Stormwater May 2012 : Page 19

empties into Hudson Bay. The soils in the basin are fertile, but mostly clay from sediments deposited during the last ice age. According to the US Geological Survey, there have been signiﬁ cant ﬂ oods here since the ﬁ rst anecdotal ac-counts in the mid-1700s. Some have been caused by heavy rain alone and by heavy rain on frozen ground, but the majority have been caused by the melting of above-average snow packs in the spring. Since the ﬂ ood of 1997, though, when the water rose to 39.57 feet, ﬂ ooding seems to be increasing in intensity as well as in frequency. “In 2009, they had a record event,” says Jim Schulz, senior engineer with the city of Moorhead. “It made the 1997 ﬂ ood seems like small potatoes.” The 2009 ﬂ ood, the new ﬂ ood of re-cord, rose 40.84 feet. The city used a combination of sandbagging and clay levees as temporary contingency mea-sures, Schulz says, but many of the storm sewers didn’t have gates and required temporary measures such as plugs and sandbags. These temporary measures worked, but they were time consuming and not as reliable as gated structures. The city has been working on a number of ﬂ ood protection projects since then, both permanent and tem-porary. “There’s generally a consensus with the city of Fargo on what needs to be done,” says Schulz. One measure Moorhead has taken is to develop an action plan based on the depth of the ﬂ ooding. For example, at 15 feet, city workers raise the bike bridges. By 17 feet, they begin to close roads. By 28 feet, they begin to close bridges, and by 35 feet, they begin to build temporary levees. The city is also using computer modeling to create interactive maps, a depth grid, and a graphic that depicts ﬂ ow conditions and the estimated ar-rival time of the ﬂ ood peak. For ex-ample, Schulz says, if the National Weather Service reports that a ﬂ ood is moving at 32,000 cubic feet per sec-ond, the model will show what it will look like. Moorhead is building protection to the ﬂ ood of 2009, 40.84 feet, plus 3 feet of freeboard, he says. The US Army Corps of Engineers estimates that a 100-year ﬂ ood would be close to 42.5 feet without a diversion around the city. With a diversion in place, it es-timates that a 100-year ﬂ ood would be 30.8 feet and a 500-year ﬂ ood, 40 feet. The temporary measures are ad-equate in conjunction with the per-manent ones, ﬁ rst because the main reason for ﬂ ooding in the spring is snowmelt, which ﬂ ows slowly, so to date there has been time to prepare; and second, because many perma-nent measures have been constructed since the 2009 ﬂ ood. These reduce the number of temporary measures re-quired and therefore the time required to construct them. Workers are lining a ditch with a concrete liner so ﬂ oodwater can move more efﬁ ciently through the city. Ad-ditional levees are also being built. The city is upgrading the storm and sanitary sewers and installing sanitary reliableliftstations.com LIFT STATIONS SO RELIABLE, YOUR SERVICE MANUAL WILL COLLECT DUST. WE GUARANTEE IT WITH THE BEST WARRANTY IN THE BUSINESS. From the durable NidaFusion STO enclosures, to our custom-engineered controls, to our unrivaled line of self-priming and submersible pumps, every component in a ReliaSource ® lift station is 100% manufactured, assembled, tested, and installed by the experts at Gorman-Rupp. That’s how we know our lift stations will outperform and outlast any other lift station in the industry. And, thanks to our industry-leading 60-month warranty, you’ll know it too. With ReliaSource, you get equipment, a warranty, and a company you can rely on. Guaranteed. For more information about ReliaSource lift stations and the Gorman-Rupp warranty, visit reliableliftstations.com. THE GORMAN-RUPP COMPANY, MANSFIELD DIVISION P.O. BOX 1217 | MANSFIELD, OHIO 44901-1217 | USA 419.755.1011 | GRSALES@GORMANRUPP.COM | GRPUMPS.COM ª$PQZSJHIU&#0d;5IF(PSNBO&#0e;3VQQ$PNQBOZ&#0d; (PSNBO&#0e;3VQQo.BOTmFME%JWJTJPOJTBO*40&#1a;&#1b;BOEBO*403FHJTUFSFE$PNQBOZ May 2012 www.stormh2o.com 19

Stormwater May 2012 : Page 19

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