Swale vs Ditch: What’s the Difference?
Stormwater runoff is a big problem in many parts of the country. In order to try and mitigate some of the damage, homeowners and municipalities are employing a variety of methods to divert and control the flow of rainwater.
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One such method is the use of swales and ditches. Swales and ditches are both designed to redirect water runoff, but they function in different ways.
Swales are essentially shallow trenches positioned at a low point in a landscape to catch and divert water.
They are typically lined with rocks or other materials to slow the flow of water and promote infiltration. Ditches, on the other hand, are deeper and typically narrower trenches that are built to capture larger volumes of water more quickly.
The main difference between swales and ditches is that swales are designed to infiltrate water into the ground, while ditches are intended to move water away from a site as quickly as possible without causing erosion.
What is a swale?
Swales are shallow, V or U-shaped channels that are used that are built on the lowest spot of an area where water naturally accumulates. They are used to detain, infiltrate and evaporate water.
Swales are typically planted with vegetation that can tolerate wet soils and has deep rooting systems.
This type of vegetation helps to stabilize the swale, slows the flow of water, and promotes infiltration.
Swales alone cannot provide enough treatment to achieve entire stormwater treatment/water quality goals.
However, they can serve as an important pretreatment function before the water enters a stormwater management system such as an infiltration basin, wet pond, or constructed wetland.
Swales are commonly used in residential areas, parking lots, commercial developments, and parks. They are built along the road edge to reduce the flow of runoff into storm sewers.
What kind of vegetation is used in a swale?
Swales can be planted with a variety of species, including turf, sedges, and tufted grasses.
Vegetation must span the entire width of the swale, be able to endure design flows, and be dense enough to prohibit favored flow pathways and scour of deposited sediments.
Turf swales are widely utilized in residential areas and small commercial sites.
While they are not as efficient as some of the other vegetation options, they are less expensive, easier to install and maintain and provide a more natural look.
Trees and shrubs can also be used in swales and provide many benefits such as shade, windbreaks, and reduced runoff. They should be selected for their ability to tolerate wet soils and deep rooting systems.
Densely planted swales can become an urban landscape feature that requires little maintenance and can endure huge flows.
However, supplemental irrigation may be required to maintain dense perennial vegetation, which is also important for weed management.
When building swales around roads, driveway crossings are a must to allow vehicles and pedestrians to safely cross the swale.
Driveway crossings can be ‘at-grade’ or ‘elevated depending on the topography and the traffic control requirements.
‘At-grade’ crossings follow the profile of the swale and are typically constructed with the same material used to build the swale. While ‘Elevated’ crossings are constructed above the swale and require a separate structure, such as a bridge or plank walk.
What is a ditch?
Ditches are deep and narrow channels that convey stormwater runoff. Ditches typically have steeper sides than swales and are built to convey large volumes of water quickly away from a site without creating erosion.
Since water infiltration is not the main function of ditches, they may be built with a variety of materials, including concrete, asphalt, or stone.
Ditches are commonly used in areas where there is a high volume of stormwater that moves quickly. They channel water from where it accumulates to a downstream outlet, such as a storm sewer or stream.
What are the differences between a swale and a ditch?
| Features | Swale | Ditch |
|---|---|---|
| Function | Infiltrates, detains and evaporates water | Moves water away quickly |
| Shape | Shallow, V or U-shaped | Deep, narrow |
| Material | Typically lined with rocks or other materials | Concrete, asphalt, or stone |
| Vegetation | Planted with vegetation that can tolerate wet soils and deep rooting systems | Typically not vegetated |
| Purpose | Reduces the flow of water into storm sewers | Conveys large volumes of water quickly away from a site |
| Maintenance | Requires regular maintenance but typically less than ditches | Requires regular maintenance |
| Installation and upkeep cost | Typically lower than ditches | Typically higher than swales |
| Ideal use | Residential areas, parking lots, commercial developments, and parks | Industrial or transportation corridors |
| Benefits | Encourages infiltration and protects water quality, can improve biodiversity and habitat | Typically only used to move water away from a site |
| Appearance | Can be a beautiful addition to any landscape | Typically not meant to be seen |
The main differences between a swale and a ditch are that swales are designed to infiltrate water into the ground, while ditches are designed to move water quickly away from a site.
Swales are also typically shallower than ditches and have vegetation that helps to stabilize the swale and promote infiltration. Ditches are often built with a harder material, such as concrete or asphalt, which does not allow for water infiltration.
Swales are typically used in residential and commercial areas, while ditches are more commonly used in industrial or transportation corridors.
Swales are also typically used to reduce the flow of water into storm sewers, while ditches are used to convey large volumes of water quickly away from a site.
Swales can also be used as a landscape feature, while ditches are typically not meant to be seen.
Both swales and ditches require regular maintenance, but swales typically need less maintenance than ditches. Swales must have a vegetative cover to be effective, while ditches can be built with a variety of materials.
Installation and maintenance costs are typically lower for swales than ditches. Swales also provide many benefits like encouraging infiltration and protecting water quality.
A well-planned and vegetated swale can be a beautiful addition to any landscape and can help improve biodiversity and habitat while reducing runoff.
Conclusion
Swales and ditches are both types of drainage structures that convey stormwater away from a site.
They have different purposes and are built with different materials. Swales are designed to infiltrate water into the ground, while ditches are designed to move water quickly away from a site.
Swales are typically shallower than ditches and have vegetation that helps to stabilize the swale and promote infiltration. Ditches are often built with a harder material, such as concrete or asphalt, which does not allow for water infiltration.
Finally, swales provide many benefits like encouraging infiltration and protecting water quality, while ditches are typically just used to move water away from a site.