Green Infrastructure

An enhanced swale is a vegetated open channel designed to capture and treat stormwater runoff within dry or wet cells formed by check dams or other means.

Dry Enhanced Swale

A dry swale is composed of a filter bed of prepared soil that overlays an underdrain system. They are designed to let stormwater be filtered or infiltrated through the bottom of the swale. Because they are dry most of the time, they are often the preferred option in residential settings.

Wet Enhanced Swale

Wet swales are designed to retain water or marshy conditions that support wetland vegetation. Because this practice is meant to retain water, they are generally used in areas with a high water table or in areas with poorly drained soils. Wet swales established with wetland plant species help with pollutant removal.

Routine maintenance should be performed on dry or wet enhanced swales. During the first year that the enhanced swale is built, maintenance may be required at a higher frequency to ensure proper establishment of vegetation in the practice. For more information on vegetation within a swale, see [link to Appendix D: Planting and Soil Guidance].

In addition to routine maintenance, enhanced swales require seasonal and intermittent maintenance. For example, in case of snow, ensure that snow does not impact infiltration capacity. During the winter, make sure the materials used to de-ice surrounding areas stay out of practice to avoid clogging and further pollution.

After a large rainstorm, keep drainage paths, both to and from the area, clean so that water can properly infiltrate into the ground. If the enhanced swale is not draining properly, check for clogging in the inlet and outlet structures.

Fertilizers and pesticides should only be used sparingly and if necessary.

Here are some of the common problems to be aware of when maintaining an Enhanced Swale. They include, but are not limited to, the following:

• Sediment build-up
• Clogging in the inlet and outlet structure
• Establishing vegetation
• Clogging the underdrain (if applicable)
• Mosquitoes breeding in the practice
• Ant mounds
• Maintaining the proper pH levels for plants
• Pruning and weeding to maintain appearance

Enhanced Swale Routine Maintenance Schedule
Schedule	Activity
As needed or 4 times during growing season	Prune and weed to maintain appearance. Dissipate flow when erosion is evident. Remove trash and debris. Remove sediment and debris from inlets and outlets. Remove sediment build-up within the bottom of the swale once it has accumulated to 25% of the original design volume. Remove and replace dead or damaged plants. Mow as necessary to maintain a grass height of 4-6 inches, ensuring grass clippings are not placed in the practice. Observe infiltration rates after rain events. Dry enhanced swales should have no standing water within 48 hours of a storm event (though 24 hours is more  desirable). Inspect for evidence of animal activity.
Annually (Semi-annually the first year)	Inspect for erosion, rills, or gullies and repair. Replant wetland species (for wet swale) if not sufficiently established. Test the planting soils for pH levels. Consult with a qualified licensed professional to determine and maintain the proper pH levels. Inspect pea gravel diaphragm for clogging
As needed or during winter months	Trim planting material. Inspect for snow accumulation.
2 to 3 years	Replace/repair inlets, outlets, scour protection or other structures as needed. Implement plant maintenance plan to trim and divide perennials to prevent overcrowding and stress. Check soil infiltration rates to ensure the dry enhanced swale soil is draining the water at a proper rate. Roto-till or cultivate the surface of the sand/soil bed of dry swales if the swale does not draw down within 48 hours