Flood Inundation Mapping for St. Mary's River in Fort Wayne

In partnership with the City of Fort Wayne, the U.S. Geological Survey and NOAA's National Weather Service, we are glad to announce on-line access to a new Flood-Forecast Inundation Map for the St. Marys River in Fort Wayne.

The interactive web-based tool, called a “flood inundation map library” was created from a computer model of the St. Mary’s River developed by U.S. Geological Survey scientists – the maps were technically reviewed by the National Weather Service, The City of Fort Wayne, and the Maumee River Basin Commission. The map library will help identify where the potential threat of floodwaters is greatest, providing key information to the Federal Emergency Management Agency and state and local officials to help them make quick decisions about when and how to evacuate residents threatened by rising floodwaters.  State and local emergency managers will be able to use the interactive tool to better focus flood response and resource recovery and to swiftly assess evacuation routes.

Because this new tool is so critical during floods, it is available online from two sources – this provides built in back-up in the event of a problem with either service.

U.S. Geologic Survey:

For more information and explanation of the use of the inundation map can be found by watching this

User guide video on


Streamgage and Flood-Forecast Inundation Map Libraries

Frequently Asked Questions

What is the intended purpose of these flood inundation map libraries? The maps are designed for pre-flood planning activities and real-time flood event response. The National Weather Service (NWS) and U.S. Geological Survey (USGS) provide these maps “as-is” for a quick reference, emergency planning and response tool. The maps allow users to look at water level or “stage” data from a USGS streamgage or a National Weather Service flood forecast point and visualize the estimated extent of flooding on the landscape in the area studied for a given stage. These maps are not intended for and should not be used for navigation, regulatory, permitting, or other legal purposes.

How accurate are these maps? Map accuracy is expressed in terms of the depth range. This accuracy is entirely dependent on the quality of the underlying data. The depth range can be queried by clicking on the map to expose the depth range- for example, “2.0 to 4.0 feet.”

What data and tools are used to produce the maps?   NWS and USGS work to use the best available data and tools to create these maps. The underlying data are based on high-resolution ground terrain information, detailed river channel and bridge information, and computer models that simulate water levels all along the stream based on a given streamflow (volume of water passing a point on the stream per unit of time).

Since these maps are pre-computed, are there real-world uncertainties which are not captured into the maps?   The flood maps, which are pre-computed for a wide-range of flows for a river gage, show the extent of flooding when the water elevation reaches the pre-computed river stage. Since NWS provides flood forecast which are based on current and forecast hydrometeorological conditions for rainfall and runoff, most uncertainty are factored into the river forecast. However, flooding can occur from other weather and hydrologic phenomena, which might not be captured into the hydrologic forecast, such as dam break, debris floods, or ice-jams. Since these types of floods cause significant changes in the river channel and results in varying flood flows, the extent of actual flooding could differ from what was estimated on these pre-computed maps.

Do these maps have anything to do with flood insurance? No – these maps were designed as a quick reference for emergency planning and response tool with respect to the USGS Streamgage and NWS River Forecast. These maps are not used to enforce floodplain regulations or to determine the flood insurance rate zone, which the Federal Emergency Management Agency (FEMA) delineates for the National Flood Insurance Program (NFIP). For more information on the NFIP, visit www.floodsmart.gov.

My house or business is shown in the shaded area depicting flooding for certain stages – does that mean the structure is completely submerged? Not necessarily – it just means that the structural footprint of the house or business is inundated with floodwaters of varying depths. The NWS and USGS flood inundation map viewers show the estimated depth of floodwaters at a given point on the landscape and estimates this range relative to an observed and/or forecast river gage– for example, If you click on the map where your house is located and if the range of depth is given as “2.0 to 4.0 feet,”, this would indicate that model had estimated flood­waters to be about 2 to 4 feet deep on the ground where your house sits for that particular river gage stage.

Why are their two separate flood inundation map Internet viewers – one hosted by the NWS and one hosted by the USGS?   The NWS have been collecting user requirements for the development of the NWS AHPS Flood Inundation Mapping Viewer for over 10 years, as a result of the Inland Flood Forecast and Warning Act of 2002. In the fall of 2007, NWS released the NWS AHPS Flood Inundation Mapping Services and continues to collect user requirements through AHPS Feedback, Customer Satisfaction Surveys, and various outreach mechanisms. In late 2010, USGS joined NWS by expanding the flood inundation mapping services and producing flood inundation maps for Scientific Investigation Reports.   Both theNWS and USGS have been piloting the development of new science and technology to develop flood inundation maps that are connected to river forecasts and streamgages.   An advantage of having maps available through separate viewers is that redundancy is provided – if one server fails, the other viewer is hosted on completely separate servers. Users may  note the viewers’ different look, but the maps for a given stage are exactly the same in extent and depth.

Will there be a common viewer for Flood Inundation Mapping Service? Under the auspices of the Integrated Water Resources Science and Services (IWRSS), the National Weather Service (NWS) is committed to working with the USGS, USACE, and FEMA to develop a Federal Flood Inundation Mapping Service. Toward this end, a draft scope of work has been developed and an IWRSS team will be assembled to define the requirements of this service which shall include recommendations for the operational display and dissemination of flood inundation/risk maps. Until the IWRSS FIM team completes their recommendations and the IWRSS consortium delivers a common solution, NWS supports implementation of the Forecast Flood Inundation Map (FIM) libraries onto the Advanced Hydrologic Prediction Service (AHPS) web portal. It is expected that, in time, FIM libraries developed for and available via the AHPS portal will be transitioned to IWRSS Federal Flood Inundation Mapping Service. Given this, http://water.weather.gov/ahps/ remains the operational website for the NWS partnered FIM libraries. The USGS Mapper for FIM libraries is available at: http://wim.usgs.gov/FIMI/FloodInundationMapper.html.

Why do some streams in my area have these flood inundation map libraries but others do not?  The flood inundation map libraries are developed for stream locations where the data and cooperator funding are available. The required data include high-resolution digital elevation models showing terrain data,  structural data for bridges, dams, floodwalls, and/ or levees,  a USGS streamgage , an associated NWS flood forecast or warning location, and various hydrologic data such as stage/flow rating curves, high-water mark surveys, and long term streamgage data records to calibrate the computer models.   Flood inundation mapping projects are complex and similar to flood studies, which require staff time and resources to conduct the investigation and produce the results. Since there are no appropriations to produce these flood inundation map libraries, the projects require funding from outside cooperators. The NWS and the USGS are striving to find partners to share resources for the development of flood inundation mapping libraries for streamgages and flood forecast/warning locations.



Page created by: Michael Lewis
Last Update: October 24, 2012

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