Read about NepRWA's
Water
BUDGETS Project
(Balancing
Uses with Demands to Generate Effective Techniques for
Sustainability)
How
much water does a healthy river need?
The Neponset River Watershed has experienced dramatic
improvements in water quality since the implementation of
the Clean Water Act of 1972. Unfortunately, streamflow, or
water quantity, has not received as much attention, and it
has become an issue of critical concern as communities
continue to seek additional sources of water supply.
How
does water move in a natural system?
Water is a finite resource that is continually recycled and
transported by the water cycle. The sun's energy drives this
cycle. Water moves into the atmosphere through evaporation
and plant transpiration, or evapotranspiration.
The atmospheric vapor is transported by wind, condensed into
clouds, and then returned to earth as precipitation. It is
estimated that every 9-12 days, all moisture in the
atmosphere falls to the earth, making water our most
recycled resource
How
do we affect streamflow?
Today the Neponset
River Basin plays a key role in providing low cost, high
quality drinking water to residents of the watershed.
Residents of Canton, Dedham, Foxboro, Medfield,
Sharon, Walpole, Westwood and Stoughton get some or all of
their drinking water from the Neponset basin.
This water comes not from reservoirs or other surface
water sources, but from groundwater.
Groundwater
is stored between grains of soil and rock, just beneath the
earth’s surface.
An aquifer is an area under the ground with a lot of
available space between soil particles and rock. Water
can occupy this total space. Throughout the watershed, the massive glaciers that once
forced their way over the landscape, thousands of years ago,
have left their mark in aquifers of glacial stratified
drift, porous deposits of sand and gravel that overlie more
than half of the river basin.
In some parts, this layer is more than 150 feet
thick! It is
estimated that the basin can store more than 95 billion
gallons of water. Furthermore,
the quality of much of this water is excellent.
Several test wells in the unused northern part of
Fowl Meadow are of such high quality that they would require
no treatment before drinking.
Despite the quantity and quality of groundwater in the
Neponset watershed, these resources are very fragile.
Much of this water is held in a large “unified”
aquifer stretching 200 feet below the surface which allows
contaminants to spread from one area to another in much the
same way that pollution would spread from one end of a lake
to the other. The
threat to these resources is compounded by the fact that the
large aquifer is shared and managed by more than one town.
Already eight municipal wells have been closed due to
contamination. Furthermore,
the quality of groundwater in some other areas has been
reduced by run off from roads and other non-point sources.
Besides, the threat of contamination, over use now endangers
the groundwater resource of the Neponset basin.
As the population within the Neponset River Watershed
grows, increasing water withdrawals adds more stress to the
river, creating a severe problem of low flow during hot
summer months and drought years.
The Massachusetts Water Resources Authority (MWRA) sewer and
water system service most of the 14 communities of the
Neponset Watershed. When
the vast majority of people in the Neponset Basin take a
shower, do their laundry or flush their toilet, the
resulting wastewater flows into the MWRA sewer system which
carries it out to Deer Island for treatment and disposes of
it in the Boston Harbor.
The creation of this sewer system has been a blessing for
water quality in the watershed, providing communities with a
simple means of disposing of their waste without
contaminating the river.
As with all environmental issues, however, there is a
trade-off.
More than 200,000 people in the Neponset Watershed get their
water not from the Quabbin Reservoir, but from local wells.
Every time these communities turn on the tap, they
draw water out of the underground aquifers, which feed the
Neponset River and dump it into the sewer system, which
takes it directly to Deer Island.
It has been conservatively estimated that the volume
of water lost each year from the Neponset River to outside
basins now exceeds 20% of the river’s total annual
freshwater discharge.
At the same time that this “interbasin transfer” is
increasingly contributing to low river flows, new impervious
surfaces such as driveways, parking lots, and roofs are
reducing the amount of water recharged to the Neponset’s
aquifers. When rain falls on the Neponset River Watershed, it is
absorbed by the ground as groundwater.
This groundwater feeds the massive underground
aquifers, which in turn feed into the Neponset River.
As more open space is developed into houses, roads
and other impervious surfaces, rainwater, which used to soak
into the ground, now must run off. This results in higher streamflows during floods, but reduces
the amount of groundwater storage available to naturally
recharge streamflow and drinking water supplies during dry
periods. The
result is higher flood flows, but lower drought flows.
A lack of adequate water flow in rivers and streams,
especially during the late summer, can be just as damaging
to the health of the river as poor water quality. Low flows contribute to hotter water temperatures, as water
sits for longer periods in lakes and ponds, and decreased
oxygen levels for aquatic life.
If water levels drop too much, fish eggs can be
exposed to the air and dried out, and wetland plants adapted
to high water levels can die off reducing habitats for birds
and other animals. In
some situations, low flows can exacerbate poor water
quality, because there is less water available to dilute
pollutants.
A variety of human activities impact streamflow, they
include: Consumptive water use, or inefficient use of water
for both indoor and outdoor household uses. These uses
increase in the summer as more people water their lawns,
wash their cars, and fill their swimming pools. Impervious
surfaces, or paved areas such as parking lots and roads.
Impervious surfaces cause rainwater to runoff into streams
and lakes, rather than allowing it to soak into the ground
and recharge underground aquifers. Interbasin transfer,
which occurs when water is withdrawn from one watershed and
wastewater is disposed of in a different watershed. Many
Neponset Watershed communities withdraw drinking water from
local aquifers, but they dispose of wastewater in
Massachusetts Bay via the centralized MWRA sewer system and
Deer Island.
You can make a difference in protecting Neponset River
streamflows by conserving water in your home and practicing
low water lawn care techniques.
Click here to learn
more.
