May 27, 2021 By Katie Roundtree

Streets and swales are an important part of Northern Palm Beach County Improvement District’s overall stormwater management system. The storm sewers located below the street, ditches or swales located along the street, and the roadway itself serve to convey stormwater to designed locations. It is important to understand the basics of how streets and swales are used to convey stormwater, in order to identify when problems may occur.

Streets

Did you know that in very heavy rains, some water standing in streets or swales is part of the flood control design plan and is expected? Many streets are designed and built with curbs and gutters along the street and storm sewers underneath the pavement. The curbs and gutters direct stormwater from the pavement into the storm sewers. These storm sewers not only collect water from the roadway, but also connect to other drainage systems to collect water from yards and subdivisions and transport the stormwater to lakes, canals and other outlets.

As water flows from the streets into the lakes, your neighborhood lake’s water level may seem to rise quickly during heavy rain, but that’s not likely to last. If the system in your neighborhood is working properly, levels will return to normal soon after the rain has stopped. A more widespread and longer-lasting rain event will require more time for local, secondary and regional systems to absorb the excess water.

At times, blockages can occur, which can cause undesired flooding conditions and roads to become impassable. Many stormwater blockages in streets occur due to clogged storm sewer inlets. If there is an inlet in the street adjacent to your home, residents are asked to keep this drain clear of all obstructions including leaves, grass and debris. Debris at storm sewer inlets also build-up after a storm event, which is a good time to check the inlet to make sure that the system will work well in the next storm.

Swales

Chances are if you’ve lived in South Florida long enough, you’ve heard at least one person use the word “swale.” A swale is a graded and engineered grassy area of land appearing as a linear, shallow, open channel, that stretches from the edge of the sidewalk in front of homes (or the property line if there is no sidewalk) to the edge of the street.  Swales are typically vegetated with flood tolerant, erosion resistant plants.  Swales are one of the most commonly used stormwater practices. For many years, swales have been used to direct runoff from rural highways and residential streets. Today, swales not only direct stormwater but also help filter runoff and reduce pollutants.

A swale slows down the rapid flow of stormwater runoff by ponding water between its sloping sides, often called berms. The ponding not only slows the rate of flow but allows pollutants to settle out of the water. Ponding facilitates water quality improvements through infiltration, filtration and sedimentary deposition. Collected stormwater is expected to drain away through the soil within several hours or days. When the swale becomes full, the cleaner surface water will spill over the berm and slowly run into a local water body. Eventually, the remaining ponded water will either evaporate or infiltrate into the soil.

Here are some ways to maintain proper swales:

• Let water pond. Runoff should temporarily pond in the swale for 24 to 36 hours, sometimes even up to 72 hours.
• Mow the swale but keep it at a good grass growth. Tall grass slows water movement.
• Remove and compost leaves and grass clippings from swales.
• Minimize the use of fertilizers, pesticides and herbicides within 50 feet of a 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 reduces the filtration and infiltration of runoff.
• Do not park vehicles in the swale— this compacts the soil so less runoff soaks in. It also destroys the vegetation in the swale that is needed to filter the pollutants out of the water.
• Do not alter the design of the swale. Any changes will require a permit as they may affect drainage.

As we approach the rainy season in South Florida, it is important to keep in mind that some standing water in streets and swales is normal during heavy rains.  Streets and swales are an integral part of the stormwater system. If during or after a rain event you arrive upon a roadway where you cannot determine the depth of the water in the street – for your own safety – do not drive down the street. Find an alternate route.  Cars can lose traction in as little as six inches of water.  If you are not sure of how deep the water is, turn around.