be generated from various natural and anthropogenic phenomena. Water dam discharges and waterfalls produce infrasound waves in the atmosphere by converting the potential energy of the massive amount of water to acoustic energy during the collision of water masses at the water pool. We analyzed infrasound signals from water dam discharge events and found that low-amplitude coherent signals could be detected and recorded as characteristic signals at a remote infrasound sensor array. The infrasound detection parameters can be correlated with water level rise onset times and variations recorded downstream. Similar to earthquake early warning systems, infrasound monitoring can be used to provide prompt alerts of flash floods resulting from unexpected dam discharges or substantial debris flows in mountainous regions, which would enhance civil protection in riverside downstream areas.