Volume4,Issue5 May2008 - Advanced Drainage Systems, Inc. · 2020. 2. 19. · deepwater-tightbasinthathasthe capacity to store runoff. While the rockhasavoid,orstoragecapaci-ty, of

Stormwater Control OnThe Streets At SouthGlenn

May 2008

S tormwa te r • S a nita ry S e we r

Volume 4, Issue 5

Should credit or blame be placedon the designer of the originalenclosed shopping mall, an

essential of every modern commu-nity in the 1970s? These massive,permanent structures of block andmortar with asphalt parking lots andconcrete sidewalks got their birth inthe early 1950s as Americans beganforsaking the inner city for suburbanliving. In 1956, Southdale Mall openedin Edina, Minnesota, becoming thefirst enclosed, climate-controlled,two-story regional shopping mallin America. Southdaleʼs architect,Victor Gruen, is generally recognizedas the visionary who not justbrought retail outlets together, butin fact created an entire new con-cept of marketing. For Gruen, thatwas little compliment, since his truevision was a sense of community –with residences, schools, officesand hospitals – that was far fromrealized. Yet the public quickly madeSouthdale a commercial success,and developers followed the “buildit and they will come” trend so faith-fully that more than 40,000 similarcomplexes were built across thenation over the next 30 years.

“Big box” retailing and onlineshopping speeded the decline inpopularity of the venerable malls inthe 1990s, making them a primaryfocus of some kind of redevelop-ment. In many cases, the solutionhas been complete demolition of allor almost all existing structures andpavement followed by new devel-opment of mixed-use communities,not surprisingly much as Gruen hadimagined. With acres of imperviouspavement and minimal concern forrunoff, the old malls greatly con-

tributed to localized street flooding.Redevelopment requires that storm-water management be incorporatedthroughout the site, something thatin most cases was never in placebefore or was absurdly inefficient bytodayʼs standards.

Currently under redevelopmentin Colorado is the old SouthglennMall, which opened in 1974 on 77acres at University Blvd. and Arap-ahoe Rd. in unincorporated Arap-

ahoe County. In the 1990s, growthin nearby areas began drawing po-tential retail sales and tax revenueaway from the mall. Overall, the areawasnʼt conveying a strong identityor an image of quality, so whenChicago-based Walton Street Cap-ital purchased the property in 1999,it immediately began exploring re-development options. When City ofCentennial was formed in 2001, theSouthglenn property was included

C O V E R S T O R Y

Under The PavementStreets At SouthGlenn Development Puts

Stormwater Management Under Asphalt Parking Lots

The Streets At SouthGlenn is a mixed-use redevelopment of the former SouthglennMall by Greenwood Village-based Alberta Development Partners LLC.

Colorado Public Works Journal May 2008 Used with Permission

November 2005, City Council re-zoned the property, created Centen-nial Urban Redevelopment Authorityand proposed formation of South-glenn Metropolitan District afterapproving a detailed service planthat defined the services the District

in the incorporation. The property wassold to Greenwood Village-basedAlberta Development Partners LLCin 2005, and discussions with theCity regarding zoning and develop-ment requirements for a high-end,mixed-use project got serious. In

would provide and the powers itwould have. It would take the prop-erty owners to vote SouthglennMetropolitan District into existence,which they did. The service planallows the District to raise up to$85 million for public infrastructureimprovements through the sale ofbonds.

“Metropolitan districts are acommon tool in Colorado for financ-ing the public infrastructure portionsof large development projects,” ex-plains Tareq Wafaie, a planner withURS Corporation, which has pro-vided planning services to City ofCentennial since its incorporation.“Metro districts have the power toimpose an additional property taxmill levy within their district, and tosell general obligation bondssecured by the property tax tofinance improvements for trans-portation, flood control, utilities andother needs deemed for the goodof the general public.”

