USGS Innovation in Inundation Mapping

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Flood Information to Power Community Decisions


In recognition of World Water Day and in conjunction with the White House Water Summit, the U.S. Geological Survey is raising awareness of water issues and potential solutions in the United States.


The U.S. Geological Survey helps communities protect lives and property by providing cutting-edge tools and information that enable communities to understand local flood risks and improve mitigation decisions.

“Floods are the leading cause of natural-disaster losses in the United States,” said Jerad Bales, USGS Chief Scientist for Water. “Annual flood losses average almost $8 billion and more than 90 fatalities per year. More than 75 percent of declared Federal disasters are related to floods.”

Although flood-related fatalities have declined during recent years due to improved forecasting and early warning systems, economic losses have continued to rise with increased development in flood-hazard areas. With an electronic connection to USGS real-time stream data, USGS flood inundation maps allow communities to know — on a street-by-street, block-by-block basis — the extent of any potential flood and, in times of emergency, identify at-risk areas and resources in advance of arriving floodwaters.

Image: Maple River Flooding

Embden farm landowners durring Maple River flooding.
Public domain

Building the basis for shared flood knowledge

Ahead of the event, flood inundation maps of potential flooding scenarios must be carefully constructed often using high-accuracy lidar data provided by the cooperative USGS 3D Elevation Program. Underpinned with these highly detailed maps of the topography, the series of maps that apply to a specific stream (or river) segment and a range of stream levels are seamlessly arranged in electronic flood inundation map libraries. These libraries can easily be accessed through the internet by anyone, including, importantly, local elected leaders, urban planners and engineers, police and fire personnel, and other emergency managers.

Having a flood inundation library in place for a community not only allows all of its citizens to understand the shared flood risk and make cost-effective mitigation decisions, but it can substantially reduce the cost of flood insurance for those communities that participate in FEMA’s community rating system. The information also allows first-responders to target areas of highest risk during a flood.

Image: Flooding in Downtown Minot, N.D.

As the Souris River flooded during the early summer of 2011, it overcame levees in the city of Minot, N.D., causing about 11,000 people to evacuate their homes. The record-breaking flood crested on July 25 at over 26,000 cubic feet per second (cfs) and 24 feet - nearly 13 feet over flood stage - according to U.S. Geological Survey streamgages in the area.
"An above normal winter snowpack in addition to much above normal precipitation in May and June led to the record flooding along the Souris River," said Steve Robinson of the USGS North Dakota Water Science Center.
The USGS collects data from more than 100 streamgages in North Dakota, most of which provide real-time data that is transmitted every hour. For the latest and most accurate streamflow data for the Souris River Basin in the U.S. and Canada, visit the real-time streamflow web page.
Public domain

Expanding nationwide collection of lidar data as a critical component of the US Topo map series makes constructing flood inundation map libraries more feasible and efficient than ever before. More than 100 such libraries for flood-prone communities in 20 states will be available by the end of this year.

screenshot of the flood inundation mapper web tool

The recent (3/18/16) real-time report from the USGS Flood Inundation Mapper for Petersburg, IN, showed that the moderate flood would continue to decline in the hours ahead.

For example, these flood inundation map libraries have been released in the past month.

Start with streamgages

A recently published post-event report (2016) on flooding in South Carolina in October 2015 illustrates the thorough analysis that underpins USGS flood science and flood inundation mapping. During and after the four-day storm event, USGS streamgages recorded all-time peaks of streamflow record at 17 locations. New flood inundation maps can help South Carolinians take steps to prevent or reduce future flood damage in the areas. Other reports of recent floods as well as a current view of flood conditions across the Nation can be found at the USGS Water website.

The USGS operates and maintains a network of more than 8,100 streamgages across the Nation that provides essential streamflow information over the internet on a near real-time basis.

USGS hydrologists and technicians regularly measure flood flows and update the relationship between river stage heights and streamflow readings to track constantly changing conditions and ensure that accurate data are available at all times.

Learn more