Stormwater Facilities Maintenance

Underground utilities sometimes do not receive the attention that they deserve until they fail. This includes the facilities that collect and transfer stormwater from impervious surfaces to local streams and waterways. Stormwater management facilities must receive periodic maintenance to ensure their continued optimal service. Furthermore, these facilities occasionally need to be upgraded and improved to meet current environmental standards and accommodate advanced stormwater management practices such as water table infiltration, sediment and hydrocarbon removal and removal of other toxic substances, reduction of runoff velocity, and water temperature management.

Stormwater management facilities that are not properly maintained or upgraded can result in flooding, erosion, and damage to property. This tool is designed to address the critical needs of maintaining the operational effectiveness of existing stormwater management facilities and improving/upgrading those systems to meet current quantity and quality standards and other environmental requirements.

Advantages

The proper maintenance and retrofitting of stormwater management facilities can provide the following benefits:

Limitations

The following limitations can be associated with the maintenance and retrofitting of stormwater management facilities:

Implementation

Conventional Designs

Upgrading stormwater management facilities to improve their ability to control stormwater volumes has conventionally involved enlarging or deepening existing stormwater detention basins. Applicants should review the municipal stormwater ordinances prior to designing volume upgrades because many municipalities limit the depths of stormwater basins. Other conventional approaches to controlling volume involves slowing the rate of stormwater flow into the stormwater facility, by using a forebay (a small basin located near the inlet of a storm basin or other stormwater management facility designed to trap and settle out sediment and other pollutants before they reach the main basin) or the use of swales that lengthen the path from the collection site to the facility.

Stormwater Facilities Management

Stormwater facilities need to be periodically maintained.

Innovative Designs

A more proactive approach to stormwater quantity and quality issues addresses runoff closer to its source. This involves a variety of Best Management Practices that can be instituted closer to the headwaters of a particular watershed. These include stream restoration, wetland restoration and creation, improving ground cover such as reforestation, or reducing impervious coverage. Other measures include construction of infiltration structures and grading to promote sheet flow to promote natural infiltration.

Stormwater quality improvement measures can be retrofitted into existing stormwater facilities by using filtration or siltation structures that slow runoff to permit contaminants to settle out. Basins or structures that are specifically designed to remove sediment from the runoff must be maintained (i.e., the deposits must be periodically removed). Some designs have features that facilitate the easy removal of sediment and oils, such as structures that allow sediments to settle into a trap, and the use of oil/water separators.

Another method for improving the quality of stormwater runoff involves using plants to take up contaminants contained in the sediment load. Green roofs or vegetated roofs capture and temporarily store stormwater runoff in a growing media before it is conveyed into the stormwater drainage system. A portion of the captured stormwater evaporates or is taken up by plants, which helps reduce peak runoff volumes, runoff rates, and pollutants. These planting areas can also reduce the local "heat island" effect. Periodic removal of this vegetation eliminates the accumulated contaminants. Existing buildings with relatively flat roofs can sometimes be retrofitted with "green roofs".

Rain gardens and pervious paving can be retrofitted into existing stormwater management facilities. A rain garden is a planted shallow depression that captures stormwater runoff, while native plants take up the stormwater, or stormwater is filtered through soil layers before it reaches the groundwater level. A rain garden can also capture stormwater runoff that may contain pollutants such as hydrocarbons and excess nutrients that may otherwise contaminate waterways.

Pervious paving is sometimes used in conjunction with rain gardens, and involves the use of pavement materials that allow stormwater to pass through voids in the asphalt or concrete, and then infiltrate into the ground water table or into other stormwater management facilities. Porous pavements need to be cleaned (i.e., vacuumed) to remove fine materials that may obstruct the voids in the pavement.

Examples

Related References

Related Tools

Landscapes2 Relevance

Landscapes2, the 2009 Chester County Comprehensive Plan, promotes environmental protection. This tool is relevant to a number of Landscapes2 Water Resource Protection policies:

N.R. 3.2: Protect the recharge, quantity, and quality of ground water to sustain streams, wetlands and water supplies.

N.R.3.3: Protect, enhance and restore stream channels, base flows and water quality to sustain aquatic habitats and ensure a reliable water supply.

N.R. 3.9: Protect surface and ground water form contamination by all sources to sustain aquatic habitats, recreational uses and safe and reliable water supplies.

N.R. 3.10: Restore degraded and impaired streams and ground water to achieve state designated water quality standards and support upgrades in state stream designations where justified by stream conditions and uses.

N.R. 3.13: Encourage scientifically sound techniques and practices that reduce pollutants from point source and stormwater discharges, non-point source runoff, and on-lot and community land disposal systems.

N.R. 3.15: Support initiatives to improve water quality for the Delaware Estuary/Bay, Chesapeake Bay and Christina River Basin.