Green Infrastructure

Gravel wetlands are similar to a regular stormwater wetland except it is filled with crushed rock or gravel and designed so that the rock or gravel is submerged. Wetland plants are rooted in the media along with thriving algae and microbes on the rocks. This structure relies on the pollutant-stripping ability of plants and soils to remove pollutants from runoff.

Routine maintenance should be performed on gravel wetlands. 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 gravel wetlands, see [link to Appendix D: Planting and Soil Guidance].

In addition to routine maintenance, gravel wetlands 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 gravel wetland. If the gravel wetland is not draining properly, check for clogging in the inflow and outflow structures.

Over a period of time, if the forebay or gravel wetland has received a significant amount of sediment, then the sediment at the bottom of the forebay- or gravel wetland may need to be removed. Sediment excavated from wetlands that are not stormwater hotspots are not toxic and can be disposed through land application or landfilling.

The embankment of the gravel wetland should be inspected regularly for trees and animal activity. Trees growing on the top or sides of the embankment should be removed. Animals can burrow holes weakening the structure of the embankment.

Fertilizers should only be used sparingly during the establishment of the practice. After the practice is established, fertilizers and pesticides should not be used.

Here are some of the common problems to be aware of when maintaining a bioretention area. They include, but are not limited to, the following:

• Sediment build-up
• Clogging in the inlet and outlet structure
• Establishing vegetation within the wetland area
• Maintaining proper pH levels for plants
• Pruning and weeding to maintain appearance
• Mosquitoes breeding in the practice

Should the enhanced swale become a breeding ground for mosquitoes, the problem is likely with the soil media or the overflow structure.