Alberta Development Partnerswas ready to create a modern andlasting mix of retail and residentialdevelopment that would be a re-gional shopping destination to manyand home to others. The companyhas a long list of successful similarprojects, including Southlands in

StormTech chambers are placed six inches apart on 2 1/2 feet of 1 1/2-in. rock spread on a nonpermeable rubber liner.Rock is placed and rough graded by wheel loaders and skid steers. Isolator row can be seen wrapped in fabric and withthe chamber end cap installed.

Fiore & Sons nears completion of excavation of Basin 1. Arapahoe Utilities &Infrastructure has already begun installing the rubber membrane liner and plac-ing rock and StormTech chambers, background.

the Denver metro area. Each desti-nation is varied and vibrant withupscale retail and restaurants inter-twined with complementing resi-dences all within an outdoor envi-ronment of parks and promenades.

Construction is well underwayon around 1.1 million sq.-ft. of retailspace and 125,000 sq.-ft. of officespace, along with 200 for-rent resi-dential units. The Streets at South-Glenn will be home to the Commons,a block-long park which will featurea grand fountain and fireplace,mature landscaping, lush gardensand a playground. It will be accentedby a splendid outdoor café, dedicat-ed pedestrian plazas and prome-nades featuring European fountains.

“The Streets at SouthGlenn willenergize the area by providing dis-tinctive shopping, dining, working,and living experiences,” says DonProvost, principal of Alberta Devel-opment Partners. “Weʼve broughttogether leaders in architectureand design to create a regional,mixed-use shopping destination withlocal culture and universal appeal.”

Stormwater management onthe site incorporates the latest insubsurface technology to collect,treat and slowly release runoff. Todesign the developmentʼs storm-water system, along with its waterdistribution and sanitary sewer sys-tems, Alberta Development Partnersbrought in CLC Associates Inc., aGreenwood Village-based companythat partnered with the developeron both the Southlands and North-lands development projects over thepast few years.

“With locations and elevationsof the new structures set,” explainsCLC Project Engineer TiffanyWatson, P.E., “we began theprocess of determining drainagepatterns on the site. We were ableto create low elevation points underparking areas where stormwatercollection basins could be installed.Once the basin locations wereidentified, we designed the collec-tion systems to feed each basin,working with Xcel Energy, QwestCommunications, Comcast andothers to avoid conflicts. Each col-lection basin needed to be able tohandle a 10-year storm event.”

Six collection basins of varyingcapacity were designed for thedevelopment. Excavation was per-formed and rubber membrane liners

were installed at each basin site atvarying depths below final pavementelevation. Rock sized between 3/4-and 1 1/2-in.-diameter was placed onthe liner at a depth of 12 inchesand molded polypropylene cham-bers were placed side-by-side, sixinches apart, as part of StormTechLLCʼs subsurface stormwater man-agement system. With the cham-bers installed, wheel loaders andskid steers placed more rock onthe chambers, filling between themand covering them with another 12inches. Permeable geotextile wasplaced over the rock to allow waterbut not sediment into the basinbefore soil was backfilled andbrought to grade and density forasphalt paving. What is createdbelow the parking lot is a 4 1/2-ft.-

Kael Blair, project supervisor for Arapahoe Utilities & Infrastructure, center, poseswith Jim Heintz, left, and Mark Kaelberer of Advanced Drainage Systems besideone of ten ADS water quality units being installed on The Streets At SouthGlenn.

AUI crews set manhole at The Streets At SouthGlenn. Atright, SEMSWA Inspector Amber Law checks sediment build-up at one of the siteʼs temporary detention ponds for erosioncontrol during construction.

deep water-tight basin that has thecapacity to store runoff. While therock has a void, or storage capaci-ty, of 40 percent, the 2 1/2-ft.-tallchambers have a 100 percent void.Together, each basin can absorbthe 10-year storm event and releaseit downstream at a controlled flowrate.

