Case Studies on Rivers with Low Flow

Ipswich River Case History
The Ipswich River watershed is 155 square miles, and includes all or part of 21 communities in northeastern Massachusetts. The topography of this Atlantic coastal plain basin is characterized by low relief, with an average grade of 3.1 feet per mile. The surficial geology of the region is primarily glacial till with stratified sand and gravel deposits covering about 43 percent of the basin and alluvial deposits covering about 3 percent of the basin.

This small river system supplies water to 330,000 people and thousands of businesses in 14 communities, providing all or part of the public water supply for 14 communities including Beverly, Danvers, Hamilton, Ipswich, Lynn, Lynnfield, Middleton, North Reading, Peabody, Reading, Salem, Topsfield, Wenham, and Wilmington. In 2001 approximately 12 billion gallons of water were withdrawn for public water supplies.

In 1997, the Ipswich River was listed as one of the nation's most threatened rivers because of its severe low-flow problems. Much of the upper half of the river dried up or was reduced to isolated stagnant pools in the summers of 1995, 1997, and 1999. In 1999, the river experienced record low -flows in May, June, July and August.

In early 2000, the United States Geological Survey completed the development of a model of the hydrology of the Ipswich watershed that documented the magnitude of the impact of these water withdrawals on low flows in the Ipswich River. The USGS found that groundwater withdrawals in the upper reaches of the watershed are the main factor reducing summer flows by up to 90 percent. The diversion of wastewater to treatment plants outside the watershed also significantly reduces flow.

A companion study by USGS and the Massachusetts Division of Fisheries and Wildlife found that the Ipswich River's fisheries have been seriously degraded by low-flow problems. The river's biodiversity has been diminished, with the loss of most "river dependent" species. The study identified several management objectives needed to restore the river to health. A fisheries restoration task force is completing work on recommendations to restore healthy fisheries to the Ipswich River.

Additional info can be found at www.ipswichriver.org.

Assabet River Case History

Conditions in the Assabet River Watershed

Although the mainstem of the Assabet River will never lack for flow while the four major wastewater treatment plants that line its banks discharge treated sewage effluent to the river. But flow alone will not make clear sailing - or canoeing as the case may be - for the Assabet River. During summer low-flow periods as much as 80% of the flow measured at the USGS gage in Maynard (two thirds of the way down the river) is treated effluent and the entire length of the river is overwhelmed with nutrients. The excess nutrients cause severe eutrophication (overgrowth of nuisance weeds). In the summer the impounded sections of the river can be completely choked floating mats of duckweed and masses of rooted weeds under the surface.

As a result, the river does not meet Massachusetts water quality standards and the state is conducting a study (a nutrient Total Maximum Daily Loading study) of the river to determine the clean up needed to meet those standards. The work to date shows that the river is nutrient saturated, and that the four municipal wastewater treatment plants contribute the lion's share of the nutrient load to the Assabet. It is now clear to all who have been following this issue that a dramatic reduction in nutrients discharged to the river from these plants must be part of any plan to restore the Assabet. For any nutrient load reductions to be effective, the watershed's existing baseflow - the underground flow from aquifers to streams - must be preserved and where possible, restored.

The route to restoring baseflow is "keeping water local." The Assabet watershed as a whole is considered a "net importer" of water - this means more water enters the watershed than leaves it on any given day, because some of the Assabet communities get their water from the Quabbin reservoir. However, the flow of water within the Assabet watershed tells a less appealing story. When clean water is pumped from the aquifers underlying the subwatersheds (tributary basins), and sent to the Assabet mainstem in the form of sewage effluent, the Assabet's water quality suffers, small streams lose water, and the aquifers are not replenished. The resulting damage to the hydrologic cycle can have long-term damaging consequences for wildlife and humans, harming habitat and endangering future water supply.

OAR's Work in the Assabet River Watershed

Since its founding in 1986 the Organization for the Assabet River has worked to protect, preserve and enhance the natural features of the Assabet River, its watershed and its tributaries. Recognizing that the protection of baseflow is vital to the health of the river, OAR:

• seeks a better understanding of the watershed's hydrology through our own StreamWatch program (see below) or by advocating for hydrologic studies such as the current USGS hydrologic study
• advocates for baseflow protection by commenting on Water Management requests
• encourages stormwater recharge projects in the watershed

Starting in the summer of 2002, the Organization for the Assabet River (OAR), as a part of the new StreamWatch project team, will be measuring and reporting streamflow and water quality, and habitat quality in the tributaries of the Assabet River to assess habitat conditions for native fish. StreamWatch is a cooperative project of OAR, USGS, the MA Division of Fisheries and Wildlife, Mass Audubon, and the Assabet River Consortium funded by a grant from US EPA. The goals of the project are to raise awareness of the tributary streams of the Assabet River, provide the public with accurate, timely information, and influence water conservation and management decisions to protect the ecological integrity of the watershed.

Assabet Watershed Description

The Assabet River watershed is approximately 20 miles west of Boston, Massachusetts; the river arises at the swamp-like A1 impoundment in Westborough and flows northeast 31 miles to its confluence with the Concord River in Concord. The Assabet River drains a watershed of approximately 177 square miles, and has a population of about 177,000 people. The river flows through several highly populated areas including Westborough, Northborough, Hudson, Maynard, and Concord. A large proportion of the water supply in the watershed comes from wells in the shallow, stratified drift aquifers near the Assabet River and its tributaries. Four major and three minor wastewater treatment plants (WWTPs) discharge treated effluent to the river.