RESERVOIR OPERATION AGAINST LARGE-SCALE FLOODS DUE TO TYPHOON HAGIBIS AND APPLICABILITY OF ENSEMBLE FORECAST TO PRELIMINARY RELEASE

Abstract

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