UNH Floodplain

New Hampshire has more than 16,000 miles of rivers and streams and the state's settlement pattern is confluent with these locations. Communities developed along the waterways that provided mills with power and transportation. As a result of this development pattern, the floodplains of the state were rapidly settled. The shift to industrialization during the mid-nineteenth century compounded the problem, residents moved to the floodplains of the cities and larger villages. Such encroachment leads to flooding problems, as the floodplains naturally extend the watercourses during significant storm events.

Since October of 2005, New Hampshire has experienced three presidential disaster declarations. These and prior events are captured in the table below.

New Hampshire’s Flood History
Date	Area Affected (River Basins or Region)	Recurrence Interval (yr)	Remarks
December, 1740	Merrimack	Unknown	First recorded flood in New Hampshire
October 23, 1785	Cocheco, Baker, Pemigewasset, Contoocook and Merrimack	Unknown	Greatest discharge at Merrimack and at Lowell, MA until 1902
March 24-30, 1826	Pemigewasset, Merrimack, Contoocook, Blackwater and Ashuelot	Unknown
April 21-24, 1852	Pemigewasset, Winnespaukee, Contoocook, Blackwater, and Ashuelot	Unknown	Merrimack River at Concord - highest stream stage for 70 years. Merrimack River at Nashua - 2 feet lower than 1785
April 19-22, 1862	Contoocook, Merrimack, Piscataquog, and Connecticut	Unknown	Highest stream stages to date on the Connecticut River; due solely to snowmelt
October 3-5, 1869	Androscoggin, Pemigewasset, Baker, Contoocook, Merrimack, Piscataquog, Souhegan, Ammonoosuc, Mascoma, and Connecticut	Unknown	Tropical storm lasting 36 hours. Rainfall, 6-12 inches
November 3-4, 1927	Pemigewasset, Baker, Merrimack, Ammonoosuc and Connecticut	25 to >5O	Upper Pemigewasset River and Baker River - exceeded the 1936 flood. Down stream at Plymouth - less severe than the 1936 flood
March 11-21, 1936	Statewide	25 to > 50	Double flood; first due to rains and snowmelt; second, due to large rainfall
September 21, 1938	Statewide	Unknown	Hurricane. Stream stages similar to those of March 1936 and exceeded 1936 stages in Upper Contoocook River
June, 1942	Merrimack River Basin	Unknown	Fourth flood recorded in the lower Merrimack River basin at Manchester, NH
June 15-16, 1943	Upper Connecticut, Diamond and Androscoggin	25 to >50	Intense rainfall exceeding 4 inches; highest stream stages of record in parts of the affected area
June, 1944	Merrimack River	Unknown	One of the five highest known floods at Manchester on the Merrimack
November, 1950	Contoocook River and Nubanusit Brook	Unknown	Localized storm resulted in flooding of this area
March 27, 1953	Lower Androscoggin, Saco, Ossipee, Upper Ammonoosuc, Israel, and Ammonoosuc	25 to>50	Peak of record for the Saco and Ossipee Rivers.
August, 1955	Connecticut River Basin	Unknown	Heavy rains caused extensive damage throughout the basin area
October 25, 1959	White Mountain Area; Saco, Upper Pemigewasset and Ammonoosuc Rivers	25 to >50	Largest of record on Ammonoosuc at Bethlehem Junctions; third largest of record on the Pemigewasset and Saco Rivers
December, 1959	Piscataqua - Portsmouth	Unknown	Northeaster brought tides exceeding maximum tidal flood levels in Portsmouth. Damage was heavy along the coast
April, 1960	Merrimack and Piscataquog	Unknown	Flooding resulted from rapid melting of deep snow cover and the moderate to heavy rainfall. Third highest flood of record on the rivers
April, 1969	Merrimack River Basin	Unknown	Record depth of snow cover in the Merrimack River Basin and elsewhere resulted in excessive snowmelt and runoff when combined with sporadic rainfall
February, 1972	Coastal Area	Unknown	Coastal area was declared a National Disaster Area as a result of the devastating effects of a severe coastal storm, damage was extensive
