Tara Lamper: Historic dam be damned?

People in the small town of Alton are in an uproar. A big change is on the horizon, and there are a multitude of concerns.

Conveniently central to most destinations around the state, from mountains to coast and amenities in between, Alton is a quaint, rural village that becomes a busy tourist town in summer. It sits at the southern tip of Lake Winnipesaukee, with the Merrymeeting River winding through the community and opening into Alton Bay. Waterfront living and recreation is a significant portion of revenue for the town.

Near the northern end of the Merrymeeting River is the old Alton Power Dam. Constructed in 1923 and rehabilitated in 1979, it originally served as a hydroelectric generation plant. Today, it serves only to hold back recreational water in Wentworth and Mill Ponds. These small bodies of water provide the community with popular fishing spots, a seasonal ice skating rink, and scenic views. The area around these ponds holds incredible biodiversity. According to forester Tom Foster, one tiny fragment of land near the dam is identified as supporting over 70 species of plants. Mill Pond also acts as catchment for runoff from the town center, preventing or reducing pollution from flowing into Lake Winnipesaukee.

The Alton Power Dam, owned by New Hampshire Fish & Game and operated by the NH Department of Environmental Services Dam Bureau, is classified as a high hazard dam with risk for failure during a “1,000 year storm event,” which could wipe out Letter S Road and surrounding low-lying residences. Although the dam has held throughout many high-water events over the past century, including recent catastrophic flooding that washed out Route 140 and the fatal 1996 collapse of Meadow Pond Dam, it fails current safety requirements. The cost to fully repair the dam is currently considered prohibitive by the Dam Bureau.

Due to these safety and budgetary concerns, Fish & Game and NHDES plan to decommission and likely remove the dam after gathering more information about what the impacts would be and the total cost of removal. This process will begin after ice-out in late March of this year, ultimately drawing down the water level by 2.5 feet.

According to NHDES, the drawdown will be performed by removing a maximum of one six-inch stoplog per day, monitoring impact with each step. The Dam Bureau states that this phased release reduces the risk of sediment erosion and potential for movement of contaminants. The timing of an ice-out drawdown is strategic to minimize the disturbance of overwintering amphibians and nesting waterfowl.

During and following the drawdown, the Dam Bureau will conduct water and sediment testing to assess quality and contamination levels. They will also monitor any impact on connected waterways, flora and fauna. Observations and test results will be compared to existing baseline samples before proceeding as the state deems appropriate. There is currently no schedule set for the next stage of dam removal or remediation, which is likely five or more years off.

The Alton Conservation Commission, in cooperation with other local environmental groups, has begun their own water sampling as well to ensure full awareness of any possible environmental and infrastructural impacts. ACC will continue testing and monitoring throughout the drawdown process.

Potential mobilization of contaminated sediment is the most immediate concern. ACC suspects a large buildup of sediment behind the dam, which could be stirred up and washed downstream toward the bay during the drawdown or dam deconstruction. If this is proven true, remediation would be required before removing the dam or possibly even continuing with the drawdown. NHDES does not believe this will become an issue during drawdown as enough water depth should remain above the localized sediment to minimize disturbance.

Mill Pond, which connects to Wentworth Pond and will be affected by lowering water levels, is also known to be highly polluted. As Mill Pond will drain into Wentworth Pond at an unnatural rate during drawdown, there may be potential for additional contamination to enter the water system, whereas it currently sits mainly undisturbed. At this time, water testing of Wentworth Pond shows contaminated discharge from Mill Pond is minimally detected, likely due to the dilution effects of the flowing Merrymeeting River.

Aesthetic environmental impact is the next concern and one of the biggest public outcries. Lowering the water level will expose quite a bit of shoreline in these small ponds, which the community worries will become mudflats. While this is certainly possible to some extent, revegetation generally occurs within one season, the dormant seed banks within the soil quickly sprouting to life. However, invasive species are always a threat and may begin to colonize the newly exposed areas. Consequently, close monitoring of the regrowth process will be pertinent. 

The effects on the greater Merrymeeting River and marsh system are unknown and will largely depend on the topography of Wentworth Pond’s floor. If the drawdown’s impact reaches further upstream than expected, NHDES claims it will halt activities. Merrymeeting Marsh contains endangered species, among its other important functions, so all groups agree that it must be protected from any negative impact.

Worries about other impacts to the community, such as potential effects on ground water levels and nearby wells, the insulation of town water lines running under the river, and of course the effect on views and property values remain at the forefront of the public’s mind. Unfortunately, the Dam Bureau will not know the extent of these or the aforementioned impacts until they begin drawdown and subsequent monitoring.

On the flip side, dam removals also have positive impacts on the environment. In fact, studies have shown that manmade dams are ecologically disruptive. As The Nature Conservancy puts it, rivers are the arteries of the earth and dams create blockages. Free-flowing rivers allow proper distribution of sediment and nutrients, and greater migration of aquatic life. Meanwhile, unnaturally dammed ponds impede the passage of fish and other wildlife, and can create stagnation, leading to toxic algae blooms. (We see this in Mill Pond.) Connectivity supports biology and balance, whereas impoundments reduce biodiversity. In practically every case study of removed dams, the long-term environmental benefits far outweighed the immediate community impact.

Still, balance between environmental health and a town’s well-being must be considered. Obviously, a sudden change in the connectivity of the Merrymeeting River system after a century of being dammed might have unforeseen repercussions to both the local ecosystem and community. It is imperative that each step forward is taken with care, regarding all sides that may be affected.

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Tara Lamper is a member of the Alton Conservation Committee.