Standard methods for the Iowa statewide floodplain mapping program

Abstract

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. iv TABLE OF CONTENTS LIST OF TABLES .

Coupled Hydrologic And Hydraulic Models And Applications

“…First, the Manning's coefficient of each land cover type from the NLCD 2001 dataset (Fig 3.4) is assigned with the suggested Manning's roughness coefficients as shown in Table 3.1. These dataset are provided from the work completed by the Statewide Floodplain Mapping Project (Thomas, 2011). Next, the geo-processing tools used to generate and prepare all needed inputs by the 1D-SVE solve are described into two sub-sections :) (1) Cross Sections Generator (2) Hydraulic Model Inputs Preparation…”

Characterization of agricultural floodplain scour using one-dimensional hydraulic simulation

“…The FPM Program is creating inundation maps to FEMA standards for all streams in Iowa draining greater than one square mile for the 2, 5, 10, 25, 50, 100, 200, and 500 year return periods. The maps are created using the FEMA guidelines for an approximate analysis (Thomas, 2011). Depth raster data and water surface elevation tin data are also created for each of these return periods as part of the floodplain mapping process, and they will be part of the input data for this thesis project and will be discussed further in CHAPTER 3.…”

“…The FPM project uses a 1 meter digital elevation model (DEM) of Iowa obtained with light detection and ranging (LiDAR) technology. The LiDAR DEM dataset was made available to the IFC through a partnership with the Iowa Department of Natural Resources (IDNR) and is a necessary input for all major mapping processes in the FPM program (Thomas, 2011).…”

“…The National Hydrography Dataset (NHD) is a spatial dataset that marks surface water features such as lakes, rivers, ponds, dams, and canals. This dataset is used in the FPM process to identify and name reaches (Thomas, 2011).…”

“…The National Land Cover Database (NLCD) is a spatial dataset that classifies land cover types for the entire United States. It is used to determine spatial roughness information (Thomas, 2011).…”