Lake Water Levels : How & Why
Fall Lake Drawdown @ Oct 17, 2022 This year the Board of Selectmen are doing a staged drawdown--not immediately pulling the boards back to 30." The slower drawdown should help minimize erosion along the Lake shorefront and ameliorate damage downstream to Partridge Brook, which has had little flow through most of the summer due to drought conditions. The boards are currently set at 18" and will be dropped to 24" this week and 30" for the final drawdown next week. The Lake should be fully drawn down under this schedule in early November, well before ice settles in. There may be adjustments to the drawdown schedule dependent on weather conditions. Is Spofford Lake a variable level lake? Yes. 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. The Board of Selectmen is responsible for setting Spofford Lake’s water levels. The Summer water level is 716 feet 10 inches or 14 inches below the spillway abutment. The Winter/Off-Season is 715 feet 6 inches or 30" below the spillway 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 the water level chosen? In 2002, after consulting DES, the Board of Selectmen and Chesterfield residents agreed to a Summer water level of 716 feet 10 inches. Is this the “right “water level for Spofford Lake? To answer this, consider the following:
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.” Page updated on October 1, 2021 |
 | Spofford Lake Association PO Box 177 |