Lower Great Falls dam
Lower Great Falls
Lower Great Falls, also known as Somersworth Dam, is a captivating hydroelectric structure located in Rollinsford, New Hampshire. Completed in 1984, this concrete, gravity, and masonry dam stands at a height of 36 feet and spans 270 feet in length. With a storage capacity of 472 acre-feet and a maximum discharge of 8460 cubic feet per second, it plays a crucial role in managing the Salmon Falls River's flow and supporting the surrounding ecosystem.
Managed by the Federal Energy Regulatory Commission, Lower Great Falls is a state-regulated dam that undergoes regular inspections to ensure its structural integrity and operational efficiency. The dam features a controlled spillway with a width of 178 feet and is equipped with two slide (sluice gate) outlet gates. Its hazard potential is assessed as significant, indicating the importance of proactive risk management measures to mitigate potential dangers and ensure the safety of downstream communities.
With a risk assessment rating of very high, Lower Great Falls poses a critical focal point for water resource and climate enthusiasts. Its strategic location, impressive design, and vital role in hydroelectric power generation make it a significant landmark in the region. As efforts continue to monitor and maintain this essential infrastructure, it stands as a testament to human ingenuity in harnessing the power of water resources while respecting the natural environment.
Dam data reference
Condition Assessment
- Satisfactory
- No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
- Fair
- No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action.
- Poor
- A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency.
- Unsatisfactory
- A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
- Not Rated
- The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Hazard Potential Classification
- High
- Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
- Significant
- Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
- Low
- Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
- Undetermined
- Dams for which a downstream hazard potential has not been designated or is not provided.
Plan around the weather
Same NOAA / yr.no feed Snoflo's iOS app uses. Watch the precipitation column on the meteogram -- rain on the basin upstream typically lifts inflow 24-72 hours later.
Next 5 days, hour by hour
Temperature line with weather symbols on top, snow + rain accumulation as columns, humidity as a dotted line.
5-day forecast table
Every 3 hours, broken out across temperature, snow, rain, humidity, and wind. Each cell is colour-coded relative to the column min/max.
| Time | Condition | Temp (°F) | Snow (in) | Rain (in) | Humidity (%) | Wind (mps) | Wind dir |
|---|---|---|---|---|---|---|---|
| Loading detailed forecast… | |||||||
15-day temperature & precipitation
Daily temperatures, snow, and rain projected over the next two weeks.
Nearby streamflow gauges
USGS streamgauges around Lower Great Falls -- inflows here typically show up in storage 24-72 hours later.
| Streamgauge | Discharge | View |
|---|---|---|
| Isinglass R At Rochester Neck Rd | 53 cfs | → |
| Cocheco River Near Rochester | 97 cfs | → |
| Oyster River Near Durham | 11 cfs | → |
| Lamprey River Near Newmarket | 119 cfs | → |
| Mousam River Near West Kennebunk | 225 cfs | → |
| Winnicut River At Greenland | 17 cfs | → |
Make a day of it
Boat launches, lakeside camping, fishing access, and other reservoirs near Lower Great Falls .
Boat launches
- Salmon Falls River Boat Launch
- Willand Pond Boat Launch
- Dover Eliot Road South Berwick
- Cathy Schiro O'Brien Cross Country Running Trail Dover
- Oyster River Boat Launch
- Piscataqua River Boat Launch
Campgrounds
- Old Stage Campground
- Saddleback Campground
- Remote Campsite
- Tidewater Campground
- Green Tops Campground
- Ferry Beach Campground
Paddle runs
Track Lower Great Falls in the Snoflo app
Save this dam as a favorite and get the local NOAA / yr.no forecast plus regional flow context wherever you are.
About Lower Great Falls
Where does the data for Lower Great Falls come from?
Structural and regulatory data come from the U.S. Army Corps of Engineers' National Inventory of Dams (NID). Weather forecast comes from NOAA / yr.no -- the same feed Snoflo's iOS app uses.
How often is the report updated?
NID structural data refreshes annually as the Corps publishes updated assessments. The weather forecast refreshes throughout the day.
What does the Significant hazard rating mean?
The Corps of Engineers' hazard potential classification grades probable consequences if the dam fails: High = probable loss of human life; Significant = no probable loss of human life but possible economic loss / environmental damage; Low = no probable loss of human life, only minor economic / environmental losses. See the Dam Data Reference card above for the full definitions.
What's "% of normal"?
The current storage value compared to the historical average storage on this calendar day. 100% = right on average; values above 100% mean above-normal storage (wet year); values below mean below-normal (dry year or drought).
Can I get alerts when storage crosses a threshold?
Yes -- alerts are managed in the Snoflo iOS app. Favorite this dam, set a threshold, and you'll get a push the moment conditions cross.
Other water bodies near here
Snoflo-tracked reservoirs and dams within driving distance of Lower Great Falls .