Operation and maintenance (O&M) of swales
Overview of Typical O&M Issues
A grass or dry swale is a general term for filtration or infiltration conveyance practice, but there are a wide variety of designs depending on the site requirements. The key functions of swales are to convey water with reduced peak velocities and to perform water quality treatment with filtration and infiltration. Swales have the benefit of providing ecological function in areas dominated by development and impervious surface. These practices are ideal for urban settings, which creates an opportunity for humans to impact their function through vandalism, littering, and vehicular traffic.
These practices, like other green stormwater infrastructure, require regular maintenance to ensure proper and long-lasting ecosystem and stormwater function. If properly maintained, swales can operate effectively for 20-50 years, depending on the design type. Vegetated dry swales may perform properly for up to 50 years (Malvern Borough, 2013). The most frequently cited O&M concerns for swales include: *
- Standing water in the swale after a 48 hour timeline to infiltrate runoff.
- Loss of volume storage due to accumulated sediment.
- Clogged soil media.
- Clogged inlet and outlet structures, or underdrains.
- Growth and proliferation of weeds or other non-native species that threaten the long-term effectiveness of the swale.
The sections below describe best practices to prevent or minimize these common problems.