PHASE A – ALTERNATIVES ANALYSIS REPORTMajor <strong>Drainage</strong>way Planning Update for Hidden Lake-Bates Lake5.5.1 Reach H-1This reach extends from the Hidden Lake watershed headwaters, near the intersection of Carr Street <strong>and</strong> 69 thPlace to the intersection of Sheridan Boulevard <strong>and</strong> 69 th Avenue.Alternative 1: No <strong>Drainage</strong>way ImprovementsAs previously discussed, the purpose of this alternative is to maintain the existing channel <strong>and</strong> crossingstructures without implementing additional improvements to increase conveyance or improve flood proneareas. It does consider general routine, restorative <strong>and</strong> rehabilitation maintenance of the existing channel <strong>and</strong>facilities. The annual costs of maintenance have been estimated based on the facilities within the reach.Alternative 2a & 4a: Regional Detention & Water QualityThis alternative constructs a 14.5 Acft regional detention basin in the open space at the intersection ofWadsworth Blvd. & 68th Ave. (Arvada Center) & provides water quality in the detention basin. Thisdetention basin detains the 100-year storm <strong>and</strong> releases it at a rate that does not exceed the capacity of thedownstream storm sewer.Alternative 2b: Regional DetentionThis alternative converts the existing pond in Faversham Park into a regional detention basin. The pond inFaversham Park is owned <strong>and</strong> operated by the City of Westminster. Since as-built plans were not availablefor this pond, it was assumed that the pond is 5-feet deep <strong>and</strong> its entire volume is available for peak flowdetention.Alternative 3a: Improved ConveyanceThis alternative replaces the existing storm sewer pipe with new storm sewer pipe that has the capacity toconvey the 100-year storm event when also taking advantage of full flow within the street right of way in68 th Avenue between Wadsworth Boulevard <strong>and</strong> Pierce Street, in Pierce Street between 68 th Avenue <strong>and</strong>69 th Avenue, <strong>and</strong> in 69 th Avenue between Pierce Street <strong>and</strong> Sheridan Boulevard.Alternative 3b: Improved ConveyanceThis alternative replaces the existing double 4-foot by 6-foot reinforced concrete box culvert under SheridanBoulevard near the intersection of Sheridan Boulevard <strong>and</strong> 69 th Avenue with a new reinforced concrete boxculvert that has the capacity to convey the 100-year storm event without overtopping Sheridan Boulevard.Alternative 3c: Improved ConveyanceThis alternative replaces the existing 24-inch corrugated metal pipe (CMP) under the Grace Church accessroad near the intersection of Sheridan Boulevard <strong>and</strong> 69 th Avenue with a new reinforced concrete boxculvert that has the capacity to convey the 100-year storm event without overtopping the reconstructedaccess road..Alternative PlanTable 5-2: Reach H-1 Alternative Cost EstimatesStructuralImprovementsTrafficControlUtilityRelocationsPropertyAcquisitionEngineering,CM, &ContingenciesOperation &MaintenanceAlternativeTotalREACH H-1: Watershed Headwaters to Sheridan Boulevard1a Do nothing $0 $0 $0 $0 $0 $45,000 $45,0002a4a2b3a3b3c4bConstructdetention basinwith water qualityin open space atthe Arvada CenterDraft anagreement toconvert theexisting detentionbasin inFaversham Parkinto a regionaldetention basin.ConstructadditionalconveyancebetweenWadsworth Blvd.<strong>and</strong> Sheridan Blvd.Upsize box culvertunder SheridanBlvd. Raise theGrace Churchaccess road <strong>and</strong>install a boxculvert.Construct a waterquality pondupstream of theGrace Churchaccess road.$365,763 $0 $0 $0 $128,017 $30,000 $523,780$117,450 $0 $0 $0 $41,108 $7,000 $165,558$4,025,445 $201,272 $402,545 $0 $1,408,906 $40,000 $6,078,168$680,232 $102,035 $68,023 $15,585 $238,081 $17,000 $1,120,956$148,499 $0 $0 $32,315 $51,975 $4,000 $236,788Alternative 4b: Water QualityThis alternative constructs a water quality pond upstream of the Grace Church access road. The existing 24-inch CMP culvert under the Grace Church access road is undersized to convey storm flows <strong>and</strong> storm runoffponds up west of the access road, which has exp<strong>and</strong>ed the wetl<strong>and</strong>s that existed at that location prior to theconstruction of the access road. Care should be taken to protect these wetl<strong>and</strong>s when constructing a waterquality pond.5-4
48121830X1948W 76TH AV2724818242415WADSWORTH BD15122715SHERIDAN BD181836211515726018421830HiddenLake481536181524ESTES STLAMAR STCARR ST151818W 66TH AVPIERCE ST1027214212H-1: 2bFaversham Parkregional detenionHARLAN STW 74TH AVW 72ND AVW 70TH AVW 69TH AVH-1: 2a & 4aArvada Center regionaldetention with water qualityH-1: 3a100-yr storm sewerH-1: 4bWater quality atGrace ChurchH-1: 3cUpsize Grace Churchbox culvertH-1: 3bUpsize double boxculverts at Sheridan181818541821211527336124861842181818182112151815W 68TH AV1818424C a n a l181827eLegendHEC-RAS CenterlinekC r o24Major BasinSecondary BasinCounty BoundaryExisting Storm PipeInundated Building FootprintProposed Detention24Proposed ConveyanceProposed Water Quality100-Year <strong>Flood</strong>plain122424OberonLakes150 500 1,000FeetFIGURE 5-1HIDDEN LAKE REACH H-1ALTERNATIVES ANALYSIS5-530FILE: \\Tartarus\gis\gis_projects\UDFCD_Hidden_Lake\08.155.006\active\apps\HiddenLake_Reach_H-1_Map.mxd, 7/25/2008, chris_martin
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