Using topographic lidar to map flood risk from storm-surge events for Charlottetown, Prince Edward Island, Canada

Abstract

As part of a recent project to determine coastal impacts of climate change and sea-level rise on Prince Edward Island (PEI), airborne scanning laser altimetry (lidar) was employed to acquire high-resolution digital elevation models (DEMs) and other landscape information. The study area included both the Charlottetown urban area and an extensive portion of the rural North Shore of PEI. Problems with the lidar data included data gaps and incorrect classification of "ground" and "non-ground" laser hits along the waterfront. Accurate representation of wharves and other waterfront features in the DEM was achieved by combining "ground" and "non-ground" data. The importance of calibration and validation in lidar data acquisition and interpretation was demonstrated by three independent validation exercises that uncovered and adjusted for a vertical offset attributed to calibration problems. The ground DEM was adjusted to hydrographic chart datum and used to model flood extent at three storm-surge water levels, one observed in the record storm of 21 January 2000 and two higher levels representing flood scenarios under rising sea level. Flood modelling was executed in a geographic information system (GIS) on the gridded ground DEM. The resulting binary grids were vectorized along the flooding limit. Low-lying areas isolated from free exchange with the harbour were excluded from the flood area. Vectors depicting the storm-surge water lines for the three flood scenarios were implemented on the geographic information system (GIS) in the city planning department and overlain on property boundary and assessment layers. This study demonstrated that validated DEMs derived from airborne lidar data are efficient and adequate tools for mapping flood risk hazard zones in coastal communities.