volume reductions through infiltration and transpiration during entire monitoring studies. Total volume reductions during a study were calculated based on comparison of the total inflow volume and outflow volumes measured over the duration of each study (including multiple up to 65 - storm events). As these analyses utilized long-term observed volume – reductions over a series of storm events, they provide a valid comparison to the capture efficiency and volume reduction criteria contained in this TGD that were developed upon hydrologic simulations and summaries. Table XIII.1: Volume Reduction Summary of Biotreatment BMP Categories in the International Stormwater BMP Database Source: International Stormwater Best Management Practices (BMP) Database, Technical Summary: Volume Reduction. January 2011. values provide a benchmark for comparing the performance of LID BMPs (infiltration, harvest and use, and evapotranspiration) against the performance of LID biotreatment BMPs, which under some circumstances, may provide a similar level of retention plus offer other pollutant treatment mechanisms. This analysis shows that while LID biotreatment BMPs are not designed to fully retain the DCV, they are capable of providing substantial volume reductions, on the order of half of the water that is captured and managed. This analysis further shows that a well designed LID biotreatment BMP that has been designed to capture 80 percent of average annual storm water runoff and has been designed to achieve maximum feasible volume reduction would be expected to achieve total long term volume reduction on the order of 40 percent of long term runoff volume. This means that a designer, faced with a LID retention BMP with a performance of 40 percent or less could substitute the LID retention BMP with a LID biotreatment BMP that is capable of carrying 100 percent of the DCV without impairing the overall performance of the site’s system of BMPs. This is because roughly 40 percent of the DCV will be incidentally infiltrated or evapotranspirated by the LID biotreatment BMP roughly equal or better than the low-performing LID retention BMP. Therefore, it is – appropriate to designate 40 percent retention as a threshold for eliminating the mandatory selection and use of a specific LID retention measure in favor of using LID bioretention BMPs that achieve a comparable or greater level of retention for the system as a whole. This threshold must not be used to reduce the site’s overall level of retention.
volume reductions through infiltration and transpiration during entire monitoring studies. Total volume reductions during a study were calculated based on comparison of the total inflow volume and outflow volumes measured over the duration of each study (including multiple – up to 65 - storm events). As these analyses utilized long-term observed volume reductions over a series of storm events, they provide a valid comparison to the capture efficiency and volume reduction criteria contained in this TGD that were developed upon hydrologic simulations and summaries. Table XIII.1: Volume Reduction Summary of Biotreatment BMP Categories in the International Stormwater BMP Database Source: International Stormwater Best Management Practices (BMP) Database, Technical Summary: Volume Reduction. January 2011. values provide a benchmark for comparing the performance of LID BMPs (infiltration, harvest and use, and evapotranspiration) against the performance of LID biotreatment BMPs, which under some circumstances, may provide a similar level of retention plus offer other pollutant treatment mechanisms. This analysis shows that while LID biotreatment BMPs are not designed to fully retain the DCV, they are capable of providing substantial volume reductions, on the order of half of the water that is captured and managed. This analysis further shows that a well designed LID biotreatment BMP that has been designed to capture 80 percent of average annual storm water runoff and has been designed to achieve maximum feasible volume reduction would be expected to achieve total long term volume reduction on the order of 40 percent of long term runoff volume. This means that a designer, faced with a LID retention BMP with a performance of 40 percent or less could substitute the LID retention BMP with a LID biotreatment BMP that is capable of carrying 100 percent of the DCV without impairing the overall performance of the site’s system of BMPs. This is because roughly 40 percent of the DCV will be incidentally infiltrated or evapotranspirated by the LID biotreatment BMP – roughly equal or better than the low-performing LID retention BMP. Therefore, it is appropriate to designate 40 percent retention as a threshold for eliminating the mandatory selection and use of a specific LID retention measure in favor of using LID bioretention BMPs that achieve a comparable or greater level of retention for the system as a whole. This threshold must not be used to reduce the site’s overall level of retention.
OC_TGD_Appendices_5-19-11.docx