About Vegetated Swales
General Information Performance Data Water Quality Treatment Process Design


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Design

Swales are easy to design and build. They can be rock-lined or vegetated, broad or narrow, curving or linear, natural or engineered. Vegetated swales are generally designed with a trapezoidal or parabolic shape to accommodate large fluctuations in the flow of stormwater runoff.

Dense vegetation is key to a swale’s stabilization and function, yet it is often not established until years after the construction is complete. This lag is common, and results from the fact that dense root mats may take up to three months to develop depending on the local growing season—a requirement that often is not accommodated by construction calendars.

Typically, state design criteria for all swales, including those that are vegetated, specifies slopes of less than one percent, and flow velocities of less than one foot per second for 10-year (Q10) and lower flows. In general, swales installed in steeply sloped areas do not meet the design requirements for slope and velocity. Other common sizing criteria, such as water quality volume (WQ_V), channel protection volume (CP_V), and conveyance protection volume (Q_p), were not used in the design of this system.