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Nearly $370 million in flood damages prevented in spring 2011 by Corps flood risk management projects in New England

Published June 10, 2011

CONCORD, Mass. – Flood damages amounting to approximately $370 million were prevented during the March 2011 storms by the U.S. Army Corps of Engineers, New England District flood risk management dams and local protection projects in New England.


“The New England watersheds experienced near normal to much greater than normal snowpack during the winter months of 2011 and the flood potential was considered very high as the late winter and early spring season approached,” said Paul Marinelli, chief of the Corps’ New England District Reservoir Regulation Section, in Concord, Mass. “With warming air temperatures influencing our region, the variety of storm systems affecting our watersheds produced rainfall in lieu of snowfall.”


A March 6-7 rainstorm, with significant snowmelt contribution, caused high runoff conditions especially within southern New England watersheds, Marinelli said.  The Naugatuck, Blackstone, Thames and portions of the Connecticut and Merrimack River basins within Massachusetts, experienced the highest runoff conditions.  Rainfall totals of 3 to 5 inches, along with augmented snowmelt, lead to the significant runoff conditions.  The upper watersheds in New Hampshire and Vermont did not experience significant runoff from this storm as the snowpack was able to absorb some of the rainfall resulting in minimum snowmelt contributions. 


Total damages prevented by Corps dams and Local Flood Protection Projects was about $370 million, with 92 percent attributed to Corps dams and 8 percent to Local Flood Protection Projects.


     Naugatuck, Thames and Blackstone River Basins

Approximately 2 to near 5.0 inches of rain occurred in a 24-hour period, and combined with significant snowmelt, caused flood runoff within the Naugatuck, Thames, and Blackstone River basins on March 7, 2011.  The existing snowpack contained about 4-7 inches of water and being at “ripe” densities, allowed portions of the snowpack to melt and contribute as augmented runoff, Marinelli said.


Along the Naugatuck River, all river stations rose 2 to 3 feet over flood stage, and had Corps dams not held back significant inflows, river levels would have resulted in 5 to 6 feet over flood stage. Some flood conditions along the Housatonic River in Massachusetts and Connecticut were very significant as river levels crested as the 5th highest flood in 88 years at Stevenson, Conn., cresting at 21.7 feet, which was only 2.8 feet lower than the October 1955 flood of record. Corps dams within the Naugatuck River basin utilized between 33 and 55 percent flood storage.  Along the Quinebaug River in the Thames River Basin, all river stations rose and crested just under flood stage, whereas, the Shetucket River rose to flood stage. Had the Corps dams not held back significant inflows, river levels would have resulted in 2 to 6 feet over flood stage. 


Corps dams within the Thames River basin utilized between 20 and 35 percent flood storage. Along the Blackstone River, all river stations rose and crested about 1-foot over flood stage. The Tainter Gate Dam, as part of the Woonsocket Flood Mitigation Project in Woonsocket, RI, was in constant operation during this runoff event. The Corps West Hill Dam flood storage project within the Blackstone River basin utilized about 25 percent of its flood storage. 


Total damages prevented during these events were $290,776,000 in the Naugatuck River basin, of which 95 percent were attributed to Corps dams and 5 percent to local flood protection projects. Total damages prevented during these events were $47,740,000 in the Thames River basin, of which 100 percent were attributed to Corps dams.  Total damages prevented during these events were $20,788,000 in the Blackstone River basin, of which 14 percent were attributed to Corps dams and 86 percent to Local Flood Protection Projects.  


Connecticut and Merrimack River Basin

Approximately 2 to 4 inches of rain occurred during March 6-7, and combined with some snowmelt, caused flood runoff within the Connecticut and Merrimack River basins on March 7, 2011.  The existing snowpack contained about 5-7 inches of water; however, the density was not fully ripe and as a result, the snowpack absorbed most of the rainfall within the upper watersheds in Vermont and New Hampshire, and both the main stem Connecticut and Merrimack Rivers crested below flood stage, according to Marinelli. Only the southern tributaries experienced the greatest runoff in southern New Hampshire and Massachusetts.  


Along the Contoocook River in Peterborough, New Hampshire, the river rose to just over flood stage, predominantly as a result of ice jam occurrences, and along the Ware River at Barre, Mass., the river rose to about 3.5 feet over flood stage causing significant flooding to localized properties along the river.  Corps-managed dams used between 10 and 50 percent of flood storage associated with this event.


New England District has been using the Geostationary Operational Environmental Satellite (GOES), known as GOES East or GOES-13, which became operational in April 2010 with advanced

weather imagery, as its data collection satellite, to assist the team in managing Corps dam operations. The District data collection platforms monitor pool, tailwater, river levels, ocean levels, precipitation, and air and water temperature, recording data every 15 minutes. The data collection platforms also monitor piezometer data and record these every four to six hours, depending on the site.


By collecting information about river stages and flows and their increases and decreases from 100 data collection platforms over time, the hydrologists can effectively regulate the Corps-managed dams to minimize impacts downstream. “This system assists us in deciding when to close or throttle back water flow through our network of 35 dams to provide the maximum flood damage prevention benefits to downstream areas,” Marinelli said. Through the use of real-time hydrologic data, field collected snowpack data, and exchange of information with the National Weather Service’s Northeast River Forecast Center, significant water movement can be identified, examined and predicted.


Each winter and spring, the Army engineers compile bi-weekly summaries of snow depths and their water equivalents from 100 key locations within the Connecticut, Merrimack, Thames, Housatonic and Blackstone river basins. With the information, engineers make calculations to determine snow density and comparisons are then made to averages based on over more than three decades of such readings.

The Corps has designed a system of flood risk management projects which includes 35 flood risk management dams, 112 local protection projects, and five hurricane barriers in New England. A total of 31 of 35 reservoir projects, and three of five hurricane barriers are operated and maintained by the Corps, while the remaining projects are operated and maintained by local interests.


Cumulative flood reduction damages prevented by all projects, including local protection projects, since their construction through Sept. 30, 2010 are more than $5.2 billion. These projects cost a total of $538 million to build. New England District operates and maintains 10 of 31 reservoirs for flood risk management only. Another 17 are operated primarily for flood risk management, and seasonally for recreational activities. The remaining four reservoirs are operated as multipurpose projects, including flood risk management, water supply, recreation, non-Federal hydropower, and fishery storage.


Streamflow and other project/reservoir data are available online at the Corps’ New England District website at Select New England District River Watch Section under “hot topics” or go directly to the link at:

Tim Dugan

Release no. 2011-057