VARIATION IN EVACUATION TRIGGER RIVER WATER LEVELS BY DIFFERENT DEPARTURE POINTS IN A FLOODPLAIN

Abstract

 In flood evacuation using My Timeline, residents themselves determine in advance the criteria for starting evacuation (when evacuation should begin). However, a systematic method for determining the criteria personalized for individual residents has not yet been developed. In this study, under conditions where river water level is used as evacuation trigger, we calculated the maximum water level at which evacuation succeeds (maximum evacuable water level) for each departure point using five rainfall scenarios with different return periods on the floodplain of Serikawa River in Shiga Prefecture. The results show that the relationship between magnitude of rainfall and maximum evacuable water level varies depending on the floodplain type. In area affected by main river flooding, maximum evacuable water level is lower for the 100-year and 200-year rainfall event. Conversely, in area affected by only inland flooding, maximum evacuable water level is lower for the 10-year rainfall event. These differences are attributed to factors such as rainfall patterns and land use/microtopography around the departure points, which can significantly impact the critical evacuation water level.