Currently the Iowa Flood Center (IFC) of the University of Iowa is working in conjunction with the Iowa Department of Natural Resources (IDNR) to create statewide floodplain maps. The IFC has set up a four year plan to construct flood inundation maps for 85 of the 99 counties within the state of Iowa, with the final goal of creating maps acceptable by FEMA. High resolution statewide LiDAR information provides a base dataset from which floodplain maps are produced. Stream centerline data is extracted from a DEM produced by the LiDAR dataset. The centerline information is used in both this project and as a replacement for the USGS NHD streamline for the state. Stream flow estimation for a range of annual exceedance discharges are produced through a USGS recommended combination of regional regression analysis weighted by gage influence. Water surface elevations are produced for each of the annual exceedance discharges through the use of a HEC-RAS one dimensional steady flow model. Flood boundaries are the final product created by HEC-GeoRAS though a comparison of a TIN produced from the water surface elevations and the ground surface DEM. Final FEMA acceptable DFIRM's are produce by the IDNR and submitted to FEMA for adoption into the NFIP.

Flooding is a major hazard in the Midwest, accounting for more economic damage than any other hazard. Recent major flooding events in Iowa have created a greater need for the monitoring of floodplain areas. The objective of this paper is to evaluate flood risk through the synthesis of geospatial data with flood maps for thirteen Hydrologic Unit Codes (HUC 8s) in southwest Iowa. Using ArcGIS, exposure of ecosystem services, population, and environmental hazards can be located within the 10, 50, 100, 500 year floodplains. Additionally, the effectiveness of hydric soils as a floodplain proxy is evaluated using SSURGO soil data. An overview of FEMA HAZUS-MH 2.0 flood loss estimation software is provided and a model of the East Nishnabotna HUC 8 is evaluated. An alternative economic loss framework based on an NED land use raster and structure data is compared for the region. This study aims to provide beneficial floodplain information for development and regulation decisions.

Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps portray the height and extent to which flooding is expected to occur, and they form the basis for setting flood insurance premiums and regulating development in the floodplain. As such, they are an important tool for individuals, businesses, communities, and government agencies to understand and deal with flood hazard and flood risk. Improving map accuracy is therefore not an academic question-better maps help everyone. Making and maintaining an accurate flood map is neither simple nor inexpensive. Even after an investment of more than $1 billion to take flood maps into the digital world, only 21 percent of the population has maps that meet or exceed national flood hazard data quality thresholds. Even when floodplains are mapped with high accuracy, land development and natural changes to the landscape or hydrologic systems create the need for continuous map maintenance and updates. Mapping the Zone examines the factors that affect flood map accuracy, assesses the benefits and costs of more accurate flood maps, and recommends ways to improve flood mapping, communication, and management of flood-related data.

The objective of this project is to assess the predictive accuracy of flood frequency estimation for the Rational Method, the NRCS curve number approach, and the Iowa Runoff Chart, for applications to small Iowa streams (drainage areas of 200 acres or less). The evaluation is based on comparisons of flood frequency estimates at sites with sufficiently long streamgage records in the Midwest, and selected urban sites throughout the United States. The sensitivity of estimates to several watershed characteristics, such as soil properties, slope, and land use classification, is also explored.