“The StormTech system is de-

signed to accommodate a widerange of site restraints and installquickly, streamlining basin con-struction,” explains Mark Kaelberer,Colorado-based sales representa-tive for Advanced Drainage Sys-tems Inc., supplier of the subsur-face stormwater management sys-tem. “The injection-molded cham-bers are light yet strong with a cor-

rugated arch design that isproven for structural integrity.The system is ideal for low-rise,wide-span installations such asbeneath parking areas, keepingexcavation and backfill costs to

a minimum.”ADS, the worldʼs largest pro-

ducer of HDPE corrugated plasticpipe, serves the stormwater drainageindustry through a global networkof over 42 manufacturing plants andover 30 distribution centers. In addi-tion to pipe, the company manufac-tures 16 standard HDPE WaterQuality Units and provides a com-plete line of fittings and other acces-sories, including StormTech® prod-ucts, Nyloplast® drainage structuresand a variety of geotextiles. At South-Glenn, a combination of productswere incorporated to complete thedevelopmentʼs stormwater manage-ment system.

“Runoff is collected at variouspoints and channeled to one of thesix basins,” Kaelberer continues.“Before it enters the basin, it passesthrough an ADS water quality unitto separate out sediment and oilsnormally associated with the ʻfirstflush.ʼ The water quality units alsoincorporate the use of a bypasssystem, which prevents resuspen-sion of captured solids.”

After flow passes through thewater quality unit, it enters Storm-Techʼs patented design for enhanc-ing the removal of total suspendedsolids. Known as the Isolator™ Row,the first row of StormTech cham-bers is surrounded with filter fabric.Water rises in the Isolator Row andpasses through the fabric throughperforations in the chamber side-walls as well as through its openbottom. Solids that make it throughthe water quality unit are capturedinside the Isolator Row, protectingthe adjacent storage chambers androck from loss of capacity due tosediment accumulation.

“The Isolator Row is designedto reduce the cost of maintenanceby capturing suspended sedimentin just one row of the basin,” saysKaelberer. “Maintenance is accom-plished through high-pressure jet-ting of the row, forcing sediment intothe adjacent upstream manhole orbasin where it can be vacuumed out.”

“The old mall had almost 1.2ADS water quality unit is in place adjacent tomanhole while AUI crews continue placing RCP.

million square-feet of parking andonly four storm sewer inlets,” Watsonadds. “Flooding on University andArapahoe was pretty common.”

So common in fact that City ofCentennial, along with CDOT, willbe completely reconstructing thestorm sewer infrastructure as partof safety improvements at the inter-section of University Blvd. (SH 177)and Arapahoe Rd. (CR 42). Raisedmedians will improve pedestriansafety as well as vehicle move-ments into and out of The StreetsAt SouthGlenn, and while the workis being done, new storm sewer willbe installed from Vine St. on thewest through the intersection to anew outfall that will discharge intotwo new detention ponds beforereaching Big Dry Creek.

“Roadway drainage at the inter-

section will flow through a new pipe,”explains Kurt Kellogg, P.E., withFelsburg Holt & Ullevig, City ofCentennialʼs consulting engineerson the transportation improvementproject. “Most of the drainage fromThe Streets At SouthGlenn devel-opment will tie into the new trunk-line and outfall into the new pondsin the Big Dry Creek drainage. Thewestern part of the developmentdrains west to SlaughterhouseGulch, and the City is alreadyunderway installing upgrades tothose storm sewers. The TIP con-struction will begin this summer.”

The intersection safety im-provements have been on the booksfor several years, but never gainedfunding. City of Centennial took thelead, accelerating the project dueto the private development occur-

ring. With CDOTʼs participation andoversight, Centennial officials planto have their projectʼs conclusioncoincide with the developmentʼscompletion in summer 2009.

