Swale Systems

Why manage runoff?

When a land area is developed from a natural state to other uses, especially urban land uses such as roads, homes or shopping centers, much impervious or paved surfaces are created. Thus, causing a situation (environment) not conducive to allow rainfall to soak into the ground (percolation). This process of percolation, promotes the breaking-down of pollutants and slows the flow of runoff before allowing the water to return to groundwater sources or to flow into the local environmentally sensitive waters of Boca Ciega Bay and/or the Gulf of Mexico. Instead, the rainfall strikes the land and begins to flow. Thus, becoming stormwater runoff. As land is further developed, the volume, speed or flow, and pollutant loading of runoff increases. To minimize downstream flooding, protect lives and property and to reduce the pollution reaching our water bodies, stormwater management practices should be used to retain, detain, and/or filter the runoff.

Runoff Protection and The Introduction of Swales

Swales are one of the most commonly used stormwater practices. For many years swales have been used along rural highways and residential streets for the purpose of conveying runoff. Today, swales not only convey stormwater but also used to help to treat runoff, thus, reducing stormwater (runoff) pollutants. Like ditches, swales collect stormwater from roads, driveways, parking lots and other hard surfaces. But, unlike ditches, swales are not deep with straight sides. They have gently sloping sides and are substantially wider than they are deep. They are also vegetated to prevent the slopes from eroding and also to help filter pollutants during and after rainstorms.

What Are Swales?

Swales systems consist of two components; berms and swales. Berms are raised areas of land used to contain a flow of rainwater and/or stormwater. Swales are the lowered areas of land used to allow the stormwater to percolate into the ground. Berms may be of varying size from large projects spanning out over miles to small swale systems positioned in a single parcel of property. Many property owners may shy away from the idea of constructing a swale system due to the perception that it may create an “eye-sore”. This is untrue, as swale systems may be landscaped and the different levels of the swale system add a sense of depth to the yard. Swales systems may also provide flood protection, as well as environmental protection.

Why Are Swales Important?

Since 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. This reduces the water’s speed and 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 downstream.

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.

Don’t misuse your swale

  • Do not pile garbage, trash, leaves, limbs or garden debris in swales – this adds pollutants, which can wash into downstream waters.
  • Do not pave the swale. This will reduce the percolation of runoff.
  • Do not park vehicles in the swale. This compacts the soil so that less runoff soaks in. Not to mention the pollutants that are left by your vehicle.

Let the water pond

  • Runoff should temporarily pond in the swale fro 24 to 36 hours. (Mosquitoes will not be a problems unless the water ponds for a period of time exceeding 72 hours)
  • Don’t damage or remove swale blocks or check dams
  • Don’t increase driveway culvert sizes
  • Don’t lower the driveway culverts

Add swales to your yard

  • Waterfront property owners may benefit from building 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.

The Florida Yards and Neighborhoods program operated from the Pinellas County Cooperative Extension Service is a program that has proved to be an excellent source of information regarding stormwater management. You may choose to contact them at (727) 582-2100 or through email.

The Florida Yards and Neighborhoods program has a certification program called the Florida Friendly Yard Certification. If your yard measures up, you'll receive a Florida Friendly Yard Certificate and an attractive sign to nestle in your garden. Program representatives work with individuals and small groups of homeowners to recognize and address areas needing enhancement in their yards. Informative publications by researchers at the University of Florida are provided upon completion of the Homeowners Survey, which recognizes current landscape practices.

If you would like more information regarding swales and stormwater treatment, contact the Public Works Department at 727.363.9243.