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Watershed Management Bureau
Coastal Program
Nonpoint Pollution Control Program
Land Use & Water Quality
Coastal Watershed Groundwater Resources Study
Growth and sprawl are the most common problems mentioned in New Hampshire’s
coastal communities today. From a water resources perspective, growth and
sprawl are significant because of the impacts that impervious surfaces have
on the water cycle.
Impervious surfaces include roads, parking lots, compacted earth, and all
other surfaces that prevent water from naturally infiltrating into the soil.
As our communities continue to develop, more and more of our natural environment
is converted to impervious surfaces.
By preventing water from infiltrating into the ground, impervious surfaces
create increased surface runoff. This runoff carries nonpoint pollutants
such as sediment, coliform bacteria, fertilizers, and oil and grease, directly
into receiving streams and water bodies. Impervious surfaces also change
the way that water cycles through our watersheds. Trees and vegetation lost
to development no longer intercept precipitation, and their water storage
capacity is lost. Groundwater recharge may be depleted or altered. Pipes
and engineered drainage systems move water quickly from developed areas to
receiving streams. Not only is more water removed from the watershed, but
it is removed more quickly. As a result, streams during and after a storm
must accommodate more water, which can lead to flooding, downcutting of streams,
and stream bank erosion. In addition, during drought conditions, there is
less groundwater to provide base flow to streams.
In 2000 a study was implemented by the New Hampshire Office of State Planning
(OSP) Coastal Program (NHCP) to assess the impacts of varying amounts of
impervious surfaces on water quality in three small basins of the coastal
region. This initial study had been followed by a joint USGS/OSP project
to assess the effects of urban development on water quality; and follows
to a limited degree, the approach taken by the United States Geological Survey
(USGS) assessing urbanization effects on water-quality in the Boston metropolitan
area; a number of the streams studied were in the New Hampshire coastal region.
The next phase of the study will build upon both the NHCP sampling program
and the USGS urban land-use gradient study to better define the water quality
effects from increasing urbanization.
Specific concerns are:
- What are the effects of various intensities of urban land-use on stream-water
quality?
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How do selected constituent concentrations vary with hydrologic conditions?
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What are the current conditions of macroinvertebrate communities and algal
biomass and how do these relate to nutrient concentrations and stream site
characteristics?
View the Final Report, of the first two years of study and
a Proposal for Additional Work, August 2002.
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