Swales for Stormwater Management: How They Work & The Best Types for Your Project

Swales are some of the most practical stormwater infrastructure tools available for industrial and commercial sites. At a basic level, a swale is a shallow, sloped channel designed to move stormwater across a site more slowly and more deliberately than a conventional ditch or storm pipe. 

In effect, swales reduce flow velocity, improve water quality, support infiltration where appropriate, and create a more resilient overall drainage system. For sites managing large hardscaped areas and evolving regulatory expectations, that makes them a valuable part of the stormwater system. 

Why Swales Are Needed 

Industrial development changes how water moves naturally through landscapes. Roofs, roads, parking structures and storage lots increase impervious cover, which means more runoff, which is also often faster and dirtier runoff. Left unmanaged, this can contribute to erosion, overloading of downstream systems, and the transport of sediment, hydrocarbons, metals, and other contaminants. 

Swales address that problem at the surface by slowing flow and providing an opportunity for filtration and, in some cases, infiltration. They are often used as part of a broader system that balances water treatment. 

How Swales Work 

Swales work by combining shape, slope, surface roughness, and vegetation or engineered media to manage runoff. As stormwater enters the swale, the channel spreads and slows the flow, which allows suspended solids to settle and gives water more contact time with vegetation, soils, or treatment media. 

Depending on the design, swales may: 

• convey runoff safely across a site  

• filter sediment and pollutants  

• promote infiltration into underlying soils  

• reduce peak flow rates  

• provide pretreatment before water reaches another stormwater facility  

 
Like most stormwater features, swales work best when they are matched to site conditions rather than treated as a one-size-fits-all solution. 

Common Types of Swales 

Several swale types are commonly used in industrial and commercial stormwater design. They may be vegetated (bioswales) or unvegetated. 

Rock-Lined Swales 

Rock-lined swales use riprap or coarse aggregate to handle higher velocities and reduce erosion in areas where vegetation alone would not hold up. They are often used where grades are steeper. 

Turf-Reinforced Swales 

These swales combine vegetation with reinforcement mats or structural support systems to improve stability under higher flow conditions. They offer a middle ground between a fully vegetated channel and a harder engineered conveyance feature. 

Concrete Swales 

Concrete swales are engineered for conveyance where infiltration and filtration are not the primary objectives. They are commonly used in tighter industrial settings with limited space or access. 

Underdrained Swales 

Underdrained swales include a subsurface drain system beneath the treatment layer to manage water where native soils infiltrate poorly or groundwater conditions limit infiltration. 

Check Dam Swales 

These swales incorporate small grade-control structures within the channel to spread water out and improve settling time. They are especially useful along longer runs where unmanaged velocity would otherwise reduce treatment performance. 

Filter Media Swales 

Filter media swales are built with engineered treatment media designed to improve pollutant removal beyond what vegetation and native soils can achieve alone. These are often considered where runoff quality objectives are more stringent or where contributing drainage areas carry a higher sediment or pollutant load. 

Dry Swales 

Dry swales are designed to drain down between storm events. They typically include an engineered soil layer and underdrain system, making them useful where some treatment is needed, but long-term standing water is not desirable. 

Wet Swales 

Wet swales retain moisture for longer periods and may support wet-tolerant vegetation. They can be effective in the right setting, but they require careful design and are not suitable for every industrial site. 

Conclusion: An Innovative Fit for Industrial Sites 

Swales are popular because they are flexible, visible, and effective when properly designed. These installments can support site drainage while helping proponents meet performance expectations without overcomplicating the solution. Just as importantly, they can often be integrated into grading and landscape plans without disrupting operations. 

Build the Right Stormwater Strategy from the Start 

Swales can look like simple landscaping, but they are in fact working infrastructure, and their value depends on how well they are integrated into the broader stormwater plan. 

At Nichols Environmental + Engineering, we help clients evaluate stormwater management solutions in accordance with local regulations. If you are planning a new development, expanding an existing site, closing down a facility or upgrading stormwater controls, our team can help you develop a plan that meets your needs. Contact us today to get started!