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should control rate-based systems such as swales and small manufac-tured vaults and fi lters. In regions with accumulated snow-fall in excess of about 12 inches (33 centimeters), the volume of the spring melt will be greater than the volume of the design event based Figure 9. Outlet design on runoff depth. While the volume of the spring melt is for many areas greater than rain events of statistical interest, runoff occurs over several days rather than a few hours. It there-fore does not necessarily follow that the volume of volume-based systems should be increased in response to the greater volume of the spring melt. Rather, the sizing method should be based on the desired performance, recognizing the possibility of slower settling velocities in colder water as previously mentioned. Also, sediment in the spring melt is generally fi ner than that of rain events unless traction sand dominates. However, research indicates that clays fl occulate more quickly at very low tem-peratures, increasing settling velocities above that otherwise expected. It is likely that the size of a wet basin can be based on the statistics of rain-generat-ed runoff events occurring in the summer/fall period. Extended detention basins may be another matter. It is likely that these basins should be sized to fully treat the spring melt to ensure meeting the volume performance goal. Methods for estimating snowmelt volume, and consideration for rain-on-snow events, are available. Snow-melt algorithms for simulation models have been reviewed. Reviews of the characteristics of snowmelt, effects on treatment systems, and appropriate design criteria are available, as well as guidelines for snow storage areas. Reference Minton, G. R. 2011. Stormwater Treatment: Biological, Chemical, and Engineering Principles . RPA Press. Gary R. Minton, Ph.D., P.E., is a consultant on stormwater treatment and the author of the book Stormwater Treatment: Biological, Chemical, and Engineering Principles . Scan here to share this article or read later. Get the app at http://gettag.mobi PROJECT PROFILE: Stormwater Detention PROJECT NAME: PRODUCT USED: TOTAL WATER STORED: LOCATION: PROJECT DESCRIPTION: Gaithersburg High School Basin 1: 10'-7" DoubleTrap Basin 2: 8’-4” DoubleTrap Basin 1: 185,742 ft 3 Basin 2: 89,270 ft 3 Gaithersburg, MD ® ® StormTrap was chosen to manufacture stormwater detention systems for a new high school in Gaithersburg, MD. Stormwater management regulations required the need for two detention basins installed on the school grounds. StormTrap assisted the project’s consulting engineer, ADTEK, in designing a J\Z[VT&#xKLYN;YV\UKZVS\[PVU[OH[^V\SKÄ[^P[OPU[OLWYVQLJ[ZP[LWHYHTL[LYZ “We selected StormTrap as the stormwater quantitative design as it had a small footprint and could be quickly installed,” said Shawn Benjaminson, P.E., Principal at ADTEK Engineers. www.STORMTRAP.com 1-87-STORMTRAP 1-877-867-6872 Copyright © 2011 StormTrap. StormTrap, SingleTrap and DoubleTrap are registered trademarks of StormTrap. U.S. Patent Numbers: 6,991,402 B2; 7,160,058 B2; 7,344,335