“The Streets At SouthGlenn isan important project for the City,”explains Mike Connor, AssistantCity Manager for Centennial. “Citi-zens are anxious to again have someof the best shopping options in theregion nearby, but it will also bemuch more. The entire area will berejuvenated and citizens and busi-nesses nearby will hopefully seetheir property values rise. Just asimportantly, the City of Centennialwill demonstrate that it is a progres-sive city that is steadfast in its com-mitment to responsible economicdevelopment.” �

Infrastructure development team for The Streets At SouthGlenn includes, from left, Bob Christensen, URS Corp., Brett Sollee,Tiffany Watson and Kurt Mahnken, CLC Associates, Tareq Wafaie, URS and Jon Heimbach, Alberta Development Partners.

Shopping malls – most, if not all– were specifically constructed

so that shoppers could avoid thecongestion and hassle of “down-town,” with ample, to say the least,parking. As societyʼs lifestyles andshopping habits have changed overthe last decade, many malls haveexperienced a decline in customertraffic that has resulted in a loss oftenants. The typically large parcelsof land become viewed as under-utilized property, and sooner or laterare evaluated for redevelopment.When these sites are surroundedby existing development, they areknown as “infill” sites, and it is oftenthe surrounding development thatplaces the strictest limitations on thesiteʼs metamorphosis.

“Infill sites present great redevel-opment opportunities but usuallyhave unique challenges,” says KurtMahnken, P.E., former senior vicepresident and director of engineering

and one of the founding principalsof CLC Associates. “Stormwatermanagement can be particularlychallenging, as it has been on TheStreets At SouthGlenn.”

CLC Associates, based in Green-wood Village and with regionaloffices in Phoenix, Salt Lake Cityand Spokane, has been in chargeof developing the master plan for

the mixed-use redevelopment ofthe former Southglenn Mall for thepropertyʼs owners, primarily AlbertaDevelopment Partners LLC. Thetwo firms have partnered on otherrecent projects in the Denver area,including Southlands and North-lands. While those projects were/are new construction at the leadingedge of development, The StreetsAt SouthGlenn is, by definition, aninfill site, and CLC was challengedto make the new infrastructure workwith the existing infrastructure of thesurrounding development.

“The Streets At SouthGlenntypifies the complexities of infilldevelopment,” Mahnken explains.“Such a large site really needs tobe entirely developed at the sametime in order to make infrastructureimprovements affordable as wellas effective. Stormwater runoff isFederally-mandated for quality, andquality is commonly achieved through

Infill Developments Pose Greatest Challenges For Runoff Management

CLC Associates created the Master Development Plan for The Streets At SouthGlenn for owners Alberta DevelopmentPartners LLC. Both firms are based in Greenwood Village.

StormTech chambers are installed withrock and a rubber liner to create shallowbasins that can store runoff. The rockhas a 45 percent void, the chambershave a 100 percent void.

onsite detention and slow release,but land available for runoff deten-tion is hard to come by. Making suchaccommodations almost alwaysrequires some kind of trade-off.”

Conceivably, trade-offs can affectthe economics of a project to thepoint that the potential return oninvestment is not worth the risk.CLCʼs responsibility was to devisea solution that would be acceptableto all stakeholders. Because the sitehad minimal stormwater collectionand conveyance to begin with, re-development would require design-ing and installing a complete sys-tem of stormwater managementinfrastructure.

“The west half of the propertyhas always drained to the west andthe east half to the east,” Mahnkencontinues, “and we couldnʼt changehistoric runoff patterns. But runofffrom the old shopping center trav-eled overland – there was no realconnection to the surrounding stormsewers. So understandably, theexisting storm sewers were notlarge enough to handle the maxi-

mum peak flow that the redevelop-ment would create because theywere not designed to do so in thefirst place.”

Moreover, there is little changein elevation from the redevelopmentto the surrounding stormwater infra-structure. This meant that the depthof detention ponds constructed waslimited to maintain gravitational flowoff the site, necessitating greatersurface area for detention capacityand even less gross leasable areafor the developer.

