TWO-DIMENSIONAL HYDRODYNAMIC MODELLING OF URBAN FLOOD INUNDATION CAUSED BY THE SOUTHWEST MONSOON TO CHARACTERIZE THE IMPACT OF TWENTY-YEAR DIFFERENCE IN LAND USE IN VALENZUELA-OBANDO-MEYCAUAYAN (VOM) USING FLO-2D

Abstract. The intensity of urban flooding area due to rapid urbanization in Metro Manila has been worsening over the years caused by the torrential rains brought by the Southwest Monsoon. To further characterize the impact of land use change influenced by urbanization, we compared the flood map generated from two periods (Year 200 & Year 2020) using a two-dimensional hydrodynamic modelling simulated in FLO-2D software. In our simulations, we assigned roughness coefficient values to corresponding land use category derived from an earlier study in the area previously spearhead by JICA in 2001. Each model will incorporate the implemented Year 2000 land use and the projected Year 2010 land use classification respectively, which were used in this earlier study. Meanwhile, both models will use the same sets of parameters for the simulation: IFSAR-derived DEM elevation model and a rainfall event with 10-yr return period. The area of interest of this study is located near Valenzuela-Obando-Meycauayan (VOM) with its boundaries defined from the National Mapping and Resource Information Authority. The flood simulations conducted do not take into consideration in existing flood control measures such as drainage systems and floodwalls to minimize the complexity of the model. The results are evaluated both quantitatively and qualitatively. According to the results, the impact of the land use change on flood formation in most areas are insignificant due to a low degree of land use change. However, there has been substantial impact on flooding in specific areas where there is a major change in the land use. For further studies, we recommend the use of a longer land use change period and the consideration of more varied and precise Manning’s n-values.