Originally built to power the mills along the Winnipesaukee and Merrimack Rivers, today powering downstream hydropower plants is one of many needs the dam fills. Learn more about the complexities of balancing these competing interests and the importance of lake level management to water quality.
Under deeded water rights that date back to the 1800’s, hydropower dams on the Winnipesaukee River are entitled to a minimum release of 250 cubic feet per second (cfs), which is equal to 112,208 gallons per minute from the dam.
However, in addition to fulfilling deeded obligations, this minimum release from Lakeport Dam also helps meet the needs for the fisheries in the Winnipesaukee River, provides a desirable water level in Silver Lake downstream in Belmont and Tilton, and allows the Winnipesaukee River Basin Program Wastewater Treatment Plant in Franklin meet its permit requirements for its discharge into the Winnipesaukee River.
Also, under state statute, the downstream hydropower plants on the Winnipesaukee and Merrimack Rivers pay Water User Fees for the storage and release of water at Lake Winnipesaukee, which fund the operation and maintenance of the dam. Therefore, when other factors allow, the needs of these hydropower plants are considered when making decisions about the amount of water to be released from the dam.
To meet the recreation interests on the lake, the dam is operated to try to have the lake full, at elevation 504.32 feet, by the end of May, the beginning of the summer recreation season.
Water levels much above full can cause problems with boating, preventing access to marinas in Wolfeboro and Alton and creating a greater potential for shoreline erosion. Water levels much below full can also cause problems with boating for the owners of property where the waterfront depth is shallow.
However, it is difficult to maintain a constant water level on Lake Winnipesaukee. When the soil is saturated from previous rain storms, an inch of rain over the 363-square-mile watershed that flows into Lake Winnipesaukee will raise the lake level five inches.
Also, from the beginning of June to the beginning of September, the lake level will, on average, drop approximately 10 inches due to evaporation and the 250 cfs minimum release made from the dam during the summer.
To provide for some protection against floods, the lake level is lowered in the fall up to two feet below its summer full level to help control the typically high spring runoff that occurs from snowmelt and rainfall in the months of March and April.
However, when the lake is full during flood events, a balance must be struck between high lake levels and high flows in the Winnipesaukee River downstream, both of which can be significantly damaging. During these events, inflows into Lake Winnipesaukee can peak at rates between 8,000 and 10,000 cfs, but if flows the Winnipesaukee River exceed 2,000 cfs they start to cause flooding to low-lying properties downstream.
Added to these concerns are operational constraints associated with protecting the important fish and wildlife resources. For example, the lake trout that make Lake Winnipesaukee their home spawn right around Halloween each year.
Therefore, it is important that the lake level does not fall much below the level it is at on Halloween to avoid stranding the eggs. This can limit the amount of storage that can be provided to help control the heavy spring runoff.
Likewise, loons, which are protected by state law and by federal regulations as a migratory bird, return to the lake in the spring, establish their nests close to the shoreline, and must have relatively stable lake levels through May and June to avoid flooding or stranding of their nests. This can result in water releases from the dam that may be higher than desirable to prevent flooding of the nests.
Also, releases need to be closely managed from the middle of August to the middle of November to avoid damage to American eels who migrate out of the dam on the way to the sea during this period.
A fuller explanation of the operational objectives and constraints in managing the lake level of Lake Winnipesaukee can be found on the website for the New Hampshire Department of Environmental Services.
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