Apr 24 2008
New resource – or at least a new look
After four years, Green Roof Resource is getting a new look. I am currently updating the site for better readability and organization.
While on the topic of renewing resources, this week I came across the International Stormwater BMP Database. The resource provides data from over 300 BMP (best management practice) studies evaluating performance of these systems. While the database was initiated in 1996, I stumbled across it after reading an article in the May issue of Stormwater. “Can Stormwater BMPs reduce bacteria?” reports that bacteria counts in BMP outlets vary widely, but in general retention ponds and media filters have the potential to reduce bacteria. There is concern that vegetative swales and other similar BMPs may attract wildlife and domestic animals increasing the concentration of fecal coliform in stormwater runoff from these systems. The concentration often exceeds the standard for recreational primary contact in waterways.
It was exciting to see that green roof runoff was included in the evaluation. However, with data being obtained from only one site (Hamilton Ecoroof in Portland, Oregon), analysis of the data was limited.
It would be interesting to evaluated BMPs in combination. For example, if retention ponds are effective at reducing fecal coliform concentration, can bioswales or green roofs reduce the size of a downstream retention pond to enable use of the BMP in areas where land is limited? Or is the apparent reduction simply an artifact of where these systems are typically used? For example, are retention ponds able to reduce fecal coliform concentration in the effluent simply because there is less in the influent? Perhaps in areas where fecal coliform is a greater problem, more conventional methods are appropriate. While fecal coliform concentration is a health concern and is contribute to beach and water closings access after rain events, one must not forget about the volume of storm events. BMPs are effective at reducing total volume of runoff entering waterways, and one should also consider the total load of contaminants exiting these systems in addition to the concentration of contaminants.