NOTE: Stream diversion management to improve water quality in a Connecticut water supply reservoir

Abstract

Managing raw water quality in drinking water reservoirs with the goal of reducing treatment costs and producing high quality finished water can involve a number of watershed and in-lake based approaches. Some water supply impoundment systems have structural controls that can vary the timing of water diversion from one or more subwatersheds. Water from approximately 77% of the watershed for the South Central Connecticut Regional Water Authority's (SCCRWA) Lake Saltonstall reservoir is accessed through a man-made diversion on the Farm River in East Haven, Connecticut. Watershed land uses include cropland, dairy farms and urban–suburban development. Operational data for the Farm River diversion indicate that water was diverted to the reservoir for 54% of the period from 1993 through 2002 and for 21% of the period that followed from 2003 through 2008. From 2001 through 2008, routine monitoring of reservoir water quality exhibited improving trends in Secchi depth, turbidity, chlorophyll a, color and total phosphorus. The measurable improvement in reservoir water quality seems to have resulted from active management of the stream diversion, which includes avoiding use during storm flows or when water system storage is safely above levels needed to meet customer demands. The benefits of this strategy for public water supplies are evident, but there are both positive and negative potential implications for instream flow management. Balancing multiple and often competing factors associated with water supply management requires the ability to implement operational practices that are both flexible and responsive.