Mahnken and the CLC designteam investigated subsurface deten-

tion systems, hoping to keep thebasins shallow yet provide enoughstorage capacity by increasingsquare footage. They found whatthey were looking for from Storm-Tech LLC, a Connecticut-basedmanufacturer that produces a systemutilizing polypropylene chambersthat is ideal for installation underparking lots.

“We tried to design a customary,conventional, onsite, abovegroundsystem of detention,” says Mahnken,“but the site would not have pen-ciled. We looked at RCP, but thelarge diameter needed would have

Isolator rows can be seen in these pictures of two different basins. Low flows, including the first flush, are forced into theIsolator Row, which traps sediment as flows to the basin pass through its fabric. Black HDPE pipe seen at left connects tochamber end cap to allow heaviest flows to bypass the Isolator Row and relieve inlet backup. Corrugated metal is set toblock the rock so that a light pole and its base can be installed after the parking lot is paved, background at right.

Chamber installation is a quick and easyone-at-a-time process.

cu.-ft., or 1.54 million gallons, ofstorage. A total of 2739 chamberswill be used along with 134,000sq.-ft. of impermeable liner and260,000 sq.-ft. of non-woven, filter-ing polypropylene geotextile. AUI isalso installing 16,000 feet of 4-in.-diameter PVC and RCP up to 42inches in diameter, with 80 man-holes and 75 inlets.

“The StormTech system hasbeen simple to install,” Rabold adds.“The chambers are really strongand did not deflect at all under theweight of the rock and heavyequipment.”

“The Cityʼs willingness to part-ner with the developer is what hasmade The Streets At SouthGlennpossible,” summed up Mahnken,a C.U. graduate with a water re-sources and land developmentbackground who recently retiredfrom the day-to-day operations atCLC but plans to remain closelyinvolved in selected projects. “Theywere willing and open to meetingweekly to work out technical issues.We have designed the stormwatermanagement system on empiricaldata, so it will be interesting to reallyevaluate the overall efficiency of thesystem, which we have completefaith in. The project should serve asa great example for future storm-water management projects.” �

made detention lower than the dis-charge point. We were immediatelyattracted to StormTechʼs system dueto itʼs shallow nature and ease ofinstallation.”

Designing the basins to handlethe required volume for a 100-yearstorm event was quickly deter-mined to be a deal breaker, so CLCre-evaluated the realities and pro-posed a system to City of Centen-nial that would efficiently control andtreat 10-year events.

“By managing 10-year events,”Mahnken says, “the system wouldprovide benefit for over 95 percentof all storms. With the 10-year sys-tem in place, and with less impervi-ousness of the new development,runoff volumes from a 100-year stormwill certainly be no worse than his-torically after redevelopment.”

The City agreed and acceptedthe design, as did Alberta. Arap-ahoe Utilities & Infrastructure Inc. is

installing the stormwater systemalong with water and sanitary sewerutilities. Excavating contractor Fiore& Sons Inc. is performing sitework,including excavation of the six ap-proximately 4 1/2-ft.-deep detentionbasins.

“The biggest challenge has beenkeeping the existing stores open,”explains AUI Project ManagerKevin Rabold. “We had to do quitea few temporary relocates to keepthe utilities in service. Itʼs certainlynot like working in an open field.”

ADS provided everything forconstruction of the detention basinsexcept the liner and rock, includingthe system chambers and end caps,water quality units, geotextiles andNyloplast ductile iron grates andPVC basins. Colorado Lining Inc.provided the liner and Lafarge pro-vided 6400-cu.-yds., or 16,000 tons,of rock for the different-sized basins,which combined will provide 240,633-

Non-woven filtering geotextile is placed over the rock-covered chambers, allowing water into the basin but not sediment.Nyloplast drain basin, right, will be capped with a ductile iron grate to create an inlet.

Reinforced concrete pipe and manholes await installation at The Streets At South-Glenn. Firebaugh Precast supplied the manholes and Rinker Materials suppliedthe RCP.

