Low Flow Inventory

Blackstone River Basin

Historical Perspective

The Blackstone River watershed has smaller amounts of stratified drift and wetlands than many other Massachusetts watersheds. Without significant stratified drift deposits and wetland areas, rainstorms tend to cause flashy rises in streamflow and baseflows tend to be low because there is less water storage capacity available in aquifers. Because of the naturally occurring low summer flows, people living in the Blackstone River Watershed have had to find creative ways to store water, particularly for summertime uses. Many impoundments were created historically to store water for water supply, mill operations, and boat passage, particularly during summer months. Between 1828 and 1848, the Blackstone Canal provided passenger and freight passage between Worcester and Providence, but recurring problems with low flows eventually led to its abandonment. There are even reports that during this time mill owners and canal operators sabotaged each other’s water control structures during disagreements over the equitable appropriation of streamflow.

Ironically, the Blackstone River mainstem may currently have more water in it than ever before. Interbasin transfers of water for the City of Worcester’s public water supply come from the Nashua and Chicopee River basins and are discharged as wastewater into the Blackstone River. In fact, so much of the summer baseflow of the Blackstone River is derived from wastewater discharges that there may not be enough clean river water for sufficient dilution of discharged pollutants in some sections.

Despite the flow augmentation from interbasin transfers, many sections of rivers and streams throughout the watershed suffer from unusually low streamflows due to human activities.

Observations

Many sources have reported unusual low or no-flow conditions throughout the Blackstone River Watershed. For example, Poor Farm Brook from City Farm Pond, Shrewsbury, to Lake Quinsigamond was observed dry during November of 1998 by the Blackstone Headwaters Coalition during a shoreline survey. In September of 2004, DEP and DFG staff observed no flow conditions in the same location, from City Farm Pond to Lake Quinsigamond (see photos below). The Town of Shrewsbury's Home Farm wellfield is located at the confluence of Poor Farm Brook and Lake Quinsigamond, and is a suspected cause of zero flow conditions.

Poor Farm Brook between City Farm Pond and Lake Quinsigamond, Shrewsbury, was dry on September 2, 2004

A DEP staff member reported no flow on the Quinsigamond River below Hovey Pond in North Grafton (6).

USGS Water Resource Investigations Report No. 93-4167 states that unnamed headwater tributaries crossing the Quinsigamond Aquifer near one of Shrewsbury’s town wellfields lose approximately 0.5 cubic feet per second to groundwater withdrawals and run dry if upstream flow is less than this (1). Local residents too, have noticed changes in streamflow patterns relatively recently. One local resident first noticed low flow problems on the Mumford River in the summer of 1999. These conditions returned in the summers of 2000 and 2001 and some sections of the river even ran dry during these periods (8). The Massachusetts Watershed Initiative funded a study of the causes of low flow incidents on the Mumford River.

Suspected Causes

The causes of low flow in watercourses of the Blackstone River Watershed are numerous. Although no comprehensive study has been conducted, ground and surface water withdrawals, hydropower generation, dam and reservoir operating procedures, operation of bypass structures, and increases in impervious surfaces related to development are some of the activities most likely to deplete streamflow.

Water Withdrawals

Groundwater withdrawals can have local effects individually and basin-wide effects when considered as a whole. The Massachusetts Water Resources Commission lists the Quinsigamond River as a high stress river based on its low discharge per square mile of watershed compared to other rivers in the state (2). The USGS Water-Resources Report, previously mentioned, also stated that the Auburn aquifer is completely developed and the Quinsigamond aquifer is almost completely developed. This suggests that future growth may lead to further problems with streamflow due to aquifer depletion unless new methods are developed to reduce demand for water.

In fact, the Department of Environmental Protection’s Blackstone River Basin 1998 Water Quality Assessment Report suggests further study of many cases where nearby water withdrawals may already deplete streamflows:

Streamside wells in the Town of Auburn may affect water levels in Dark Brook.

The Town of Shrewsbury’s well field near Poor Farm Brook may have exacerbated the low water levels that resulted in the brook drying up from City Farm Pond to Lake Quinsigamond in 1998.

Mill River and Peters River also had low flows which may be the result of nearby groundwater withdrawals.

In 2004, a DEP staff member observed Purgatory Brook in Sutton dry below Swans Pond with stagnant, non-flowing conditions upstream to the reservoir. Private irrigation wells and development within the watershed are the suspected causes of declining streamflows in Purgatory Brook. (17)

Dam Management

The Blackstone River and its tributaries also have many dams that serve different purposes and may contribute to low flow problems. Some of these dams are not actively managed or are run-of-river, but others are actively managed to produce power or store drinking water, for example. Reservoir operations on Kettle Brook in Leicester and the Holden Reservoir on Tatnuck Brook in Holden may create or exacerbate the low flow conditions that were observed by DEP staff downstream in 1998 (6). Kettle Brook was dry from Reservoir Number 1 in to Waite Pond, Leicester, in the summer of 1998. Maintenance and other operations at the Riverdale Mill hydropower facility on the Blackstone River in Northbridge and Uxbridge may also contribute to low flow conditions downstream (10). During periods of low flow, water can be withheld and released several times a day, causing fluctuations in river stage, aquatic habitat availability, and navigation downstream. It has been suggested that these fluctuations may also help to resuspend contaminated sediments in this reach.

