Mill River, Massachusetts

Project #1

Instream Flow Requirements of the Mill River, Hatfield MA

Sponsored by the Massachusetts Executive Office of Environmental Affairs, The Nature Conservancy, and the Massachusetts Environmental Trust

Status: Completed

The Mill River is a small tributary of the Connecticut River, on the western edge of the Connecticut River Valley in western Massachusetts. The main stem of the Mill River is a low gradient warm water stream, winding through fairly flat topography and is strongly influenced by interaction with groundwater flowing through the surrounding wetlands. In contrast, cold upland tributary streams drain the hilly topography to the west. The Mill River invertebrate community includes 9 species of freshwater mussels, including 3 state-listed species and the endangered dwarf wedgemussel. The unusual richness of the mussel fauna in the Mill River is a good indication that, despite historic use of the river and its tributaries for water supply, the native ecosystem is substantially intact. However, growing demand for future water use on two tributaries - West Brook and Roaring Brook - may alter the timing, duration, and intensity of flow and the related biological and water-quality characteristics of the river. Additionally, potential removal of the Hatfield Dam, near the confluence with the Connecticut River, may alter the faunal composition of the Mill River. This project was a joint effort of the NY and MA Cooperative Research Units - the first phase of a larger effort to develop a simplified method to evaluate instream flow requirements for streams in the northeast US. It aimed to quantitatively evaluate the ecological consequences of changes in river flow in the Mill River and affected tributaries as well as the removal of the Hatfield Dam. The project was composed of two complementary studies that described the physical habitat for fish communities and the dwarf wedgemussel community in the main stem of the Mill River.

Click below to read the final reports:

Instream Flow Requirements of Mill River - Dwarf Wedgemussel Habitat Final Report

• Appendix 1
• Appendix 2
• Appendix 3

Measuring River Ecosystem Health in Western Massachusetts - The Mill River, Hatfield, MA

• Appendix 1
• Appendix 2
• Appendix 3
• Appendix 4

Project #2

Feasibility Study of Removal of the Hatfield Dam, Mill River, Hatfield MA

Sponsored by NOAA and the US Fish and Wildlife Service

Status: Current

The historic Hatfield Dam (also known as the Advocate Dam) is located in Hatfield, Massachusetts near the mouth of the Mill River. It was built upon a 7 ft high sandstone outcrop. The concrete spillway built on this outcrop is 10 ft high and 120 ft long. This dam, the only one on the Mill River, blocks the movement of fish (Atlantic salmon, American shad, blueback herring and lamprey) and other aquatic organisms between the Connecticut River and the Mill River watershed. The tributaries to the Mill River, however, appear to contain ideal spawning and nursery habitat for Atlantic salmon. The discovery of a nesting salmon downstream of the dam further suggests that the fish might be available to establish a run at this system. A recent inspection of the dam by the Massachusetts Office of Dam Safety has rated this dam as at risk of failure, raising the possibility of dam removal for the sake of public safety as well as river restoration.

Dam removal at the site is complicated by a number of factors. The Mill River watershed is considered important due to the large diversity of freshwater mussels, including the federally endangered dwarf wedgemussel, that reside in the river and its tributaries. Removal of the dam could negatively impact that mussel population through the introduction of predatory species. It could also potentially impact the extensive upstream wetland system through a decrease in water levels. Therefore, a project team has been assembled to examine the feasibility and potential impact, of river restoration through removal of the Hatfield Dam or other design alternatives that help restore one or more ecological functions of the river. In addition, the old mill site was listed on the National Register of Historic Places in 1982.

The issues of dam removal and how it will impact river ecosystems are not confined to the Mill River. As part of a proactive effort to protect this valuable ecosystem and its many rare and endangered species, we are developing new approaches for evaluating the environmental costs and benefits of dam removal and for identifying ecologically-based stream flow requirements that can be used elsewhere in the Connecticut River watershed and throughout the state.

Click here to read the final report: Advocate Dam Removal Feasibility

Appendicies