Patalan River Basin Flood Plains Exposure and Vulnerability Assessment of Buildings Extracted from Lidar Derived Datasets

Abstract

Abstract: Philippines, as it is known to be a stopover for Pacific typhoons, is frequently threaten by flood and landslide that endangers the lives of many Filipinos. Great amount of monetary resources are being used up annually because of incidents by annual heavy downpour in this country. The population, their source of revenue and the area are the ones affected by these unfortunate events that causes the country for millions of peso every year. In this regard, there is an obvious need for methods and strategies that will alleviate adverse situations and which will protect human lives, properties and social infrastructure against disaster phenomena. Different important parameters in disaster risk management such as earth observations, Light Detection and Ranging (LiDAR) and Geographic Information System (GIS) were integrated and utilized in this study. This study dealt with mapping and assessment of buildings that might possibly be exposed and vulnerable to flooding based on the simulated flood maps at different rainfall scenarios in Patalan River Basin, Pangasinan, Philippines. The assessment was done through GIS overlay analysis of the CLSU PHIL-LiDAR 1 Project outputs, the 3D building GIS database and flood hazard maps. The 3D building GIS database was generated through processes and analysis of various datasets that include 1m resolution LiDAR Digital Elevation Models (DEMs), geo-tagged video captured data and high resolution images in Google Earth. The flood hazard maps with different hazard levels were generated with the use of flood models developed using the combined HEC HMS and HEC RAS. Results of this study were series of flood exposure maps and vulnerability maps with statistics at different rainfall scenarios. The number of houses, businesses and other types of building at risk of being flooded was quantified. It was observed that buildings exposed and vulnerable to flood are highest at 100 year return period. With the total of 129,800 building features extracted, results show that at 100 year return period there will be 61,377 buildings, 16,806 buildings and 23 buildings at low, medium and high hazards, respectively. Moreover, also at 100-year return period, a total of 12,569 buildings, 8,628 buildings and 17,795 buildings were identified that had high vulnerabilities to flood in terms of height at low, medium and high hazards, respectively. These produced maps can provide valuable information to the local government units and the communities around Patalan river basin in their flood disaster management through appropriate and riskconscious development in order to prevent further build-up risks. Through these maps, it is easier to disseminate information that is more realistic to the residents about the hazardous areas and to help them act on warning and evacuating measures. Keywords: Geographic Information System, flood, database, exposure, hazard