Similarities are right there amongthe many differences. Establish-

ing community is the first objectiveof all modern mixed-use develop-ments by Greenwood Village-basedAlberta Development Partners LLC.How itʼs achieved is never the same.

“We tell people weʼre not justbuilding a ʻTown Center,ʼ” explainsBryan McFarland, Albertaʼs principalin charge of development, “weʼrebuilding the center of town.”

The first of Albertaʼs modern “life-style center” developments com-pleted in the Denver metro area,Southlands at E-470 and Smoky HillRoad in Aurora, was constructed infour phases between October 2003and October 2006. Three morevery similar yet very different large,mixed-use/retail developments –The Streets At SouthGlenn,Northlands and Cornerstar – are setfor completion over the next fewyears, clearly showing AlbertaDevelopment Partners to be verybullish on its home state.

What the developments havein common is a return to traditionalvalues by restoring a sense ofplace for shopping and entertain-ment. Gone are the enclosed mallsand their massiveness: massivesize, massive imperviousness andmassive opera-tional and mainte-nance costs. By in-cluding office andresidential spaceamong a full spec-trum of retail, asense of commu-nity is fostered.Albertaʼs develop-ments are plan-ned to create acore where thereʼsnever before beenone.

“Southlandsfeatures a modernmain street witha classic movietheatre, premier

retailers and restaurants and uniqueboutiques,” says McFarland. “TheTown Square at the north end ofMain Street offers a large pop jetfountain, farmerʼs market and sea-sonal entertainment, making it agreat, casual place to spend time.”

A mix of architectural designgives each structure its own identity,helping to draw customers inside,something that was limited to onlystorefronts in the old malls. Together,the different design elements createa unique overall environment. Whilethe developer can execute the de-sign, itʼs up to residents in the areato create community by adoptingthe development as their own.

“We help to ʻactivateʼ our devel-opments to bring people togetherthere,” McFarland continues. “AtSouthlands, we subsidize events like4th of July fireworks and Christmastree lighting, and provide a venuefor events linked with nearbyCherokee Trail High School. Thisdoes much more than create one-time traffic for businesses; it helpsmakes Southlands the place to be.”

Where each development dif-fers starts with what has to be donejust to “pad the site.” Relocatingutilities, improving vehicle move-ments and pedestrian safety and

controlling stormwater are develop-ment costs that can make or breaka project.

On the 300 acres at Southlands,Alberta had to excavate about 4million cubic-yards of dirt to deliverthe pad and create primary deten-tion. At 158-acre Cornerstar, modi-fying the Cherry Creek floodplain wasnecessary. For 132-acre Northlands,improvements to Preble Creekinvolved constructing a 10-ft. by10-ft. conveyance structure thatbisects the entire site to allow thehistoric storm flow to pass throughthe site.

The Streets At SouthGlenn isAlbertaʼs first foray into under-ground stormwater management.How to handle drainage issues onthe 77-acre infill site was identifiedearly on as a big challenge, withparameters making going under-ground the only real economically-viable solution.

“The Streets At SouthGlenn sitson the crest of two basins,” explainsMcFarland. “We could not allow anycross-basin drainage, so creatingindividual detention structures withdiscrete outflows was an ideal solu-tion. Our project team linked cre-ative thinking with engineering prin-ciples to design not only the most

c o s t - e f f e c t i v esolution, but in factthe only solution.It required workingwith the City ofCentennial and theSoutheast MetroS t o r m w a t e rAuthority to makeit a reality, and wecertainly appreciatetheir cooperationand vision.” �

Albertaʼs Investment In Colorado Quickly Approaching $1 Billion

Southlandsʼ MainStreet offers morethan 150 retailers,restaurants andsecond floor officesuites.