Bypassed Reaches / Diversions

The Synergics Hydropower Project diverts the majority of streamflow in the Blackstone River around the Blackstone Gorge to its dam at the old Tupperware Mill in order to generate electricity. In effect, the entire Gorge is bypassed and flow is drastically reduced there. Similarly, flow on the Blackstone River essentially bypasses the Town of Worcester because its water supply withdrawals occur on two upstream tributaries, Kettle and Tatnuck Brooks to the northwest, but the discharge point is downstream on the Blackstone River mainstem. All the water that would have flowed from Kettle and Tatnuck Brooks through the Blackstone River in Worcester is discharged downstream (11).

Development

One study suggested that an increase in development and imperviousness in the Mumford River subwatershed was at least partially to blame for the increased duration of low flow events in the 1990’s. This study noted that low flow events were lower and longer in duration in the 1990’s than several decades earlier. In addition to low flow effects, high flows were more frequent, of greater magnitude, and in direct response to storm events, indicating that the flashiness of the river may have increased due to documented increases in development, particularly during the 1980’s, within the subwatershed (3).

Consequences

Aquatic Flora and Fauna

The Massachusetts Department of Environmental Protection conducted a biological assessment of Kettle Brook by comparing it to a reference river which represented the best possible attainable conditions (6). Streamflow on Kettle Brook was affected by reservoir operations on Kettle Brook Reservoir upstream which left large areas of substrate exposed. Staff found fewer pollution intolerant macroinvertebrates, such as mayflies, stoneflies, and caddisflies, and more pollution tolerant species, particularly chironomid midges, in Kettle Brook than in the reference river. The fish community was also unbalanced and had a low species richness when compared to the reference site. Although the water quality and aquatic habitat were good enough to support a healthy fish and macroinvertebrate community, low flows on Kettle Brook prevented many aquatic species from occupying all of the available space and thus limited the biological potential of the stream (6). For a stream like this, returning more normal water levels and seasonal variations may be all that is required for the aquatic community to recover and thrive.

Pollution

Low flow conditions themselves create other problems throughout the Blackstone River Watershed. In some headwaters of the Blackstone River, particularly above the wastewater treatment plant in Hopedale, existing pollution problems become worse during periods of extreme low flow (5). On the Mumford River, one local resident reported seeing juvenile trout with white, “marshmallow-like” growths on their heads, fins, and backs during a period of low flow when the fish were confined to a small pool below the sewage treatment plant (8).

References & Resources

1) Izbicki, John A. 2000. Water Resources of the Blackstone River Basin, Massachusetts. USGS Water-Resources Investigations Report 93-4167.
2) Stressed Basins in Massachusetts. Final draft, Office of Water Resources, version 3. December 2001.
3) Louis Berger Rhode Island, Inc. April 1, 1999. Preliminary Assessment of Causes of Increased Long Duration Low Flow Events in the Blackstone River.
4) Brian Duval, DEP Environmental Analyst, personal communication March 2002.
5) Glen Krevosky, personal communication January 2002.
6) Weinstein, Mollie J., Kennedy, Laurie E. and Jane Colonna-Romano. May 2001. Blackstone River Basin 1998 Water Quality Assessment Report. Commonwealth of Massachusetts Executive Office of Environmental Affairs, Massachusetts Department of Environmental Protection, Bureau of Resource Protection, Division of Watershed Management.
7) Mauri Pelto, Professor of Geology, Nichols College. personal communication January 2002.
8) Mike Yacino, Gun Owner’s Action League. personal communication January 2002.
9) Dan Meharg, National Park Service, Woonsocket, RI. Personal communication with Russ Cohen, MA Riverways Programs.
10) Russ Cohen, Massachusetts Riverways Programs, Department of Fish, Wildlife, and Environmental Law Enforcement. personal communication 2002.
11) USGS real-time stream gage data for the Blackstone River at Millbury.
12) USGS real-time stream gage data for the Blackstone River at Northbridge.
13) USGS real-time stream gage data for the Blackstone River at Woonsocket, RI.
14) USGS real-time stream gage data for the Quinsagamond River near North Grafton.
15) USGS real-time stream gage data for the West River below West Hill Dam near Uxbridge.
16) Blackstone Headwaters Hydrology Project, Professor Mauri Pelto, Nichols College
17) Beaudoin, Therese. DEP CERO. personal communication, July 2004.