Flash Flooding and Flooding in New Hampshire, December 18 to 21, 2023

Southeast winds increased during the overnight hours on December 17th as the surface low approached the region. By daybreak on the 18th, strong to damaging onshore southeast winds impacted the entire state. Impacts were greatest across the Seacoast region of the state and on the lee-side of the White Mountains. The winds peaked in intensity early morning through noon with a 6 hour window of strong to locally damaging winds. The widespread winds, lengthy duration, and vulnerable southeast wind direction led to snapped branches, uprooted and snapped trees. This led to scattered power outages in the Seacoast Region with a relatively quick recovery of power to residents.

The Ammonoosuc River reached moderate flood stage on December 18th. The USGS river gage in Bethlehem reported a stage of 12.15 feet, the second highest crest on record since the site was established in 1940. The flooding was the result of heavy rainfall combined with snowmelt in the mountains. The combined runoff was estimated between 6 and 7 inches which moved rapidly down steep terrain over frozen ground. The river rose from 2 feet to over 12 feet within 15 hours, cresting in the early afternoon of the 18th. In upstream Bethlehem, there was flooding along several small streams and brooks. Access was cut off on River Road with flooding in multiple locations. Significant flooding occurred upstream at Twin Mountain and Zealand Campgrounds. Flooding occurred at the Stark Village Inn with basement inundation and water up to the bottom of the covered bridge in Stark.

The Ammonoosuc River reached moderate flood stage on December 18th. The USGS river gage in Bethlehem reported a stage of 12.15 feet, the second highest crest on record since the site was established in 1940. The flooding was the result of heavy rainfall combined with snowmelt in the mountains. The combined runoff was estimated between 6 and 7 inches which moved rapidly down steep terrain over frozen ground. The river rose from 2 feet to over 12 feet within 15 hours, cresting in the early afternoon of the 18th. Hardest hit areas were in Littleton off of Meadow Street where numerous businesses were impacted south of the Route 93 exit. Flooding was also reported along Union and Cottage Street at Lane House, and Littleton Water and Light. Community fields in Lisbon under several feet of water.

Severe flooding occurred in Bartlett and upstream in Hart's Location, New Hampshire on December 18th. The flooding was the result of heavy rain and rapid snowmelt along the steep slopes of the south facing mountains around Bartlett. The combined runoff from rainfall and snowmelt is estimated to be around 10 inches. The steep terrain and frozen ground resulted in very rapid runoff with flash flooding occurring along every small stream and brook in the region. The USGS river gage at Bartlett went from 3 feet at 9 PM on the 17th, to 13.8 feet by noon on the 18th. The discharge was measured over 25 kcfs, which has an annual chance exceedance of 1% to 0.2%, otherwise referred to as a 100 to 500 year flood. The river stage reached was the 3rd highest on record, and a foot below that reached during Irene in 2011. The hardest hit areas were the confluence of the Saco River, the Rocky Branch and at the confluence of the Ellis River. Route 302, a main thruway to the region closed from Glen to Jericho due to severe flooding. West Side Road was flooded along with numerous homes and camps. In Bartlett, the flood waters flooding River Street up to Route 302. Additionally, several local road closures and washouts were reported along the Saco and other small streams and brooks. There was significant damage to a campground in Bartlett and another in Glen Ellis.

Major flooding of the Moose River with an estimated rain and snowmelt between 8 and 9 inches of liquid runoff. The resultant flow was estimated around 6500 CFS, which is greater than the 0.2% annual exceedance level, or 500 year flood. The river overflowed its banks surrounding homes and flooding basements off Bellevue Place near the Gorham Airport. Additional flooding occurred on Water Street and Broadway Avenue. Flood waters topped the Route 2 bridge shutting down a major throughway in the region.

Major flooding of the Moose Brook with an estimated rain and snowmelt between 8 and 9 inches in runoff. The resultant flow is estimated over a 0.2% recurrence interval with flows between 3 and 4 kcfs. The most severe damages were near Pike Industries in Gorham, which suffered a washed-out bridge and floodwaters compromised a building. The nearby storage facility was inundated with unknown damages. Jimtown Road flooded but no reported homes where damaged. The flows overwhelmed the Moose Brook bridge overtopping onto Route 2. A large truck was picked up by the flood waters and wedged under the bridge, along with significant amounts of rocks and debris.

Heavy rain and rapid snowmelt produced around 9 inches of combined runoff. All small streams in the Presidential Range region exceeded their banks. This was true in Jefferson, New Hampshire where numerous small streams flooded Route 115 and Route 2, causing these roads to be closed.

