When land is converted from its natural state to other uses, especially urban land uses such as roads, homes, and shopping centers, many impervious or paved surfaces are created. Rainfall can no longer soak into the ground. Instead it becomes stormwater or runoff.
As land is developed the volume, speed of flow, and pollutant loading of runoff increases. To minimize downstream flooding and protect lives and property, and to reduce pollution of water bodies, stormwater management practices are used to retain, detain and/or filter the runoff.
WHAT IS A SWALE?
Swales are one of the most commonly used stormwater practices. For many years they have been used along rural highways and residential streets to convey runoff. Today, swales not only convey stormwater but also help to treat runoff to reduce pollutants.
Like ditches, swales collect stormwater from roads, driveways, parking lots and other hard surfaces.
Unlike ditches, swales are not deep with straight sides. They have gently sloping sides and are wider than they are deep. They are vegetated to prevent the slopes from eroding and to help filter pollutants during and after rainstorm.
WHY ARE SWALES IMPORTANT?
Because swales are wider than they are deep (usually a 6:1 ratio), the rainwater is spread over a broader area. This slows the water and allows the runoff to temporarily pond.
Reducing the water’s speed allows the vegetation to filter the rainwater and remove sediments, heavy metals and hydrocarbons such as oil and grease.
Ponding of runoff in the swale allows the water to soak into the soil, helping to reduce the volume and amount of pollutants.
The gradual sloping sides of the swale make them easier to maintain and vegetate. This decreases erosion that causes sedimentation of streams, lakes and wetlands.
Swales or raised driveway culverts sometimes are used to promote ponding of runoff in the swale, especially when the swale has a steep slope. Swales or check dams can be made of soil, wood, or concrete.
HOW CAN YOU REDUCE POLLUTED RUNOFF?
MAINTAIN YOUR SWALE
Mow the swale but be careful to not damage swale blocks.
Remove and then compost leaves and grass clippings.
Keep good grass growth.
Minimize use of fertilizers, pesticides, and herbicides.
Aerate soils to restore percolation rate
DO NOT MISUSE YOUR SWALES
Do not pile garbage, trash, leaves, limbs or garden debris in swales – this add pollutants which can wash into downstream water.
Do not pave the swale – this reduces percolation of runoff.
Do not park vehicles in the swale – this compacts the soil so less runoff soak in.
LET THE WATER POND
Runoff should temporarily pond in the swale for 24 to 36 hours.
Don’t damage or remove swale blocks or check dams.
Don’t increase driveway culvert sizes.
ADD SWALES TO YOUR YARD
Waterfront property owners should build a swale and berm system to intercept runoff and pollutants from their yard.
Swales can be used between lots and at the rear of lots to intercept and retain runoff.
Swales can be used on residential and commercial land uses to collect roof runoff….
A berm is a mound of earthen materials made to serve a specific purpose.
Berms are among the oldest constructions made by man and have been used for centuries to contain areas, provide privacy and add variation to a landscape.
Berms can be landscaped with grasses and trees for a stunning focal point on your property. Some green designers will surround a home with a berm to blend it in with the environment.
Creating a berm is a beautiful and money-saving device for recycling excavated dirt. Dump fees for dirt removal can be very expensive and your land expert should suggest the creation of a berm.
It is important to use plants that will emphasize the berm’s form. If using a number of trees, plant them across or along the berm in a pattern that will accentuate its form.
If there is turf along with woody or herbaceous plants, the turf should be placed to allow for easy maneuverability while mowing. Generally, shrubs should be planted in masses that move gracefully around or across the berms. Any edging between turf and mulched areas should also consider the berm’s form.
Berms also make lovely sites for rock gardens, unusual groundcovers and dwarf varieties of common nursery plants.
It is also possible to incorporate plant materials that vary in height and style. Taller grasses can be planted on the backside of a berm with shorter varieties and perennials planted on the top and cascading part way down the front and sides. On the lower front and sides smaller more delicate plants can be installed where they will be noticed and appreciated most.
A well thought-out and constructed berm will bring interest to your site and is a wonderful option for solving a variety of issues in the residential landscape. Enjoy!
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