Stormwater June 2012 : Page 33
“SWMMing” Through Stormwater Management Challenges Projects in watershed modeling, fl ow analysis, real-time control, inventory-keeping, and permit management BY DAVID ENGLE U rban stormwater ruins picnics and ballgames, raises floods, snarls traf-fic, threatens safety, wreaks destruction, costs cities millions in damage and disrup-tion—and those are among the rela-tively short-lived effects. Stormwater runoff is also the leading source of water-quality problems nationwide, carrying sediment and other pollut-ants to lakes, streams, coastal estuar-ies, and even drinking supplies; one fairly recent persuasive report on this came from the United States National Research Council in 2008. The resulting management challeng-es run the gamut from practical design tasks for sizing culverts and channels to fl ood prediction and permit compli-ance. There’s a battery of software spe-cialized for each task: modeling fl ows over hundreds of square miles (above and below ground), triggering fl ood warnings, tabulating numbers stream-ing from rain gauges, ensuring MS4 success, performing GPS mapping or GIS tagging of thousands of related sites and assets, providing real time-control of system resources, and back-ing up and documenting an agency’s water-related zoning decisions. Here’s an assortment of projects around North America that are now using these tools. Photos: City of Austin Model predictions in September 2010 Lamar at 12th Street, September 2010 Austin: Flash-Flood Alley “We do have a serious problem with fl ash fl ooding in urban areas,” says Su-san Janek of the Austin, TX, Watershed Protection Department. “And we will do anything we can do that will give a warning or a forecast to the public and our fi rst responders and give them additional time.” Starting nearly a decade ago, the city began looking for stormwater modeling software that could be used for fl ood predictions. “We did an evaluation of our system in 2007, by a consultant who came in and evaluated our par-ticular [team’s function], which is fl ood warning,” recalls Janek. “He had sever-al suggestions for us to use in terms of predictive mapping and modeling and many different ways to go down that path.” One was the US Army Corps of Engineer’s suite of products—“which is excellent,” she says, “for regulatory fl oodplain maps.” But the department ended up using a proprietary model called Vfl o, work-ing with the RainVieux radar rainfall application, from Vieux & Associates Inc. of Norman, OK. Janek’s offi ce began testing Vfl o against the Corps’ suite in real time. Vfl o’s handling of geospatial rainfall every 15 minutes, “ingested into a hy-drologic model,” she says, turned out to be “extremely stable” on the desktop computers. By comparison, the Corps’ suite of models, used in a predictive setting—which the models were not de-signed for, she concedes—“had issues with desktop computer stability.” Free trial downloads of Vfl o are available from the vendor, she notes. Buying a license cost the department around $4,500 at the time of purchase. Added to this, at $11,000 a month, are the cost of the vendor’s hosting of the models, the 15-minute processed radar rainfall for 4,483 pixels (each pixel be-ing one square kilometer), one-hour forecast rainfall, fl ood threat scores, and an audible notifi cation service. That’s a lot of money, she concedes. But 10,000 Austin homes occupy a 100-year fl ood plain, and another 500 structures will be threatened with fl ooding in every fi ve-year storm or worse. “So,” she says, “anything we can do to give adequate warning to pull people out of fl ooding, or preemptively put up barricades prior to road closing, can save lives.” To begin using the forecasting sys-June 2012 www.stormh2o.com 33
"SWMMing" Through Stormwater Management Challenges
David Engle
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