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What
does Stormwater Management have to do with you...?
Hinckston
Run Watershed Fact Sheet (pdf format)
| It happens when it rains…someone's
street floods…someone's basement gets wet - and someone calls their municipality
to ask what's being done. Summer brings more calls: concerns about wells
or streams drying up. Municipalities and residents are asking the question,
"What can be done?" |
| The runoff is generated
from impervious surfaces like roads, rooftops and parking lots, which also
prevent rainfall from soaking into the ground. Increased runoff means more
flooding. Decreased infiltration means less groundwater for wells and streams.
Without the use of BMP's around the home, basements flood. The problems
are all connected! |
| Not so long ago, the predominant
philosophy of stormwater control focused on flood control and directing
water off an individual piece of property as quickly as possible.
As towns grew, curbs, gutters, trenches, and pipes assisted the land use
and stormwater planner alike in meeting this goal. While this turned out
to be a successful strategy for individual properties, the additive effects
of runoff from these individual properties on a watershed scale contributed
to flooding and water quality problems. This has led water quality professionals
to rethink stormwater control. This is the reason each township and municipality
must have set up what is called "Stormwater Best Management Practices"
(BMP). |
| BMP's are used to reduce
runoff, improve water quality and encourage infiltration to protect our
environment. Compliance with federal, state, and local stormwater programs
revolves around the use of “Best Management Practices,” or BMPs, to manage
stormwater. |
| There are a list of ways
to reduce problems and control stormwater. Each control method has its
pro's and cons. Non are infallible used alone but used in conjunction with
one another can create a strong BMP system for the entire township. This
in turn creates good benefits for each individual property. |
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| 1- Naturalized Basins-
One of many new methods to help alleviate some of these traditional stormwater
problems is to naturalize existing stormwater basins. The goal of naturalizing
existing stormwater basins is to maintain the overall design of the basin
while increasing environmental, aesthetic and economic benefits. A naturalized
stormwater basin is one that is attractively landscaped, incorporating
native trees, shrubs and wildflowers. |
| Naturalized basins tend
to have vegetation that requires only annual mowing. By decreasing maintenance
costs your tax dollars can be diverted to more important township services. |
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| 2-Bioretention Islands-
Bioretention islands are designed to use soil and plant material to mimic
natural processes. The vegetation, mulch layer, planting bed and drainage
materials store, filter and infiltrate storm water. This improves water
quality in areas that generate a variety of pollutants, such as parking
lots. In contrast to traditional parking lot islands, bioretention islands
are recessed. The pavement is graded to these areas, where storm water
is captured and treated. Considerations: Suitable for
use in sites with drainage areas smaller than 5 acres and preferably less
than 1 acre. |
3-Wet Lands or Wet Ponds-
Wet ponds (a.k.a. stormwater ponds, retention ponds, wet extended detention
ponds) are constructed basins that have a permanent pool
of water throughout the
year (or at least throughout the wet season) and differ from constructed
wetlands primarily in having a greater average depth. Wet ponds are among
the most widely used stormwater practices. While there are several different
versions of the wet pond design, the most common modification is the extended
detention wet pond, where storage is provided above the permanent pool
in order to detain stormwater runoff and promote settling. Advantages:
If properly designed, constructed and maintained, wet basins can provide
substantial aesthetic/recreational value and wildlife and wetlands habitat.
