Enhanced swales: Maintenance

The following maintenance procedures and preventative measures should be incorporated into a maintenance plan:

Grassed Swale depicted recently mowed (Source: Natural Resources Conservation Service, 2002).

Maintenance requirements for enhanced grass swales is similar to vegetated filter strips and typically involve a low level of activity after vegetation becomes established. Grass channel maintenance procedures are already in place at many municipal public works and transportation departments. These procedures should be compared to the recommendations below to assure that the infiltration and water quality benefits of enhanced grass swales are preserved. Routine roadside ditch maintenance practices such as scraping and re-grading should be avoided at swale locations. Vehicles should not be parked or driven on grass swales. For routine mowing, the lightest possible mowing equipment should be used to prevent soil compaction. For swales located on private property, the property owner or manager is responsible for maintenance as outlined in a legally binding maintenance agreement. Roadside swales in residential areas generally receive routine maintenance from homeowners who should be advised regarding recommended maintenance activities.

• Inspect Vegetation Density: Inspect for vegetation density (at least 80% coverage), damage by foot or vehicular traffic, channelization, accumulation of debris, trash and sediment, and structural damage to pretreatment devices. This should be done after any major storm event (>25 mm), and quarterly for the first two years while vegetation establishes, and then every 6 months annually going forward. Replace dead vegetation, remove invasive growth, dethatch, remove thatching and aerate (PDEP, 2006).

• Mowing: Ensure grass is mowed and maintained to a height between 75 to 150 mm. Ensure that grass is nto mowed too short or that lawn chemicals are incorrectly applied and could Mowing grass too short and incorrectly jeopardize function of the BMP. (University of Minnesota-Duluth - LakeSuperiorStreams, 2009).

• Remove Trash and Debris: Remove trash and debris from pretreatment devices, the swale surface and inlet and outlets. This should be done at least twice annually, and more frequently if desired for increased aesthetic reasons.

• Sediment & Erosion Control: Remove accumulated sediment from pretreatment devices, inlets and outlets on an as-needed basis and at least annually. Repair eroded or sparsely vegetated areas. Remove accumulated sediment on the swale surface when dry and exceeds 25 mm depth (PDEP, 2006). If gullies are observed along the swale, regrading and revegetating may be required.

• Soil: Till soil at swales bottom if water does not drain out within 48 hours (swales should drain within 24 hours). Remove sediment build up when the swales volume is reduced by 25 percent.

• Cold Climate Considerations: In colder climates after spring freshet/snow melt, any collected sand/salt from winter time road maintenance must be removed. Further replacement of damaged vegetation should occur as soon as possible after the melt when damage can be adequately surveyed. Added organic matter (generally mulch) may be required especially if drainage to the swale in question is from a corresponding parking lot of roadway. Finally, Deicing agents (salts) can damage soil structure by reducing the soils' organic matter content, inspect and ensure excess loading is not occurring in the feature. (University of Minnesota-Duluth - LakeSuperiorStreams, 2009).
  

For more detailed guidance, refer to STEP's Low Impact Development Stormwater Management Practice Inspection and Maintenance Guide and Swales Inspection and Maintenance Fact Sheet, both of which can be accessed here

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

Vegetated, open channels designed to convey, treat and attenuate runoff. Design variations range from simple grass channels, which are designed primarily for conveyance to more complex treatment and volume reduction designs like enhanced grass swales, and dry swales or bioswales.

A long narrow trench or furrow dug in the ground, as for irrigation, drainage, or a boundary line.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

Land owned by private individuals or companies.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

Initial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms.

Best management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

Mineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm.

a top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales.

The total mass of a pollutant entering a waterbody over a defined time period.

The net amount of something (e.g. chemical, such as phosphorus), calculated as the product of concentration and volume in a given time. Some BMPs significantly reduce loading of pollutants to the environment by reducing volume more so than concentration.

Sustainable Technologies Evaluation Program

Low impact development is a stormwater management and land development strategy applied at the parcel and subdivision scale that emphasizes conservation and use of on-site natural features integrated with engineered, small scale hydrologic controls to more closely mimic pre-development hydrologic functions.

A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include Source, Conveyance and End-Of-Pipe Controls.