History Helping Hydrology in the Quinebaug River Study

In 1998 and 1999, federal and state environmental regulators issued water and wastewater permits for an evaporative-cooled combined-cycle gas-fired power plant. The plant is sited on a tributary of the Quinebaug River, which flows through Massachusetts and Connecticut, into the Thames River eventually discharging into Block Island Sound. One permit condition was to study ways to mitigate potential impacts to the river during low-flow periods. An analysis of historic U.S. Geological Survey (USGS) gauge records indicated that the median daily August flows, Aug Q₅₀, were higher before the construction of three U.S. Army corps of Engineers (ACOE) flood control/recreation lakes in the early 1960s. Because the Aug Q₅₀ was less after the lakes were built, the regulatory community hypothesized that lake evaporation was the cause. This paper examines this and alternative hypotheses and explains the cause of the change in streamflow regime.