Developing 2D flood hazard maps in Surigao City for flood overlay

The study focused on Surigao City, which is located in an area where extreme rainfall conditions occur resulting into flooding of urbanized areas such as San Juan, Luna, Taft, Washington and Canlanipa. The study revisits the flood study in 2011 (TCAGP, 2011) and processed the previous data using two dimensional overland flow and one dimensional channel flow models in the floor plain area using FLO-2D software. Flood depth and velocity were used to define a three level flood hazard map under 2, 5, 10, 25 and 50 year rainfall return period events. High hazards were taken as having a flood depth of 1.5 meters and above or a product of depth and velocity greater than 1.5 (m2/s). This means a critical velocity of 1.0m/s is assumed for a depth of 1.5m or greater to be included in the high hazard. Based on the results, high flood depths, flood velocities and, consequently, flood hazard zones were found to be concentrated along the Surigao River and areas adjacent to it. It was also found that some areas were either not classified as hazardous or set as a lower hazard, despite meeting the required depth levels, due to slower velocities. On the other hand, other areas were given higher hazard classifications, despite having relatively low water depths, due to faster velocities. As such, using depth and velocity as parameters for defining flood hazards may be better than using depth alone