Coloradoʼs youngest big city,Centennial, has the distinction of

being the largest city incorporatedin U.S. history. Residents took thematter into their own hands as sec-tions of unincorporated ArapahoeCounty were being seriously eye-balled for annexation in the late1990s. The quest for their own citytook almost two and a half years,but residents came together andvoted to incorporate City of Centen-nial in September 2000. Everythingbecame official on February 7, 2001,after Centennialʼs first public officialswere elected. Now, beginning itsseventh year, the statutory city istaking major steps toward estab-lishing its home-rule charter.

“Centennial is whatʼs known asa Mayor/Council-style statutorycity,” explains Assistant City Man-ager Mike Connor. “This classifica-tion is the first step in becoming ahome-rule city. Weʼve establisheda solid foundation of governmentwhile learning whatʼs important toour citizens when it comes to pro-viding services for the public good.City officials have worked to struc-ture operations that will responddirectly to demands, and that is re-flected in the draft City Charter thatwill be voted on by citizens laterthis year.”

There have been a lot ofchanges over the last year andplenty of new faces. Connor him-self is looking forward to celebrat-ing one year with the City nextmonth. What has worked for Cen-tennial as it has matured is con-tracting with others to provide serv-ices, with 100 percent cost recoveryfrom use taxes and fees on thoseservices. The City now is well on itsway to assuming many of those re-sponsibilities with its own employees.

Naturally, order and revenue areimportant to a city in its infancy, soit was critical to develop planningoperations, set development feesand establish procedures for per-mitting immediately. URS Corpor-ation was hired to provide land useservices and has done so from theCityʼs very first days. URS helped

set a schedule of development andland use fees, understanding thatthose fees needed to facilitate eco-nomic development and not deter it.Specific fees collected would pay forcorresponding contracted services.

“URS has done a great job pro-viding planning and urban designservices, engineering design reviewand construction inspection,” Connorsays. “Their resources are huge. Anew cityʼs, of course, are not. Thereis almost a trend toward privatiza-tion of municipal engineering serv-ices, but Centennial has always feltan obligation to bring planning andland use services in-house, and wehave assumed those responsibili-ties beginning this year.”

When The StreetsAt SouthGlennwas proposed in 2003, studies be-gan to determine necessary infra-structure improvements in thelocalized area, spurred by the de-velopment but necessary also to im-prove existing inefficiencies, suchas pedestrian safety and trafficmanagement. Utilities were also aprimary concern, and for the City,that meant stormwater manage-ment. Southglenn Mall was a posterchild for storm runoff causing streetflooding and that, coupled with morestringent stormwater quality dis-charge regulations, was seen as an

StormTech chambers are quickly and easily handled and installedwithout any extensive training or special equipment.

Streets At SouthGlenn Project Marks Centennial̓ s Coming Of Age

ADS water quality unit is installed inone of the developmentʼs subsurfacedetention basins.

important engineering challenge.“The developer is required to

control runoff to its historic levels,”Connor explains. “But the City hasto be able to accommodate thoseflows once off the site, which histor-ically has drained to both Slaughter-house Gulch on the west and Big DryCreek on the east.”

“Since there was virtually nostormwater management on the olddevelopment,” says Bob Christen-sen, P.E., senior water resourcesengineer for URS who has been in-volved with Centennial since 2006,“existing storm sewers in the streetsaround the mall were not constructedto handle flows from the property.Runoff eventually made it into thestreet where inlets were oftenbacked up. Stormwater collectionand treatment was mandated on thedeveloper, but the Cityʼs infrastruc-ture had to be able to accept theincreased volume and convey itsafely into a natural drainage out-

fall without significantly increasingflow rates downstream.”

Transportation improvements atthe intersection of University Blvd.and Arapahoe Road would createadditional imperviousness andtherefore, runoff, but the streetreconstruction would also allow forstormwater conveyance capacity tobe upgraded as well. Stormwaterimprovements designed into theTIP include the construction of twodetention ponds to control flowsand improve water quality into BigDry Creek. The project is expectedto begin this summer. For drainagefrom the west portion of the newdevelopment, improvements in theSlaughterhouse Gulch drainageare already underway.

