Hydraulic Analysis of the Marikina River Floodplain During Typhoon Vamco using Numerical Modelling

Typhoon Vamco in 2020 costed the Philippines over PHP 19 billion in damages. One of the heavily affected floodplains is the Marikina River floodplain. Discharges of up to 2582 m3 s−1 along Marikina River were noted. This is the strongest flashflood incident in the area after Typhoon Ketsana in 2009. This study aims to investigate the hydraulics of flood development within the Marikina River floodplain during Typhoon Vamco using numerical modeling. The hydraulic model in HEC-RAS utilized a 1 m LIDAR DTM, calibrated discharges from a hydrologic model and water levels as upstream and downstream boundary conditions, respectively, and a rain-on-grid input. Results showed a max inundation area of ∼ 75 km2 and flood depths of up to 4 m which accounts for the damages in some municipalities and cities in Metro Manila and Rizal Province. Model validation showed the simulated peak level (11.31 m a.s.l.) to be only 1.0 % lower than the peak observed water level (11.43 m a.s.l.). Model results can be used for measures to minimize risk and damages.