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Bioretention is a up-land water quality and water quantity control practice the uses the chemical, biological and physical properties of plants, microbes and soils for removal of pollutants from storm water runoff. Some of the processes that may take place in a bioretention facility include: sedimentation, adsorption, filtration, volatilization, ion exchange, decomposition, phytoremediation, bioremediation, and storage capacity. This same principle of utilizing biological systems has been widely used in the retention and the transformation of pollutants and nutrients found in agricultural and wastewater treatment practices. Unlike various other practices that control only peak discharge, bioretention can be designed to mimic the pre-existing hydrologic conditions by treating the associated volumes of runoff. The bioretention technique has led to the creation of a new, holistic development philosophy known as Low Impact Development (LID). LID is an a method of integrating stormwater management into an overall site design. Consult the Low Impact Development Center website or the Prince George’s County Low Impact Development Manual for specifics on LID practices and techniques.
Bioretention was developed to have a broad
range of applications. For the most effective site integration and
treatment results, an early analysis of the overall site design should be made.
Early analysis allows the designer to place bioretention facilities integrated
throughout a proposed site design. However, depending upon the specific
case, bioretention can be substituted for other stormwater BMPs with minimal
site configuration changes. The use of bioretention not only has the potential for water quality and quantity control, but also improves aesthetics and adds the many values of landscape diversity to a development. Bringing landscape diversity into the built environment establishes a unique sense of place. Furthermore, using bioretention can reduce development costs by combining the design and construction costs of landscaping and stormwater management. By design, bioretention does not require intense maintenance efforts. Therefore, in residential applications, the transfer of the maintenance obligations to the individual homeowners is a viable alternative. The Kettering Urban Retrofit Study found that nearly 70% of the property owners would perform yard and garden maintenance activities that would help safeguard the environment. Proper maintenance will not only increase the expected life span of the facility, but will also improve aesthetics and property value. Bioretention employs a simplistic, site integrated, terrestrial-based design that provides opportunity for runoff infiltration, filtration, storage and for water uptake by vegetation. Bioretention facilities capture rainwater runoff to be filtered through a prepared soil medium. Once the soil pore space capacity of the medium is exceeded, stormwater begins to pool at the surface of the planting soil. When using the recommended engineered soil mix with underdrain, ponding will last for less then ˝ hour- longer if the system is dewatered by infiltration alone.
Another potential conceptual element of bioretention is the control of runoff close to the source. Unlike end-of-pipe BMPs, bioretention facilities are typically shallow depressions located in upland areas. Bioretention facilities can be distributed across a development site which can result in smaller, more manageable subwatersheds, and thus, will help in controlling runoff close to the source where it is generated. The above information was derived from the Prince George's County Bioretention Manual, Illustration credit: Prince George's County Bioretention Manual, Photo credits: T.E. Scott & Associates, Inc. |
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