While URSʼ contract with theCity expired on December 31 oflast year, the firm continues to pro-vide services on The Streets AtSouthGlenn project for CURA.Completion of all infrastructure im-

provements around the new devel-opment is expected to coincide withthe new developmentʼs completion.

“The Streets At SouthGlenn isfantastic for Centennial as we moveforward,” Connor concludes. “Theproject will maximize land use andrevitalize two original anchors,Macyʼs and Sears, who have re-mained dedicated to the site duringa decade of uncertainty for thearea. The only way to really get anurban infill project like this done isto approach it in its entirety, andAlberta Development Partners hasbeen willing to make that invest-ment and has structured its plansaccordingly. Common goals for thecommon good have resulted incooperation and synergy on TheStreets At SouthGlenn. You canʼtblame us for being excited. This isreally going to be a dynamic envi-ronment.” �

Henderson-based Scott Contracting is upgrading storm sewer under Arapahoe Rd. west of Race St. for City of Centennial.

StormTechʼs system allows basins to be sized to fit specificareas. At SouthGlenn, there are six separate basins.

They knew the job was dauntingwhen they took it. Implementing

stormwater management in a fast-growing urban environment that haspreviously had few coordinatedprograms is an immediate battle onmany fronts. To get efforts and ob-jectives defined, Southeast MetroStormwater Authority looked toUrban Drainage and Flood ControlDistrict.

“Stormwater must be managedfor the common good,” statesMonica Bortolini, P.E., SEMSWAʼsFloodplain and Master PlanningProgram manager. “The value ofproperty, health of the environmentand quality of life are directly relatedto how we manage stormwater.UDFCD has championed the causeof urban stormwater since 1969.”

SEMSWA was formed in Sep-tember 2006 via an Intergovern-mental Agreement between City ofCentennial, Arapahoe County,Arapahoe County Water andWastewater Authority, East CherryCreek Valley Water and SanitationDistrict and Inverness Water andSanitation District to protect peopleand property from flooding, comply

with Federal environmental regula-tions and provide a funding mecha-nism so that stormwater services canbe performed. Following the organi-zational set-up of Urban Drainage,SEMSWA established programswith their own budgets to organizeand prioritize services provided. Toguide implementation of each pro-gram, SEMSWA utilizes both Cityof Centennial and Arapahoe CountyStorm Drainage Criteria Manuals,adopted in 2007, as well as UrbanDrainageʼs Urban Storm DrainageCriteria Manual, which has beenconsidered successful because thepolicy, planning and design aspectsenable multi-means, multi-purposeefforts that are generally supportedby data.

SEMSWA began billing forstormwater services in January2007. Fees fund efforts to addresscritical needs in construction, reme-diation and maintenance of storm-water infrastructure through plan-ning, design, inspection and moni-toring. Master plans are beingprepared in conjunction with UrbanDrainage to ensure that appropriatefacilities are constructed for current

and future development in an effortto identify regional solutions to water-shed infrastructure needs.

“Weʼre working to coordinate onthe MS4 activities with other agencypartners in the IGA,” says AshleyByerley, Land Development coor-dinator. “Thereʼs a lot of develop-ment currently underway withinSEMSWAʼs boundaries, includingthree Federal projects. Weʼre excitedto start bringing permitting and in-spection services under the sameroof with other stormwater improve-ments in our service area.”

SEMSWAʼs staff, currently total-ing 25, is chipping away at a varietyof tasks necessary to create thebase of knowledge necessary for theAuthority to perform its duties. Aninventory of infrastructure is beingprepared with GIS mapping andevaluation of condition. Floodplainsof undeveloped land are beingmapped to further facilitate devel-opment, instead of waiting fordevelopment to come knocking.Drainage problem areas are beingidentified, alternatives are beingevaluated and solutions are beingprioritized. �

With Its Ducks In A Row, SEMSWA Has Energy For Tasks Ahead