RESERVOIR OPERATION AGAINST FLOODS DUE TO TYPHOON HAGIBIS AND APPLICABILITY OF ENSEMBLE FORECAST TO PRIOR RELEASE

Abstract

 Recordable heavy rainfall hit and caused severe floods in a wide area in the eastern Japan due to Typhoon Hagibis in October, 2019. This paper aims at clarifying an effective way to manage large-scale floods by reservoirs by analyzing reservoir flood control practices during this flood event. The paper firstly reviews flood control of reservoirs in this event to discuss effectiveness and issues of current reservoir operation practices. An detailed analysis is then carried out to estimate effects of flood control by two reservoirs in the Sagami River basin, where one of reservoirs conducted the emergency spillway gate operation due to extremely large-scale rainfall. The paper also investigates applicability of a medium-term operational ensemble rainfall forecast to prior release of reservoirs for enhanced management of large-scale floods.