NEW APPROACHES TO “GREENING” STORMWATER

The past five years has seen a renewed interest in the use of stormwater best management practices (BMPs) that incorporate vegetation and/or are designed to mimic the functions provided by the natural vegetative cover. A variety of terms (e.g., green infrastructure, low impact development) are used to describe this wide range of BMPs, but the common denominator is that they all reduce the total annual runoff volume using rainfall interception, soil infiltration, evaporation, transpiration, engineered infiltration, and/or extended filtration. This paper explores some of the recent state and local approaches toward using these practices, collectively referred to here as green stormwater BMPs.The concept of using green stormwater BMPs to reduce and treat stormwater runoff is not a new one. The recent interest in these BMPs is perhaps a result of the realization that the conventional approach has not been successful in terms of improving the quality of our receiving waters and achieving pollutant reduction and ecological restoration goals. It may also be due to the realization that green stormwater BMPs provide so many secondary benefits, such as air quality improvement, regulation of air temperature, aesthetic appeal, and wildlife habitat.Even where interest in these BMPs is high, actual application of green stormwater BMPs has been somewhat limited by barriers such as conflicting local code and ordinance language, skepticism about new approaches by developers and local officials, and a lack of technical guidance or good data on performance. The latest approaches taken by communities to “green” stormwater begin to address some of these barriers and seek to promote better stormwater design and management. The following three strategies are summarized in this paper, and are supplemented with specific examples from around the country:Adopting new stormwater criteria that focus on runoff reductionDeveloping credit systems that provide incentives for using green stormwater BMPs, andImproving BMP designs to increase pollutant removal performanceSeveral east coast states are leading the charge to promote green stormwater BMPs for stormwater treatment using a runoff reduction approach. The states of Georgia, Virginia, and Delaware are all in the process of revising their stormwater regulations and/or design manuals and are highly interested in promoting the concept of natural systems for stormwater treatment. A brief overview of this approach and status of the work in each state is provided in this paper.A number of states and local governments have adopted stormwater credit systems as part of their stormwater management programs that encourage the use of green stormwater BMPs by reducing the size and cost of structural BMPs needed based on the runoff reduction or pollutant removal benefits provided by green stormwater BMPs. Although the details of each system vary, the most effective credit systems specify minimum criteria to be met to be eligible for the credit, and provide simple guidance on how to calculate the credit. These credit systems directly translate into cost savings to the developer by reducing the size of storm water storage and conveyance systems required. Some examples of innovative stormwater credit systems from around the country are described in this paper.The current menu of stormwater BMPs is not capable of reducing nutrients and other pollutants to urban land targets for pollutant loads in the Chesapeake Bay watershed and other regions of the country. There are several reasons why communities get such modest pollutant reduction from the stormwater BMPs they require at new development projects. For example, they often accept BMPs that have low or negligible removal rates on a significant proportion of their development sites, they do not encourage green stormwater BMPs because they lack detailed design criteria or defined pollutant removal rates, and the BMPs used often achieve lower performance than expected due to poor design, installation or maintenance of practices in the real world. Two recent initiatives to improve pollutant removal performance through enhanced BMP design are described in this paper.