Low Flow Inventory

Connecticut River Basin

Suspected Causes

Water Withdrawals Six public water supplies withdraw water from the Mill River subwatershed upstream of Hatfield. Water withdrawals from reservoirs on West Brook and Roaring Brook within the Mill River subwatershed leave downstream sections of the stream beds dry during low flow periods. The Town of South Deerfield is also under an Administrative Consent Order from the DEP to study the impacts of a possible increase in its permitted withdrawal amount on the river (1). Currently, the New York and Massachusetts Cooperative Research Units are studying instream flow requirements for the Mill River as part of “... a larger effort to develop a simplified method to evaluate instream flow requirements for streams in the Northeast US” (2).

Dam Management The flow fluctuations on the Connecticut River at the hydropower dam in Holyoke can be seen at the USGS real-time website for the Holyoke stream gage. Rapid daily fluctuations for power generation, often referred to as "hydropeaking", can cause scour, erosion, and downstream sedimentation problems as well as stranding aquatic organisms from eggs to adults in isolated pools or on dry land.

Bypassed Reaches / Diversions The Connecticut River is diverted at Turner Falls dam into the Northeast Utility’s canal and used to generate hydropower. Two miles of the river below Turners Falls dam are bypassed and are virtually dry during low flow periods. During low flow periods, the plant operates as a hydropeaking plant and returns water to the Connecticut River at Cabot Station. During high flows, the plant operates as a base load plant and water is returned to the river over the Montague dam as well. The Federal Energy Regulatory Commission (FERC) requires a continuous minimum flow of 1,433 cfs or an amount equal to the inflow from the river and higher releases are made during the fish migration season (1).

Consequences

Aquatic Flora and Fauna The dam on the Mill River in Hatfield limits the distribution of state and federally listed freshwater mussels including the alewife floater (Anondonta implicata) and triangle floater (Alasmidonta undulata). However, it also protects the dwarf wedgemussel (Alasmidonta heterodon) from predatory fish that would prey on tessellated darters (Etheostoma olmstedi), a species that helps the dwarf wedgemussel reproduce successfully. The Hatfield dam has been rated in poor condition by the Massachusetts Dam Safety group at the Department of Environmental Management and studies are currently underway to investigate possible alternatives for streamflow management here (1).

Current Events

The Connecticut River Joint Commissions, a collaboration of citizens and state and federal representatives, produced the Connecticut River Corridor Management Plan in 1997, which includes a section about Flow Management and Dams. Suggestions from this collaborative process included: maintaining water flows at levels which will support the full range of its uses and values, coordinating inter-state policies on flow management and water withdrawals, cooperative flow management among tributary and mainstem dam owners, integrated flow control systems, and sharing of flow management expertise among dam operators (3).

References & Resources

1. Weinstein, Mollie J. and Laurie E. Kennedy. November 2000. Connecticut River Basin 1998 Water Quality Assessment Report, Report Number 34-AC-1, DWM Control Number 45.0. MA DEP, Bureau of Resource Protection, Division of Watershed Management.
2. Cornell University’s Instream Habitat Program, Mill River Project Description.
3. Connecticut River Joint Commissions. May 1997. Connecticut River Corridor Management Plan: Volume 1 Riverwide Overview, Upper Connecticut River in New Hampshire and Vermont.
4. Hanover, Kathy Fallon. April, 1998. Instream Flow Uses, Values & Policies in the Upper Connecticut River Watershed. A report to the Connecticut River Joint Commissions.
   includes policy and site-specific information and recommendations for the Vermont/New Hampshire section of the Connecticut River .
5. USGS real-time stream gage on the Connecticut River at Montague City.
6. USGS real-time stream gage on the Connecticut River below the hydropower dam at Holyoke.
7. USGS real-time stream gage data for the Mill River at Northampton.