S12 Effects of DEM resolution on HAZUS flood mapping for the Monongahela River: California, PA

Sunday, 23 January 2011
Timothy M. Lahmers, California University of Pennsylvania, California, PA; and K. Fredrick, T. Mueller, C. M. Kauffman, and M. S. Scott

California University of Pennsylvania, adjacent to the Monongahela River in the borough of California, PA, is vulnerable to periodic flooding. Such flooding can cause financial losses to the University and the surrounding community, and major disruptions to thousands of students during such an event. In the past, flood events have impacted the University and other parts of the Monongahela River Valley such as in 1985 and 1996. HAZards United States (HAZUS) is a disaster management tool developed by the Federal Emergency Management Agency (FEMA) that can assess losses and risks for such situations through its flood model. HAZUS flood model integrates with a Geographic Information System, and its assessments depend on estimated water levels during a flood. Because water depth is a critical predictive element, accurate elevation data are critical for the loss-assessments that HAZUS produces. While HAZUS is an extremely useful program, lack of precision with Digital Elevation Model (DEM) input can lead to inaccurate loss estimates. One solution may be Light Detection and Ranging (LIDAR) based DEMs, which provide higher resolution elevation data. The standard DEM input for HAZUS is the United States Geological Survey's (USGS) Nation Elevation Dataset (NED), which has a lower resolution than other more recent data. Coarse resolution elevations in use with NED may poorly represent reality and therefore potential flood losses. HAZUS was used in this research to evaluate the Monongahela River's 100-year flood plain through California, PA using the standard NED DEM and compared against the results made from using the LIDAR DEM. Analysis of both spatial and non-spatial products shows that NED estimates of the California, PA floodplain do a poor job at estimating the hazards of a 100-year flood. This has implications for users of HAZUS in other communities, particularly where either high-resolution elevation data or computing power to process such data are unavailable.
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