The authors have been conducting a study to determine key monitoring points during heavy rainfall in terms of developing a business continuity plan in the event of a disaster as well as developing a highway disaster prevention plan. Through the study, it has been recognized that it is important to visualize where rainwater will gather in order to efficiently identify the monitoring points during the period of heavy rainfall. However, traditional catchment area analyses are not suitable for examining where rainwater accumulates. This is because with this method, only flow paths having a large flow rate tend to be emphasized if the catchment areas are relatively small and have small water catchment capacity, such as highway slopes or areas near the tunnel entrance. Therefore, a method to capture all possible flow paths during a heavy rainfall have been newly developed by first distributing raindrops uniformly on a digital elevation model, tracking the path of the raindrops, and then drawing flow lines. This method enables to identify the area, potentially affecting the earth structures of the highways due to localized rainwater during a severe rainfall.

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