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New Hampshire Department of Environmental Services

Winnipesaukee River Watershed

Smith River ID: BRSN3 Winnipesaukee River ID: TLTN3 Silver Lake ID: SLLNH Winnisquam Lake ID: LWINH Lakeport Dam ID: LKPN3 Opechee Bay ID: OPBNH Lake Winnipesaukee ID: WEIN3 Poorfarm Brook ID: POON3 Wolfeboro ID: WLFNH Shannon Brook ID: SHAN3 Winnipesaukee Map

Current Watershed Operations Information
Lake Winnipesaukee Year-to-Date Graph and Data

General Operating Constraints:

We are constrained to release a minimum of 250 cfs throughout the summer months to 
fulfill the following obligations and limiting restraints:

   1. Hydroelectric plants downstream of the lake have permanent deeded rights to 
      an outflow or 250 cfs in the river.  These historical water rights were 
      established in the 19th century but are still valid today.
   2. The State maintains water user contracts to other hydroelectric power 
      producers downstream.  These contracts are based on the presumption the State 
      will continue with the practice of maintaining the 250 cfs release rate.  
      Investment in the plants and long term operational expenditures in the plants 
      are based on this implicit understanding.
   3. The NH Fish and Game Department has requested a minimum runoff in the 
      Winnipesaukee River based on a runoff rate per square mile.  The runoff rate 
      they have requested is 0.5 cubic feet per second per square mile.  The 
      Winnipesaukee basin at the outlet from Silver Lake is 458 square miles, so 
      the rate they would like to see would be 229 cfs, close to what we are bound 
      to supply the hydropower companies.
   4. Silver Lake does not have a dam at its outlet, so that the discharge capacity 
      of the natural channel downstream from the lake controls the lake level.  At 
      below 250 cfs flow through the system, Silver Lake’s water level drops very 
      low, below that which is usable for many of the residents.
   5. Any significant reduction in summertime flow releases at Lakeport would 
      affect flow in the Merrimack River and reduce the capacity of the river to 
      assimilate pollutants. The 250 cfs release rate from Lake Winnipesaukee 
      augments low flows downstream during drought conditions.  Records from the 
      Merrimack River gauging stations, which reflect the historical releases at 
      Lakeport Dam, are used in NHDES permit limit calculations. From an NPDES 
      permitting perspective, it is important flow release at Lakeport Dam because 
      permits issued to wastewater treatment facilities and industries that discharge 
      to the Merrimack River include effluent limitations that are based on 7Q10 low 
      flow conditions in the Merrimack River.  New Hampshire wastewater treatment 
      facilities that discharge to the Merrimack River include the Winnipesaukee 
      River Basin Program in Franklin, the Merrimack County Complex in Boscawen, 
      and wastewater facilities in Penacook, Concord, Allenstown, Hooksett, 
      Manchester, Derry, Merrimack and Nashua.

List of constraints limiting the ability to maintain a higher lake level:

   1. When the ground  is saturated after multiple storm events or in the spring, 
      an inch of rainfall can bring up Lake Winnipesaukee by over 5 inches.  Due 
      to this it is imprudent to allow the lake level to rise above full lake level 
      for long periods. 
   2. Because the water level in the lake drops so significantly over the summer 
      season as outlined above, many residents’ docks are built at around the 
      average summer water level, not at full lake.  During the early summer when 
      the water level is high this can be problematic as wave action will surge and 
      pop boards off of docks as the waves pass. 

List of constraints limiting the ability to maintain a lower lake level:

   1. The deeded release rate listed above along with significant summer 
      evaporation results in a drop of the lake level by approximately 15 inches 
      throughout the summer months. The evaporation rate alone removes water at a 
      rate approximately equal to the 250 cfs release rate at the dam.  Every 250 
      cfs drops the lake level by 0.01’ per day, so with evaporation and no rainfall 
      the lake can be expected to drop 0.02’ or about a quarter inch per day. 
      Historically there is a lack of offsetting runoff in the lake summer months 
      so that the only source of water available to maintain the lake level is water 
      stored from the spring runoff.  
      In anticipation of this drop throughout the summer, a starting summer target 
      elevation is set for Lake Winnipesaukee of 504.32’ to allow for enough water 
      to be able to keep the lake as close to usable level as possible at the end 
      of the summer and into the early fall.
   2. Early in the summer there are years Lake Winnipesaukee begins the summer 
      season high.  Hydropower producers have limited ability to pass large volumes 
      of water, the maximum rate being 750 cfs at one facility.  In order to utilize 
      this source of energy efforts are made to limit the discharge rate from the 
      lake to match this value.  Other sites can use up to 1100 cfs, and this is also 
      used as a target discharge rate when the lake is too high and efforts are made 
      to lower it by releasing water.     
   3. High release rates of water can cause shoreline damage, and many complaints 
      arise even during flooding conditions when it is imperative to drop the lake 
      levels by releasing more water.  This is particularly true in the springtime, 
      when ice sheets moved by rapidly moving water can damage structures along the 
      shore.  An effort is made to weigh the offsetting sources of damage, high water 
      vs. rapidly moving water against the shoreline corresponding to high flow 

The information contained on this page, as well as on the links presented on the 
map above, is intended to provide data and information relative to ongoing 
meteorological conditions and associated operating decisions as implemented by the 
New Hampshire Department of Environmental Services (DES) within the referenced 
watershed. Although the data presented herein is intended to be an accurate 
representation of actual conditions, it is presented for informational purposes only 
and the user is cautioned to use it at his/her own risk.
Related Information

NH Department of Environmental Services | 29 Hazen Drive | PO Box 95 | Concord, NH 03302-0095
(603) 271-3503 | TDD Access: Relay NH 1-800-735-2964 | Hours: M-F, 8am-4pm

copyright 2008. State of New Hampshire