PEMBROKE, N.H. -- A new flood preparedness tool that will help emergency managers improve flood warnings and response is now available for a 16.5-mile reach of the Suncook River in southeastern New Hampshire that has frequently flooded adjacent homes.
The new web-based tool, developed by U.S. Geological Survey scientists, shows flood inundation maps to identify where the potential threat of floodwaters is greatest. The maps show the land areas and features that would likely be submerged and the expected depth of the floodwaters when a streamflow gauge upstream rises. The maps are part of a national USGS effort to help emergency managers quickly assess evacuation routes, determine when and how to evacuate residents threatened as floodwaters rise, and better focus flood response and recovery efforts.
"Floods are the most expensive natural disaster that we face in the U.S., affecting all 50 states and costing more than $2.7 billion dollars annually averaged over the past 10 years according to government estimates," said USGS Director Marcia McNutt. "Investing in science-based preparedness tools like the online flood inundation maps is a smart way to help everyone know the quick decisions to make to spare lives and property."
The USGS is partnering with the National Weather Service, the U.S. Army Corps of Engineers and FEMA to develop comparable flood inundation maps in locations across the country identified to be at high risk for flooding.
The USGS completed the Suncook River maps in partnership with the New Hampshire Department of Safety, Division of Homeland Security and Emergency Management. The maps extend from the USGS streamgage at Depot Road in North Chichester to the Merrimack River. They include portions of the towns of Chichester, Epsom, Allenstown, and Pembroke and the community of Suncook. The maps show the extent and depth of flooding expected in these towns, for 10 river levels, starting when the North Chichester gauge reaches seven feet, up to a crest of 18 feet. Flood stage is at seven feet.
"I see these maps as a great new tool for local and state emergency personnel, residents, and landowners to prepare for, and respond to flooding," said Christopher Pope, Director of the NH Division of Homeland Security and Emergency Management.
The North Chichester streamgage is also a National Weather Service flood forecast gauge. The NWS combines the current stage with its precipitation forecasts to predict the Suncook River’s crest at this location. Based on these predictions, anyone can use the new flood inundation maps to estimate areas along the Suncook River that would be flooded.
"A number of recent studies of the Suncook River since the flooding of 2006 and 2007 made the flood inundation mapping possible," said Robert Flynn, USGS hydrologist and author of the maps.
The area of the Suncook River shown on the maps has flooded many times, most notably in 2006, 2007, and 2010. On May 15, 2006, the flooded river changed course, forming a new river channel through a sand and gravel pit, shortening the river’s length, and increasing the potential flood hazards to communities downstream.
"This shortening of the river means that there is a greater potential for flooding to adjacent communities because of faster river flows in the vicinity of the sand pit, greater erosion of the river banks and stream channel, and piling up of sediment downstream," said Flynn.
The flood inundation map web-based tool can be found online. The Suncook River inundation report, which contains links to current USGS stream-stage data and forecasted stream-stage data from the NWS, is available online. NWS forecasted flood levels for the Suncook River are available online.
The Flood Inundation Map is one of a series of flood preparedness tools that the USGS has developed to help emergency and resource managers and the public prepare for potential flooding and track water levels as they rise. The map is based on data from the USGS's nationwide streamgage network that monitors the water level and flow of the nation's rivers and streams.
WaterAlert and StreaMail are two other online resources that provide residents with timely information about river conditions at important locations. Subscribers have a number of options to choose from on how to get the information, and can have emails or texts sent to them automatically whenever a critical threshold is reached. With these tools, emergency managers, resource managers and the public can stay informed and help keep themselves or others out of harm's way by keeping up to date of local conditions.