Water Withdrawals

Water withdrawals come in two varieties, surface and groundwater:
(Both types of water withdrawals can seriously reduce flow in streams and rivers.)

• In surface water withdrawals, water is taken directly from a river, stream or lake.

  Surface water withdrawals usually involve the use of reservoirs. Instead of taking water directly from a river or stream, a reservoir is built to capture and store a large volume of water for use. Reservoirs may be built by building dams directly across rivers and streams, or they may be located away from the river or stream. When located away from rivers or streams, they are typically filled by pumping water from a nearby river or stream into the reservoir.

  Typically, reservoirs operate by capturing large volumes of water during months when flow levels in rivers and steams is high, and saving it for use when needed. Thus, most reservoirs go through an annual pattern of filling in winter and spring, when flow is high and water use is relatively low, and emptying in summer when flow is low and water use is high. Reservoirs constructed by building dams across rivers or streams often are required to release a certain amount of water to maintain flow downstream during the summer months. If people use too much water during the summer, there may be little or no water left to release to maintain flow below the reservoir.

• groundwater withdrawals are made by installing wells and pumping water from beneath the surface of the earth.

  Groundwater withdrawals are frequently even more damaging to rivers and streams than surface water withdrawals. This is because the large wells that are used to provide municipal water supplies are typically located close to streams and rivers. When located along rivers and streams, these wells intercept water that would otherwise provide flow. This is usually not a problem during the winter and spring months when flows in rivers and streams is naturally high.

  In summer and early fall, when flow in Massachusetts rivers and streams is typically at it lowest annual levels, however, these wells may capture most or all of the available water, leaving little or none left in the river or stream. This problem has recently been documented in detail in the Ipswich River, where municipal wells have been found to reduce summer flows by as much as 90%.

Large water withdrawals in Massachusetts are regulated under the Water Management Act.