June, 1972	Pemigewasset River	Unknown	Five days of heavy rain caused some of the worst flooding since 1927 along streams in the upper part of the State, damage was extensive along the Pemigewasset River and smaller streams in northern areas
June 30, 1973	Ammonoosuc River	25 to > 50	Northwestern White Mountains
April, 1976	Connecticut River	Unknown	Rain and snowmelt brought the river to 1972 levels, flooding roads and croplands.
March 14,1977	South-central and Coastal New Hampshire	25 to 50	Peak of record for Soucook River
February, 1978 (“The Blizzard of ‘78)	Coastal New Hampshire	Unknown	Nor’easter brought strong winds and precipitation to the entire state. Hardest hit area was the coastline, with wave action and floodwaters destroying homes. Roads all along the coast were breached by waves flooding over to meet the rising tidal waters in the marshes
July, 1986 - August 10,1986	Statewide	Unknown	FEMA DR-71l-NH: Severe summer storms with heavy rains, tornadoes; flash flood and severe winds
March 31 - April 2, 1987	Androscoggin, Saco, Ossipee, Piscataquog, Pemigewasset, Merrimack & Contoocook River	25 to >50	Caused by snowmelt and Sense rain Precursor to a significant, following event
April 6-7, 1987	Lamprey River and Beaver Brook	25 to >50	FEMA DR-789-NH: Large rainfall event following the March 31- April 2 storm.
August 7-11, 1990	Statewide	Unknown	FEMA DR-876-NH: Series of storm events from August 7-11, 1990 with moderate to heavy rains during this period produced widespread flooding.
August 19, 1991	Statewide	Unknown	FEMA DR-917-NH: Hurricane Bob struck New Hampshire causing extensive damage in Rockingham and Strafford counties, but the effects were felt statewide.
October, 1996	Northern and Western Regions	Unknown	FEMA DR-1077-NH: Counties declared: Carroll, Cheshire, Coos, Grafton, Merrimack, and Sullivan.
October – November, 1995	Northern and Western Regions	Unknown	FEMA DR-1144-NH: Counties declared: Grafton, Hillsborough, Merrimack, Rockingham, Strafford, and Sullivan.
June — July, 1998	Central and Southern Regions	Unknown	FEMA DR-1231-NH: Series of rainfall events. Counties declared: Belknap, Grafton, Carroll, Merrimack, Rockingham and Sullivan. (1fatality) (Several weeks earlier, significant flooding, due to rain and rapid snowpack melting, occurred in Coos County, undeclared in this event. Heavy damage to secondary roads occurred)
September 18- 19, 1999	Central and Southwest Regions	Unknown	FEMA DR-1305-NH: Heavy rains associated with Tropical Storm/Hurricane Floyd. Counties declared: Belknap, Cheshire and Grafton.
July 21 - August 18, 2003	Southwestern Region	Unknown	FEMA-1489-DR: Severe storms and flooding occurred in Cheshire and Sullivan counties. Public Assistance provided for repair of disaster damaged facilities.
October 7 -16, 2005	Southwestern Region	Exceeded 100 in some areas	FEMA-1610-DR: Heavy rains associated with Tropical Storm Tammy and Subtropical Depression 22 resulted in 6-15 inches of rain.
May 13-15, 2006	Central and Southern NH	Exceeded 100	FEMA-1643-DR: Heavy rainfall 8-16 inches
April 27, 2007	Statewide	100	FEMA-1695-DR: Severe storms and flooding, starting on April 15th.
August 11, 2008	Central and Southeastern Regions	Unknown	FEMA-1782-DR: Severe storms, tornado, and flooding, starting on July 24th.
September 5, 2008	Northern Region	Unknown	FEMA-1787-DR: Severe storms and flooding, between July 24th and August 14th.
October 3, 2008	Central and Southern Regions	Unknown	FEMA-1799-DR: Severe storms and flooding, starting on September 6th and 7th and continuing.
May 12, 2010	Rockingham County	10 to 25	FEMA-1913-DR: Severe storms and flooding, between March 14th and 31st.

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