Significant damage occurred on the Peabody River on December 18th following a heavy rain and rapid snowmelt event. The USGS river gage in Gorham went from under 100 cfs around midnight, to over 13,000 cfs by noon. The streamflows were estimated to be around the 1% annual exceedance or 100-year flood level. Rainfall amounts where estimated around 5 inches with an additional 3 inches of rapid snowmelt runoff. The ground conditions were frozen, supporting complete runoff. One home off Route 16 was deemed unlivable and a complete loss after floodwaters eroded the foundation. Property was also damaged at Great Glen Trails Outdoor Center near the headwaters. Downstream in Gorham the damage was most prevalent along Bell Street and after the confluence with the Androscoggin River. Major damage occurred downstream to the town of Shelburne.

Heavy rain and snowmelt caused rapid runoff and flooding of the Ossipee River in Effingham causing NH 153 or Province Lake Road to be closed.

Heavy rain and snowmelt caused rapid runoff and flooding from the Cold River. River overflowed the Stone House Road bridge in Chatham along the Maine and New Hampshire stateline.

Heavy rain of 2 to 4 inches fell across Rockingham County. The frozen ground caused several low lying roads to flood. Those included Colby Road from Deerlick Road to NH-111A in Danville, NH 121A in Chester, NH 43 from Cotton Road to NH-107 in Deerfield, NH-27 from Harriman Hill Road to Epping Street in Raymond, and Mammoth Road at NH-28 in Londonderry.

Heavy rain and snowmelt caused rapid runoff that flooded a section of NH 109 just west of Wakefield.

Heavy rain and rapid snowmelt combined with steep terrain to produce rapid runoff into the Ellis River. The small stream became a raging river after 6 inches of rain and 3 inches of snowmelt overwhelmed the stream system. Downstream in Jackson, properties along the river were inundated, along with several roads being damaged. The main thruway, NH Route 16, closed at mile marker 92.6, and adjacent NH 16B also flooded. Washouts were also reported in many local roads like Green Hill Road.

The Suncook River reached moderate flood stage on December 18th following heavy rain and snowmelt. The basin average rainfall was around 4 inches, causing the Suncook River to rise to 12.1 feet at the USGS river gage in North Chichester. Several properties were surrounded by floodwaters along Riverside Park Drive and Bachelder Road. Water was up to properties on Jasper Drive in Allenstown. Floodwaters encroached onto low lying properties of Kings Towne Park in Epsom.

Catastrophic flooding occurred across the Conway area on December 18th following heavy rain and snowmelt. The storm featured strong southeast winds measured between 30 to 55 mph in the region, which supported orographically enhanced rainfall and supported rapid snowmelt. The combined runoff from rain and snowmelt averaged 7 to 10 inches in the higher terrain, and 4 to 6 inches in the valley. The steep terrain and frozen ground supported rapid runoff which caused flash flooding along all streams and brooks in the region. The Swift River, a western tributary to the Saco River in Conway, was estimated to have had flows around 12-16 kcfs. The flows in the Saco River in Bartlett reached 24 kcfs. The annual chance occrrence of these flows are estimated around 1% to 0.2%, otherwise referred to as a 100 or 500 year flood. The combined flows in Conway resulted in flows over 60 kcfs as measured by the USGS gage. The stream height reached 17.72 on the evening of the 18th, exceeding the record held by Irene in 2011 which crested at 17.23 feet with a flow of 58.2 kcfs. The river climbed from 4 feet on the 17th to 17 feet in under 24 hours due to the rapid nature of the runoff.

Flooding and Damage was extensive with hundreds of residents impacted. The confluence of the Swift and Saco Rivers in North Conway drowned Washington St and shutting down both ends of West Side Road and preventing most traffic from getting in or out of the region. Over a dozen residents of Transvale Acres had to be rescued with 5 airlifted by helecopter from the National Guard. Homes in this community sustained severe damages with water several feet deep. Properties off Route 302 in Center Conway including Kenwood Circle, Robinwood Road, Burbank Road flooded with water several feet deep. Numerous campgrounds and recreational facilities including a golf course were completely inundated with water chest deep. The flooding continued along Route 113 River Street from Conway to Fryeburg.

Heavy rain and rapid snowmelt combined with steep terrain to produce rapid runoff. The resulting runoff over frozen ground caused flooding from the Rocky Branch River in Glen New Hampshire. The Stilling's Road became inundated and was closed due to the flooding.

Heavy rain and rapid snowmelt combined with steep terrain to produce rapid runoff. The resulting runoff over frozen ground caused numerous washouts and sinkholes along the Kancamagus Highway/NH Route 112. Flooding from the adjacent Swift River also eroded a 100 foot section just west of Conway.

Heavy rain and rapid snowmelt combined with steep terrain to produce rapid runoff. The resulting runoff over frozen ground caused flash flooding on the Ammonoosuc River causing a closure of the Tunnel Brook Bridge in Easton.

