Evaluation of high-resolution digital elevation models for creating inundation maps

by Wonkovich, Mark A.

Dr. Enrique Gomezdelcampo, Advisor The Village of Pemberville, Ohio experiences frequent flooding. Accurate flood maps are needed to reduce damage caused by these floods. Photogrammetry software was used to create a high-resolution DEM using two overlapping USGS NAPP aerial photographs each with resolutions of 1:40,000 and scanned at 1800 DPI. The resulting DEM had a resolution of 0.57 m (1.87 ft) and a minimum detectible elevation of 0.95 m (3.1 ft). HEC-GeoRAS was used to produce cross-sections of the North Branch of the Portage River and an inundation map of a 100year flood from the high-resolution DEM. The inundation map was compared to a 100-year flood inundation map produced with ground surveyed cross-sections provided by TMACOG and the FIRM for Pemberville. The datasets produced flood profile elevations of 196 m (643 ft) along the North Branch of the Portage River in the Village of Pemberville, which is the same as on the FIRM. When compared areally, the high-resolution DEM data produced larger flood extents than both the surveyed data and the FIRM of the village due to the length and distance of the cross-sections. Different lengths and large distances between cross-sections can cause large changes in the width of the bounding polygon, not accurately representing the floodplain, and limiting the extent of the estimated inundation. iii