Low Flow Inventory

Weymouth and Weir River Basins\

Observations

Estimated pre-development baseflows for the Plymouth River in Hingham indicate that the River would run dry in September and October during dry years, but would flow year-round with normal or above average precipitation (2).

Suspected Causes

Bypassed Reaches / diversions The section of Accord Brook with the worst low flow problems is in Wompatuck State Park in Hingham. In this reach, water is diverted out of the streambed to recharge public water supply wells. This bypassed reach was dry from June to October in 1999 (3).

A unique bypass problem occurs as a result of the US Army Corps of Engineers' "deep rock tunnel" from Town Brook in Quincy to the Atlantic ocean. The tunnel was created to alleviate flooding problems downstream, but, unfortunately, also siphons away baseflows, causing chronic low flows over smelt-spawning habitat. These conditions have resulted in significant smelt egg kills and spawning habitat degradation over the last five years.

Low stream flow in Town Brook, Quincy (March 1998) Smelt egg kills caused by low flows (March 1998)

In addition to the dewatering caused by the deep rock tunnel, Town Brook also experiences frequent streamflow spikes, which cause additional stress to the aquatic community (4).

Stream flow data from Town Brook, Quincy showing extreme low flows in March 1998 that caused the smelt egg kill as well as frequent streamflow spikes.

Consequences

Aquatic Flora and Fauna Low flow problems in the Weir River and Accord Brook, one of its tributaries, were identified in the Weir River study. Pre-development stream flow for August was estimated to be 0.68 cfsm, but conditions in Accord Brook were 0.37 cfsm and in the Weir River 0.39 cfsm during the study. Baseflow was reduced by up to 62% in the Weir River, and Accord Brook currently dries completely.

The Weir River report developed minimum streamflow recommendations to satisfy human demands and maintain adequate habitat for selected river fish in the Weir River:

• 0.14 cfsm for June through October
• 1.07 cfsm for October through March
• 3.11 cfsm for March through May
• 1.36 cfsm for May through June.

Maintaining these minimum flows in the river would provide just 50% of the fish habitat that was available during low flow periods under “virgin”, pre-development conditions. The study also estimated that in order to maintain these seasonal minimum flows, a maximum of 2.7 mgd could be withdrawn from the Weir River Basin, as compared to the current 4.28 mgd that is withdrawn (4). A comparison of benthic macroinvertebrate communities in Crooked Meadow Brook, Hingham, and Accord Brook, Hingham, was made by DEP staff. Although Crooked Meadow Brook was estimated to run dry even under pre-developed conditions in the Weir River Report, its benthic macroinvertebrate community was composed of typical flowing water species. Accord Brook, on the other hand, was also inhabited by organisms typically associated with stagnant water and temporary streams (1).

References & Resources

1. Boston Harbor Basin 1999 Draft Water Quality Assessment Report. (Revised 1/12/01)
2. GZA Weir River study
3. Samantha Woods, Weir River Watershed Association. Personal communication, June 2002.
4. Hutchins, Eric. National Oceanic and Atmospheric Administration. Personal communication, March 2, 2004 and Brad Chase MA Division of Marine Fisheries. Personal communication, March 2004.