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How does ground water pumping affect streamflow?

Nov. 19, 2012 – The United States Geological Survey has released a new report about the effects of ground water pumping on surface
water.

Nov. 19, 2012 – Ground water provides drinking water for millions of Americans and is
the primary source of water to irrigate cropland in many of the nations
most productive agricultural settings. Although the benefits of
ground water development are many, ground water pumping can reduce the
flow of water in connected streams and rivers – a process called
streamflow depletion by wells. The United States Geological Survey (USGS) has released a new report that
summarizes the body of knowledge on streamflow depletion, highlights
common misconceptions, and presents new concepts to help water managers
and others understand the effects of ground water pumping on surface
water.

"Ground water discharge is a critical part of flow in most
streams–and the more we pump below the ground, the more we deplete
water flowing down the stream," said USGS Director Marcia McNutt in a press release. "When
viewed over the long term, it is one big zero-sum game." 

Ground water and surface-water systems are connected, and ground water
discharge is often a substantial component of the total flow of a
stream. In many areas of the country, pumping wells capture ground water
that would otherwise discharge to connected streams, rivers, and other
surface-water bodies. Ground water pumping can also draw streamflow into
connected aquifers where pumping rates are relatively large or where the
locations of pumping are relatively close to a stream.

"Streamflow depletion caused by pumping is an important
water-resource management issue across the nation because of the adverse
effects that reduced flows can have on aquatic ecosystems, the
availability of surface water, and the quality and aesthetic value of
streams and rivers," said Paul Barlow, USGS hydrologist and author on
the report. "Managing the effects of streamflow depletion by wells is
challenging, particularly because of the significant time delays that
often occur between when pumping begins and when the effects of that
pumping are realized in nearby streams. This report will help managers
understand the many factors that control the timing, rates, and
locations of streamflow depletion caused by pumping."

Major conclusions from the report:

• Individual wells may have little effect on streamflow depletion, but
  small effects of many wells pumping within a basin can combine to
  produce substantial effects on streamflow and aquatic habitats.

• Basinwide ground water development typically occurs over a period of
  several decades, and the resulting cumulative effects on streamflow
  depletion may not be fully realized for years.

• Streamflow depletion continues for some time after pumping stops
  because it takes time for a ground water system to recover from the
  previous pumping stress. In some aquifers, maximum rates of streamflow
  depletion may occur long after pumping stops, and full recovery of the
  ground water system may take decades to centuries.

• Streamflow depletion can affect water quality in the stream or in
  the aquifer. For example, in many areas, ground water discharge cools
  stream temperatures in the summer and warms stream temperatures in the
  winter, providing a suitable year-round habitat for fish. Reductions in
  ground water discharge to streams caused by pumping can degrade habitat
  by warming stream temperatures during the summer and cooling stream
  temperatures during the winter.

• The major factors that affect the timing of streamflow depletion are
  the distance from the well to the stream and the properties and
  geologic structure of the aquifer.

• Sustainable rates of ground water pumping near streams do not depend
  on the rates at which ground water systems are naturally replenished (or
  recharged), but on the total flow rates of the streams and the amount of
  reduced streamflow that a community or regulatory authority is willing
  to accept.

"Conjunctive management of ground water and surface-water resources is
critical in New Mexico, where our limited surface-water supplies can be
impacted by new uses that are predominantly dependent on ground water
pumping," said Mike Johnson, chief of the hydrology bureau in the New
Mexico office of the state engineer. "This new USGS publication
consolidates our understanding of the connection between aquifers and
streams and provides a clear, thorough and up-to-date explanation of the
tools and techniques used to evaluate streamflow depletion by wells."

The report, which is a product of the USGS Groundwater Resources
Program, is titled Streamflow Depletion by Wells – Understanding and
Managing the Effects of Groundwater Pumping on Streamflow, and is
available in print and online.