Low Flows & Floods

Low Flows

Despite our location in the relatively wet northeast, the Ipswich River is one of the most flow stressed rivers in the United States. In 1997 the Ipswich River was designated as one of the “20 Most Threatened Rivers in America”, by American Rivers. In 2003 that designation was upgraded to one of the “10 Most Endangered Rivers in America” due to worsening flow conditions.

Town Forest Pool September 2005. Reading.

Water withdrawals for drinking water are the major cause of low and no flow conditions in the Ipswich River, according to studies by the United States Geological Survey (USGS). In recent years communities with water supply sources in the Ipswich watershed used an average of about 40 million gallons of water per day. About two thirds of this water comes directly from the Ipswich River or wells within the Ipswich watershed.

While public water supply withdrawals are the most significant cause of the river drying up, another issue is waste water, whether from septic systems, stormwater or groundwater leaks, that enter sewer systems and is pumped outside the watershed. The USGS studies found that diversions of waste water out of the upper reaches of the Ipswich watershed significantly contribute to low flow conditions.

The rapid pace of development in some portions of the watershed has created more impervious surfaces such as pavement and buildings. Stormwater is not able to soak into the soil and recharge underground aquifers, resulting in increased flooding during rain storms and decreased flow in dry periods. Techniques to improve water filtering into the ground during and after storm events (rather than running off paved surfaces) are being tested in the Ipswich River and at our headquarters in Ipswich, Riverbend.

Consider these trends:

  • In the late 1800’s, before the first sewers were built in Ipswich River communities, most of the water withdrawn from the watershed was returned as wastewater to the basin. In 2002, it is estimated that about 80% of the total wastewater produced in the basin (about 8.8 billion gallons per year) is exported out of the basin.
  • The Ipswich River’s all-time low-flow record of 0.1 cubic feet per second, set in 1957, was tied or broken on 18 days in 1997, with a new low of 0.05 cubic feet per second being set in September of 1997. That record was broken in 2002, with a new extreme of 0.04 cubic feet per second.
  • On average, water use doubles (or worse) in many communities in the Ipswich River Watershed in summer. This means that the most water is used when the River’s flows are naturally lowest.
  • Primarily due to low flows, almost 50% of the native river fish species have been eliminated from the river, or greatly reduced in numbers.

The municipal lot in Ipswich, May 2006


The way we live on the land may make natural events like floods more extreme. The loss of wetlands leaves less area to soak up and store the rain.

Development changes drainage patterns, flooding basements that didn’t previously have water problems. Paved surfaces like roads, parking lots and buildings are impervious to rainwater. So instead of slowly percolating into the ground, the water rushes off these hard surfaces into our streams and rivers.

The flip side of all this runoff is that less water is stored in the ground. This becomes a problem in the summer, when households consume more water from the Ipswich River and its connected groundwater aquifers to irrigate lawns.

The “too much or too little” water problem is only growing worse. The four most severe floods ever experienced in the Ipswich River have occurred in the past twenty years.

Howlett Brook at Topsfield Road Flooded

During May 2006 flooding, Howlett Brook submerged portions of Ipswich Road in Topsfield, upstream of Willowdale State Forest. Peak flows measured at USGS gaging stations on the Ipswich River were the highest recorded since data collection began in the 1930s. (Photo: L. Manzi)

What can we do? We can build our homes and communities in ways that maintain the natural hydrology, so that rain can slowly percolate into the ground and recharge the river. We can retrofit existing developments, and new developments can be compact and clustered around existing downtown areas, and preserve remaining forests and wetlands. We can use “low impact development” techniques like rain gardens, porous pavement and constructed wetlands to infiltrate rain into the ground where it falls. Green roofs can minimize runoff and reduce energy costs too. We can minimize lawn area, avoid over-irrigating, and use native plants to create beautiful natural landscapes. Learn more about the Greenscapes North Shore program.