Lake Water Levels : How & Why

At what level will Spofford Lake be set in the Spring of 2021?

In 2021, the starting level is set at 716 feet 10 inches as per a decision by the Board of Selectmen, who are responsible for setting and maintaining Spofford Lake’s water level.  

(Subsequent to the initial setting of the boards, a board (s) was removed due to an abundance of rain.)

How is the Spofford Lake's water level computed?

Spofford Lake’s water level is controlled by a spillway or dam on Canal Road.  The top right corner of the concrete abutment of the spillway is 718' above sea level. At the agreed upon summer water level of 716 feet 10 inches, lake level is 14" below the top of the abutment.  

How is the Lake water level managed?

This is done by placing and removing 3 inch wide boards in the dam thereby increasing or reducing water flow from the Lake into Partridge Brook and then into the Connecticut River. 

Managing reasonable lake levels is a bit of a balancing act and guessing game involving a number of factors, e.g., the lake level at the time of ice out, the amount of snow runoff and the amount of Spring rain and its runoff.

Because there is only one point of outflow, i.e., the dam, lake levels cannot be quickly lowered when there is an abundance of rain. 

How was this water level chosen?

In 2002, after consulting DES, the Board of Selectmen and Chesterfield residents agreed to a summer water level 716 feet 10 inches.

Is this the “right “water level for Spofford Lake?

To answer this, consider the following: 

• The Lake has been dammed for 200 years and at 716'10" is more that 4 feet above its 'Natural Mean High Water” (see below) elevation of 712'.5."
• The 2020 Paleolimnology (Core Sediment) Report concludes that the Lake's oxygen impairment problem is largely caused by decaying organic matter eroded from the Lake's shoreline. 
• The Report also found that the rate of sedimentation in the Lake since 1910, and again since 1980, is the highest of any period over the past 500 years. 

What's the history of the Lake's water level over the past 100 years? 

• A dam (spillway) was built around 1919 with the top right corner set at 716 feet, rather than the current 718 feet.  At that time, the water level was set at 715' or approximately two feet lower than today.
• Reports circa 1955 indicate the Lake level standard was around 716’6”.
• In 1998, engineering studies done for a new spillway referenced 716’6” as the normal lake level.

If the water level has been at 716' 10'' for 20 years, hasn't the shoreline already eroded to this level?

No, old, compacted soils, rich in organic material, might take many decades to erode before a new “hardened’ shoreline is formed.  

Are water levels the only cause of erosion? 

Erosion naturally occurs from wind and rainfall.  However, today's watercraft, with ever larger engines, can create man-made erosion in the form of waves with magnitudes greater than those of 50 years ago. These 'artificial' waves crashing on the shoreline accelerate erosion.  Also, jet skis and tubers operating too close to the shoreline further accelerate erosion.

If 716'10" is too high, why don't we lower the Lake? 

For 20 years or more, property owners and boaters have come to believe that 716'10" is the Lake's  'normal/natural' water level. 

What is “Natural Mean High Water” (NMHW)?  

In July 2013, T.F. Bernier Report, a report commissioned by the NH DOT concluded that:

"Spofford Lake has been raised by damming for 200 years. Water elevation from that time until the late 1950’s fluctuated far more than similar natural lakes. The demand for lake water for use as a power source became so significant it resulted in a Supreme Court action in 1894. Even after water ceased to be used as a power source, complaints about low water in the lake continued as the town used the lake to flush sewage from Partridge Brook.”

"A conservative assessment of all of the physical and record evidence sets the Natural Mean High Water elevation at 712.5 feet of elevation in the North American Vertical Datum of 1988". 

Page updated on April 19, 2021