Abstract
Coastal cities in the Philippines are highly exposed to flooding due to rapid urbanization, sea-level rise, and intense typhoons. Conventional defenses such as dikes and levees provide immediate protection but raise peak water levels, transfer risks downstream, and require costly long-term maintenance. Nature-based solutions (NBS), including mangrove rehabilitation and riparian reforestation, are emerging for their ability to attenuate flood peaks while delivering ecological benefits. Yet, limited process-based modeling directly compares the hydraulic performance of conventional, nature-based, and hybrid approaches under uniform design conditions. This study evaluates flood mitigation strategies for the Antiao River Catchment in Catbalogan City, Samar, under a 100-year design flood using HEC-RAS 2D hydraulic modeling. LiDAR and IFSAR terrain data, supplemented with field bathymetry, informed the model. Design hydrographs validated by the Creager method and tidal stages defined the boundary conditions. Validation against Typhoon Haiyan (2013) inundation heights showed only 2–3% deviation. Seven scenarios were simulated: baseline, full-protection dikes (FPD), dikes with retarding basins (FPDRB), dikes with mangroves (FPDM), dikes with upstream reforestation (FPDR), and a hybrid combination (FPDMR). Results show that FPDRB achieved the lowest peak water surface elevation (3.03 m; 3.20 m dike) but required extensive land. The hybrid FPDMR approach reduced WSE to 3.13 m (3.30 m dike), nearly matching FPDRB while avoiding major land-use trade-offs. Findings demonstrate that integrated green–grey strategies can provide robust flood protection while delivering ecological co-benefits, making them practical and sustainable options for climate resilience and policy-making in Philippine coastal cities.
Presenters
Jeffrey ReyesProject Technical Assistant VI, Department of Science and Technology – Philippine Atmospheric, Geophysical and Astronomical Services Administration, Philippines
Details
Presentation Type
Paper Presentation in a Themed Session
Theme
Technical, Political, and Social Responses
KEYWORDS
FLOOD RISK MANAGEMENT, CLIMATE RESILIENCE, NATURE-BASED SOLUTIONS, HYDROLOGY, HYDRAULICS