Ponds are often viewed as a public amenity when integrated into a park
setting. Disadvantage: Some concern about safety when constructed
where there is public access. |
| 4- Porous Pavement-
Porous pavement is a special type of pavement that allows rain and snowmelt
to pass through it, thereby reducing the runoff from a site and surrounding
areas. In addition, porous pavement filters some pollutants from the runoff
if maintained. There are two types of porous pavement: porous asphalt and
pervious concrete. The biggest disadvantage for use: Can
only be used for lightly used access roads. |
| 5- Retrofit Stormwater
Basin -Converting a conventional detention basin into Vegetated Water
Quality Basin. A vegetated water quality basin or an extended detention
basin is a BMP designed to (1) maximize the flow path through the basin,
(2) slow the flow of stormwater through the basin, (3) improve how plants
use stormwater to increase absorption and evapotranspiration, (4) filter
and trap common runoff pollutants, (5) promote soil saturation/groundwater
recharge, and (6) increase evaporation of stormwater. Basin conversions
generally involve removing concrete low-flow channels, modifying outlet
structures so basins hold water from small storms, re-grading to modify
flow path, and re-vegetating with native species. |
| 6- Riparian Buffers-
Riparian buffers are vegetated zones adjacent to streams and wetlands that
represent a best management practice (BMP) for controlling nitrogen entering
water bodies. Current research indicates that riparian buffers of various
vegetation types are effective at reducing nitrogen levels in groundwater
and streams. Buffer width is only one factor controlling nitrogen removal
effectiveness. Subsurface removal of nitrogen in riparian buffers is often
high, especially where conditions promote microbial denitrification. Riparian
buffers are a single component of comprehensive watershed management plans,
which must also include point source and non-point source control of nitrogen.
Creating ordinances and zoning to protect existing buffers will likely
be cheaper than creating new buffers or restoring degraded ones. However,
restoring buffers may be a necessary component of watershed water quality
protection. |
| 7- Vegetated Swales
- A vegetated swale is a broad, shallow channel with a dense stand of vegetation
covering the side slopes and bottom. Swales can be natural or manmade,
and are designed to trap particulate pollutants (suspended solids and trace
metals), promote infiltration, and reduce the flow velocity of storm water
runoff. Vegetated swales can serve as part of a storm water drainage system
and can replace curbs, gutters and storm sewer systems. Therefore, swales
are best suited for residential, industrial, and commercial areas with
low flow and smaller populations.
Disadvantage: Vegetated
swales are typically ineffective in, and vulnerable to, large storms, because
high-velocity flows can erode the vegetated cover. |
| 8- Sediment Forebays-
A small basin or cell within the basin separated by a berm or barrier near
the inlet to trap and filter sediment and debris first entering the basin.
This forebay is designed to permit sediment and pollutants to drop out.
The berm can be constructed of earth or riprap. Forebays should be vegetated. |
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Did You Know?
...
Traditional stormwater management
focuses on rate control while largely ignoring the quantity and
quality of stormwater runoff that enters our creeks. |
| Traditional stormwater management
methods have resulted in water quality and flooding problems that have
degraded our rivers, streams, and lakes. Problems such as water pollution,
stream bank erosion, dry streambeds, and reduced aquifer recharge, are
some consequences of poorly managed stormwater. |
| Stormwater best management
practices (BMPs) can help reverse these trends and restore our streams. |
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| A Note About Mosquitoes: |
| An extended detention basin
and rain garden planted with a variety of wet meadow plants provides better
treatment of stormwater and poses less of a mosquito problem than a basin
planted with turf grass because frogs, dragonflies, and birds that will
thrive in a wetland meadow ecosystem will act as natural controls. |
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NOTES ABOUT PLANTINGS
IN BASINS
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| A LANDSCAPE PLAN.
The landscape plan to be developed should consider soil and moisture conditions.
When using vegetative BMPs, select plant species with consideration to
their moisture tolerance. Locate native plants well adapted to wet conditions
in areas inundated by stormwater and plants tolerant of dry conditions
in higher areas less often exposed to stormwater. |
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| MANAGING YOUR VEGETATION.
Plantings in a vegetated extended detention basin and on basin slopes perform
a valuable function; however, woody vegetation growing too near basin structures,
such as an outlet or inlet pipe, can impact basin function and lead to
costly maintenance. Invasive plants, such as Phragmites and Japanese Knotweed,
should be controlled since they can out-compete desirable native plants.
Managing vegetation to protect facility integrity includes performing a
periodic inspection and as-needed maintenance to control invasive plants
and remove woody debris. |
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| WOODY WASTES.
While grass clippings and small amounts of leafy plant matter can remain
in the basin to naturally decompose, it is recommended that large amounts
of plant debris, particularly woody stems and branches, be removed to ensure
stormwater flow through the basin is unimpeded. |
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| For more information on
native plants and a list of recommended plants, please visit the following
web sites: Pa
Dept of Conservation and Recreation &
Pa Native Plant Society. |
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