Gulf Brook at low streamflow

Managing Streamflow: Low Flow and Flooding

Too much water leads to flooding, and too little water leads to low flow in our streams. Both extremes have a negative impact on our water quality and the wildlife that lives in our waterways. Heavy precipitation and periods of drought cannot be controlled, but NRWA does work to minimize human impacts on streamflow.

Low Flow

When precipitation is low and evapotranspiration reduces the amount of water in a stream, cool groundwater replenishes the stream and helps to sustain fish and other aquatic life through periods of drought-like conditions. However, other demands on groundwater can reduce the amount of water available to maintain healthy streamflow to rivers and streams. Water withdrawals from municipal drinking water wells, lawn watering, agriculture and other types of irrigation, and commercial and industrial uses reduce the water available. If the quantity of water withdrawn exceeds the amount of water replenished through precipitation and groundwater recharge, the result is a dry or low flow stream with decreased oxygen and raised water temperatures that stresses or kills fish and other aquatic life.

NRWA works to protect against the issues of low flow through projects that are in keeping with our Sustainable Water Use Policy, such as our Water Monitoring Program where volunteers track streamside conditions; through working with communities, state agencies and other environmental groups to encourage sustainable water policies; and through our education programs for adults on subjects such as Low Water Use Landscaping.


In contrast to water withdrawals, impervious surfaces, such as asphalt roadways and parking lots, expanses of cement, and roof tops cause a rapid increase in flow to streams during heavy rainstorms or rapid snowmelts. This fast flow makes the streams rise quickly or be “flashy” and does not allow rainwater to infiltrate slowly back into the ground to replenish groundwater. Streams that receive water runoff quickly from impervious surfaces are prone to flooding, especially in urban areas. Rapid runoff not only causes flooding but also carries pollutants and sediment into our waterways, such as road oils, salt, sand, and yard chemicals.

Nashua River at the Pepperell dam during 2010 flood - Photo by Pam GilfillanNRWA works to protect against rapid runoff by helping developers and municipalities address the issue through good stormwater management and low impact development and other Smart Growth planning. The NRWA works with municipal Public Works personnel to discuss local stream quality and the impact of their road management practices. And we collaborate with Conservation Commissions, government agencies, and other organizations to protect wetland areas that serve as sponges absorbing large volumes of water during periods of excess precipitation. Our Purple Loosestrife Management Project is focused on helping to control this invasive species that threatens to take over natural wetlands ecosystems.

For more information on streamflow and NRWA water projects, please contact Martha Morgan, NRWA Water Programs Director, at (978) 448-0299, or email This email address is being protected from spambots. You need JavaScript enabled to view it..