Lake Drawdown
An annual drawdown of 3ft is utilized at Onota Lake to protect against flooding during spring runoff, protect against shoreline destruction from ice, and to provide limited control of invasive species. During the reconstruction of the Onota Lake dam in 1995, the 4-foot diameter outlet pipe previously in place was replaced with a 2-foot diameter pipe. This, inevitably, reduced the maximum outlet flow to twenty-five percent (25%) of the previous capacity, making it difficult to achieve drawdown within the ideal timeframe and climate. This problem was corrected in 2011 when a second two-foot diameter outlet pipe was added to the dam, restoring most of the original capacity.
Drawdown is a potentially effective means of controlling nuisance aquatic species within shallow areas of Onota Lake. Since nuisance plants such as E. watermilfoil, and Curlyleaf Pondweed are most problematic in shallower areas, this management technique may be particularly effective for the control of nuisance plants. An annual drawdown of 4 ft would be expected to reduce milfoil and curly-leaf pondweed cover over 257 acres of the lake. A drawdown of 8ft would be expected to increase the aquatic plant management area to over 324 acres of the total coverage area. (Wagner, 1996) The LOPA Drawdown Committee reviewed lake bathymetry and existing data in 2003. The committee estimated that an annual drawdown of 6ft would approximately double the aquatic plant management area and recommended periodic deep drawdowns. The City of Pittsfield has, for the past decade, followed a plan of yearly 3-foot drawdowns interspersed with targeted deeper drawdowns of 5.5-6 feet every 3 years. The city is currently preparing a new notice of intent to obtain a new permit to replace the current permit which expires at the end of 2018.
