UNDERSTANDING THE IMPACTS OF STORM INDUCED FLOODING AT THE LOCAL LEVEL THROUGH FLOOD MODELLING WITH SAR DEM, LIDAR DTM & DSM, HEC HMS AND HEC RAS

Flooding has long been considered to be one of the deadliest natural disasters. In large river basins, flooding can submerge a whole city and cause irreparable damage to human lives and properties. The same can be said at the local level where a small creek can submerge a whole barangay, especially if the creek receives large volume of water from the upstream that are beyond its capacity. In this paper, we analyzed the physical impacts of flooding caused by the overflowing of Lemon Creek to the surrounding local community in Butuan City, Philippines. The physical impacts were analyzed in terms of flood depth and inundation extent during heavy rainfall caused by tropical storms/typhoons. In this study, we focused on the flooding impacts of Tropical Storm Agaton (January2014) and Seniang (December 2014). First, we developed a HEC HMS based hydrological model of the Lemon Creek watershed to determine the volume of water flowing into the creek during the storm durations. The HEC HMS model was developed using a 10m SAR DEM for watershed and stream delineation and a Landsat 8 OLI image for land cover parameter derivation. Discharge measurements were used to calibrate and validate the model. Then, we developed a HEC RAS model to simulate the overflowing of the creek during the storm events, with the HEC HMS simulated discharge hydrographs as inputs. A 1m resolution LiDAR Digital Terrain Model (DTM) acquired before the storms was used in generating the geometrical parameters of the HEC RAS model, and as input in the flood depth and inundation mapping. Results of the integrated HEC HMS HEC RAS flood modeling showed the extent of flooding during Agaton and Seniang. Using location of structures digitized from a LiDAR Digital Surface Model (DSM), the severity of the impacts of flooding to the local community was determined by counting the number of structures inundated during the onslaught of the tropical storms.