Vegetation establishment is an important component of many stormwater control measures (SCM). Grasses, trees, shrubs, and other herbaceous plants help provide structural stability, conrol erosion, and naturally remove pollutants from rainwater runoff. However, if proper maintenance is not performed, undesirable vegetation will invade vegetated areas of the SCMs. If these undesirables go untreated, they can inhibit the function of the stormwater control to convey, treat, and/or store water from storm events. Furthermore, some desirable plants can become undesirable if they establish in unwanted areas. For instance, turf grasses invading a planted/mulched area or trees establishing on the floor of a dry detention basin.
Desirable vegetation needs periodic maintenance to ensure that it remains healthy and established. Desired plant communities can be detrimentally compromised through climate changes, lack of proper maintenance, infrequent storm events, vehicular/equipment traffic, and vandalism. In these instances, supplemental and replacement planting may be needed for effected areas. This should occur during the appropriate planting season for the particular plant species being used and need additional care until they are established.
The plants listed in the following sections reflect communities in the Southeast.
Turf-type grasses provide soil stability, reduce flow velocity, and maintain the structural integrity of SCMs.
Provisions should be made to reestablish a uniform cover of turf grass on areas damaged by sediment accumulation, stormwater flow, and/or other disturbances. Failure to maintain could result in structural failure.
Many times herbaceous plants and native/ornamental grasses are used to help the stuructural integrity of the SCM as well as remove nutrients and other pollutants from stormwater runoff.
Hebaceous plant material should be allowed to die-back at the end of the season.
Native/ornamental grasses should be cut back every 2-3 years depending on the plant's growth during that period. Cut back should be delayed until the later winter months to allow the plants' ornamental quality to show. Evergreen native grass such as Juncus should not be cut back as they provide pollution uptake while other plants are dormant.
Trees and shrubs are often used with SCMs to provide shade and help control water temperatures. High water temperatures and direct sunlight can cause an increase in algal blooms. Trees surrounding SCMs also help provide a safety barrier for people and blend the SCM into the landscape.
Tree and Shrubs should be maintained in a healthy condition. They should be monitored forr disease or insect infestation problems and treated accordingly.
If maintenance is not performed properly, undesirable vegetation will dominate the vegetated areas of the SCM. These plants are aggressive in nature and have seeding habits that are unwanted where species diversity in desired.
Remove undesirable vegetation before it is established. Once established, these plants can have an adverse effect on the survivability of desirable plants and the aesthetic appeal of the SCM. The best time to do this is during routine maintenance activities. Undesirable plants can be removed by physical, mechanical, and/or herbicidal practices. Dispose of the trimmed plant material properly; do not discard into waterways because the material could clog the waterways and add nutrients to the water.
NCDOT SC Inspection and Maintenance Manual (NCDOT-HS-2010-01)