[A-CG37] Water and Sediment Dynamics from Land to Oceans [En]

[ACG37-01] Urban fluvial and pluvial flood modeling for integrated flood risk assessment

★Invited Papers

*Tomohiro Tanaka¹ (1.Kyoto University)

Keywords:Urban Flood Modeling, Pluvial and Fluvial Flooding, River Bathymetry Data

An increasing urban pluvial and fluvial flood risk encourages deeper understanding and efficient numerical modeling of flood dynamics and associated social impacts. The author has been developing an integrated catchment-scale rainfall-runoff and regional-scale inundation model and testing it in various case studies in Japan and Asian countries. This presentation will deliver significant advancement of regional flood modeling from several case studies by the author. The first case study will focus on Nagoya where a severe rainfall event in 2000 caused both fluvial and pluvial flood damage. The interactive fluvial and pluvial flood model by combining rainfall-runoff, inundation and sewage model components overall reproduced severe flood extents. The constructed model is input with a large ensemble climate simulation data and provides fluvial and pluvial flood risk curves for social impact assessment. The results indicated that pluvial flooding presents comparable economic risk to fluvial flooding (16% and 17% lesser damage at 50- and 100-year return periods, respectively) despite its significantly shallower flood depths (area with flood depth over 45 cm was only 10.5% and 5.4%, respectively). This is because pluvial floods widely occur over the city, including areas further away from the river. Furthermore, probably similar with other mega cities with long history, fluvial flood risk has been managed by settling the central economic district (originally the Nagoya Castle founded several centuries ago) on higher altitudes. Another type of case study in urban flood modeling will focus on fluvial flood modeling without local river bathymetry data, using digital elevation model (DEM) instead. High resolution DEM provides useful alternative information for river bathymetry. Two case studies of utilizing 1-m and 5-m DEM are presented in which the river and inundation model exhibit reasonable performance. The results indicated appropriate elevation data for river bathymetry modeling depending on the spatial scale of target rivers. Throughout the case studies, the author hopes to introduce the recent advancement of regional flood modeling and to discuss a way forward.