The River Authority Floodplain Viewer

This Floodplain Viewer was created to display floodplain data downloaded from the Federal Emergency Management Agency (FEMA). Below are the layer available to view in this mapping application. Layers: Base Flood Elevation (BFE): Base Flood Elevations for the 1% annual chance flood Stream Centerlines (NFHL):Location and attributes for hydrography features shown on FIRM as lines. The S_Wtr_Ln table contains information about surface water linear features. The spatial elements representing surface water line features are lines. Normally stream centerlines will be represented as line features. However, the main purpose of the S_Wtr_Ar table and the S_Wtr_Ln table is to provide a cartographic depiction of the surface water features for visual interpretation of the mapping data. As a result, the method for structuring surface water features as lines or polygons is very flexible. Lake shorelines and stream channel banks used to show lakes and wide rivers may be represented as polygons. However, they may be represented as lines based on the structure of the data received and the mapping partner’s discretion. Surface water features may appear in either the S_Wtr_Ar table or the S_Wtr_Ln table or both. The hydrologic structure of the modeled stream network will be represented by the S_Profil_Basln layer. This information is used in the Transect Locator Map and the FIRM Panel Index in the FIS report, as well as the FIRM panels. FIRM Panel: The spatial entities representing FIRM panels are polygons. The polygon for the FIRM panel corresponds to the panel neatlines. Panel boundaries are generally derived from USGS DOQQ boundaries. As a result, the panels are generally rectangular. In situations where a portion of a panel lies outside the jurisdiction being mapped, the user must refer to the S_Pol_Ar table to determine the portion of the panel area where the FIRM Database shows the effective flood hazard data for the mapped jurisdiction. This information is needed for the FIRM Panel Index and the following tables in the FIS report: Listing of NFIP Jurisdictions, Levees, Incorporated Letters of Map Change, and Coastal Barrier Resources System Information. The spatial entities representing FIRM panels are polygons. The polygon for the FIRM panel corresponds to the panel neatlines. Panel boundaries are generally derived from USGS DOQQ boundaries. As a result, the panels are generally rectangular. FIRM panels must not overlap or have gaps within a study. In situations where a portion of a panel lies outside the jurisdiction being mapped, the user must refer to the S_Pol_Ar table to determine the portion of the panel area where the FIRM Database shows the effective flood hazard data for the mapped jurisdiction. This information is needed for the FIRM Panel Index and the following tables in the FIS report: Listing of NFIP Jurisdictions, Levees, Incorporated Letters of Map Change, and Coastal Barrier Resources System Information. Flood Hazard Zones (FEMA - NFHL): Flood hazard areas identified on the Flood Insurance Rate Map are identified as a Special Flood Hazard Area (SFHA). SFHA are defined as the area that will be inundated by the flood event having a 1-percent chance of being equaled or exceeded in any given year. The 1-percent annual chance flood is also referred to as the base flood or 100-year flood. To download Flood Zones, please go to the FEMA website here. Please do not delete or modify this application.