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Bioretention facilities, which are also often referred to as rain gardens, use a mix of plants and engineered soils to capture and treat stormwater before it is discharged to a conveyance system or allowed to infiltrate into the ground. Most commonly constructed as shallow depressions, Bioretention facilities can often be found in parking lots, along roadsides, and near areas with a large number of impervious surfaces. Bioretention systems are typically not designed to provide stormwater detention for larger storms or store stormwater for more than a few days.

How do Bioretention Facilities work?

During weather events, stormwater flows into a Bioretention cell, where it’s slowed by vegetation and thick mulch. Captured water percolates through engineered soil layers while also being absorbed by vegetation. As water travels through different soil mediums, nitrogen, phosphorus, heavy metals, suspended solids, and other pollutants are filtered. Now treated, stormwater continues through additional filter layers until it infiltrates the ground or enters a conveyance system.

Heavy weather events, which routinely result in excess stormwater, can prove challenging for standard Bioretention facility design. Bioretention facilities are often constructed with overflows and underdrains connected to storm drainage systems to handle such events. These enhanced design elements aim to increase drainage rates and prevent flooding during large storms.

When a heavy weather event occurs, stormwater enters the Bioretention facility like a typical weather event. Water will infiltrate the Bioretention system and enter the underdrain and connected stormwater drainage system. Any excess stormwater ponds until it reaches the raised overflow drain. Overflow enters the raised drain and traverses the conveyance system to a stormwater chamber or drainage system.

Maintenance Schedule

It is necessary to perform routine maintenance throughout the year to make certain that the Bioretention cells are able to continue functioning correctly. The maintenance of mulch, plants, and soil helps to make certain of optimum filtration, pollution and storage capabilities. Most routine maintenance procedures are standard landscape care activities that are able to be carried out with common tools.

Sediment should be removed and curbs cleaned in early spring and late fall. Weeds should be removed and new plants watered during the summer months as well as early fall. New plants will need to be watered for the first three summers, while litter and debris should be removed throughout the year when required.

The maintenance tools required will be a rake, gloves, a bucket lined with trash bags, and if working close to traffic or motorists, safety equipment such as high visibility clothing and traffic cones.

Make sure you have correctly identified and removed weeds prior to them producing seeds. Three inches of mulch should be maintained to assist with the survival of plants.

Signs to look out for that indicate a need for maintenance include exposed, bare soil that does not have a lot of mulch cover, a large amount of waste from pets, water ponding for more than two days following a storm, dead or unhealthy vegetation, and pest infestations such as rodent holes or mounds that are disturbing water dispersion flow paths and damaging vegetation.

Stormwater Management

Stormwater management is a vital factor in all land development projects. Development disrupts the natural cycle of water. Rainfall that would once have infiltrated the undisturbed soil now runs along the surface. Land development also yields structures, pavement, and other surfaces that stormwater cannot penetrate. Stormwater management methods were developed by engineers, with Bioretention facilities being one of those methods to mitigate this problem.

Benefits of Bioretention Facilities:

Water Quality

Bioretention is a superb stormwater treatment practice because of the variety of mechanisms for the removal of pollution, including biological and microbiological uptake, settling, infiltration, soil absorption, vegetative filtering, evaporation, and transpiration.

Bioretention is able to be designed as an effective practice for infiltration and recharging, especially when parent soils have a high degree of permeability. Bioretention designed for infiltration makes use of engineered media that is excellent for the removal of soils and the majority of organic chemicals and metals.

Water Quantity

Bioretention can also be designed as a highly effective practice for infiltration and recharging with highly permeable parent soils. When soils have lower permeability an underdrain is usually used to achieve some infiltration and rate control.

Habitat Improvement

Bioretention facilities that have been correctly designed can provide a good habitat for invertebrates. These benefits are considerably improved when several different Bioretention practices exist in a landscape.

Community Livability

Aesthetically, Bioretention is a pleasing practice that is easy to integrate into a variety of landscapes and can also make use of a wide array of vegetation including trees, perennial plants, and trees.

Health Benefits

A number of studies indicate that green spaces can cause both physical and mental health improvements for residents and even result in a reduction in crime.

Economic Savings

Bioretention practices that have been correctly designed and integrated are able to offer cost savings over their entire life cycle. Bioretention practices that are well designed and maintained can also have a positive impact on property values.

At Muller, Inc., we use our extensive knowledge and specialized technologies to design and construct Bioretention facilities throughout Virginia, Maryland, and Washington, D.C. Contact us today via our website or by calling 703-560-4040 to learn more about Bioretention facilities and the complete list of green infrastructure services we offer.