GIS-ing Flood Data -ing Making valuable information in paper studies accessible By Mehdi Mashud Khan, Randall Vogel, and Ronald O. Edwards, polk County Board of County Commissioners Polk County, Florida, has acquired a significant number of detailed local flood studies over the last 20 years. These studies—the result of a county requirement—are being converted from paper documents to GIS layers to provide valuable flood protection information to county residents. Flooding is one of the most common natural hazards in Polk County, as it is in many other parts of the United States. Approximately 46 percent of the county is located in one of the Federal Emergency Management Agency (FEMA) Special Flood Hazard Area (SFHA) designations. A significant percentage of the county's population lives or works in areas that are at risk of flooding. Because Polk is in Florida, it is also susceptible to seasonal hurricanes that can cause severe flooding. In 2004, three hurricanes that passed through the county resulted in standing water all over the county and caused rivers to overflow and flood adjacent communities. Any prolonged rainfall has the potential to result in flooding. The county's flat topography, combined with expanding development, causes storm water to reach buildings quickly because water moves across the surface more rapidly than it can be absorbed into the ground. The same factors also delay the departure of floodwaters. Mitigation Activities To minimize flood damage, Polk County has undertaken flood protection activities (e.g., periodic ditch and channel cleaning, maintaining flood-prone areas as open space) along with the introduction of flood protection regulations. As part of this effort, the county requires that new residential buildings or buildings that are substantially improved be elevated one foot above the base flood elevation (BFE). This ordinance means that information on the flood zone and the base flood elevation for a site must be known for these properties. To help determine the flood zones and BFEs, FEMA provides paper and online maps. In some cases, these maps may supply sufficient information. However, in many instances, FEMA maps lack sufficient detail because they were prepared 10 or more years ago using 5- to 10-foot contour data. At that scale, a parcel or a small piece of land can easily be lost. Although FEMA maps were updated in 2000, many updated maps are based on maps prepared in 1983. FEMA maps might recognize a potential flood hazard area but lack detailed information such as BFEs or the extent of flooding. In a worst-case scenario, FEMA maps may have completely inaccurate information or lack any information at all. County Response The county has addressed this issue by requiring detailed flood studies for any proposed development larger than five acres or 50 lots. Over the years, the county has acquired a significant number of studies for many developments within its jurisdiction. These studies, submitted and stored in the county in paper format, are a great resource for the county, not only for the developments for which they were created but 34 ArcUser Fall 2010 www.esri.com