FLOOD INUNDATION MAPPING ALONG THE PROPOSED DIKE SYSTEM OF THE CAGAYAN DE ORO RIVER: THE SENDONG SCALE FLOOD

摘要

In recent years, Cagayan de Oro has experienced the damaging impacts of flooding. In December 2011, Tropical Storm Sendong (Washi) caused the most devastating flood in the city's history which caused unparalleled damages and casualties. To mitigate the impacts of river flooding, the DPWH has instituted the Flood Risk Management Project - Cagayan de Oro River which proposes the construction of a 12-km dike system along the river. However, the dike system is designed for a Pablo scale flood which is estimated at 25-year return period, as compared to a Sendong scale flood which is approximated at 50-year return period. This study aims to determine the flood inundated area along the Cagayan de Oro River considering the proposed dike system under a Sendong scale flood. A high resolution Digital Terrain Model (DTM) derived from Light Detection and Ranging (LiDAR) data was used to extract the topography and river geometry along the channel with the use of HEC-GeoRAS. Flood profiles were then determined using a one-dimensional steady-state flow model through HEC-RAS. The model was calibrated and validated using the actual Pablo and Sendong flood maps. The hydraulic model was then used to simulate water-surface elevations and then combined with the DTM to obtain the spatial extent and flood depths. After running through 66 models, the final model is used to simulate the flood behavior with the proposed dike system. Results show that majority of the areas along the river are protected by the dike, thus conforming to the Pablo scale flood design. However, under a Sendong flood, results show that some areas along barangays Carmen, Balulang and Macasandig could be flooded, with a total area of approximately 37 hectares. It is recommended that concerned government agencies revisit and review the design details before full implementation to ensure a sustainable flood mitigation project.