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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.

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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.

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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.

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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.

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

• Flood-inundation mapping for the Blue River and selected tributaries in Kansas City, Missouri, and vicinity
• Flood-inundation maps for Indian Creek and Tomahawk Creek, Johnson County, Kansas
• Flood-inundation maps for the Schoharie Creek at Prattsville, New York

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

• USGS Flood Information
• USGS Flood Inundation Mapping
• USGS 3D Elevation Program (3DEP lidar mapping)