Heavy rain and rapid snowmelt combined with steep terrain to produce rapid runoff. The resulting runoff over frozen ground caused NH-25 at Elijah Beede Road and Elijah Craig Road in Sandwich to be closed due to flooding from the Meadow Brook.

Heavy rain and rapid snowmelt combined with steep terrain to produce rapid runoff. The resulting runoff over frozen ground caused flooding and the closure of Route 26 between Errol and the Maine stateline.

Heavy rain and rapid snowmelt combined with hilly terrain to produce rapid runoff. The resulting runoff over frozen ground caused washouts on Stokes, George, Braley and Butternut Ridge Roads in Hebron. North Shore Road from Gray Rocks Road to Cross Road flooded by the Cockermouth River. The Cockermouth River crested at 9.75 based on the USGS river gage located upstream of Hebron. This was 1.5 feet less than that reached following Irene in 2011.

Heavy rain and rapid snowmelt combined with steep terrain to produce rapid runoff and overtopping of the Campton Pond Dam which caused activation of the Emergency Operation Plan and the evacuation of homes as an abundance of caution. The dam did not fail and functioned as designed. The high flows did cause the Mad River to flood NH-49 in Campton downstream of the dam.

Heavy rain and rapid snowmelt combined with steep terrain to produce rapid runoff. The resulting runoff over frozen ground caused NH-116 from Paine Road to NH-112 in Easton to close due to flash flooding from Judd Brook.

Heavy rain and rapid snowmelt combined with steep terrain to produce rapid runoff. The resulting runoff over frozen ground cause numerous washouts and sinkholes along Route 302, along with a rockslide near Willey House. All lanes were closed from mile 43.6 to 55.8 in Crawford Notch.

Heavy rain combined with snowmelt caused significant runoff from the Presidential Mountain Range including portions of the Androscoggin River in Gorham. Thanks in part to dam controls on this portion of the Androscoggin River, the river only reached minor flood stage. The river gage at Gorham cresting at 8.7 feet on the 19th. However, further downstream from Shelburne to Bethel the flooding was major due to additional contributions from the surrounding mountains. In Gorham, the river flooded parking lots of businesses on Main Street. A combination of the Androscoggin River, Moose River, Moose Brook, and Peabody Rivers caused severe flooding of the Androscoggin Valley Country Club grounds. In Shelburne, several roads were flooded including US Route 2 at Route 16 and North Road. North Road flooded up to Philbrook Farm Inn between Meadow Road and Larry Brook Road. In addition, the bridge was flooded by the Shelburne Dam. Upriver the flooding was limited to Berlin City's Pollution Control Plant which sustained damage to pipes releasing effluent into the river.

Significant flooding occurred from Woodstock to Plymouth after a storm brought 3 to 6 inches of combined rain and snow melt to the region. The heaviest rainfall and most significant snowmelt water contribution occurred across the higher terrain of the watershed, where up to 10 inches of combined rainfall and snowmelt was released into the Pemigewasset basin. This caused the river to rise to its third highest crest at Woodstock, and 10th highest on record at Plymouth. This was also the highest crest on the Pemigewasset since Tropical Storm Irene in 2011. Estimates near the start of the watershed put the flow in the 1.0 to 0.5% chance of exceedance levels, also referred to as a 100-200 year flood event. It was less significant downstream however, with estimated flows at Woodstock being more consistent with a 25-50 year, and flows at Plymouth being more consistent with a 25 year event. The decreasing recurrence interval timeframe with downstream progress on the river highlights the significant role the higher rainfall amounts and snowmelt factored in near the top of the watershed, while relatively less input with decreasing elevation resulted in a tapering in the relative significance of the event. Damage was widespread along the Pemigewasset between Woodstock to Ashland. In the town of Holderness, up to two feet of water entered homes and local businesses on Avery Street, South River St, and North River St. Individuals that declined to evacuate were stuck in their homes as floodwaters entered during the early morning hours on the 19th. Water levels rose to the edge of the Plymouth State University Ice Arena doors. Numerous road closures were reported along Route 3, with up to five feet of water covering the roadways in Plymouth and Campton. Water up to two feet deep covered Route 3 in Thornton, and flooded numerous trailers and campers at local riverside campgrounds. Anecdotally, locals reported that the water levels in Thornton were higher than they were during Irene.

The Piscataquog River reached moderate flood stage on December 18th following heavy rains. The river came out of banks in the Danis Park Road community in Goffstown, cutting off access to some homes.

Rapid runoff from Bear Mountain caused Clark Brook to flood portions of Bristol to Hebron to Alexandria, including Gove Road. King Road after Burns Hill Road was washed out caused by excessive run-off from higher terrain in the region.