Phase A - Alternatives Analysis Report - Urban Drainage and Flood ...

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PHASE A – ALTERNATIVES ANALYSIS REPORTMajor Drainageway Planning Update for Hidden Lake-Bates LakeAttendees:Ken MacKenzieMark OmotoGeorgia SimpsonJohn BurkeRobert KrehbielTim FairbankStu WilliamsLarry & Karen StineWayne HardinKenneth & Xyla WagnerFred KissellDiann KissellRon YankerDick LaidleyDona ChurchwellEleaner ScottAnthony ElliotRick MayoTom KotmalGeoff RosePat DaleyLois & Dave GraberDavid FerlieMike LitzanCarla RemboltDon HillsGeorge ClarkGladus ElliottHeidi KaplinPeter RomanyshynTom BrossSandy FlemingMeeting MinutesHidden Lake – Bates LakeMajor Drainageway Planning UpdateThursday June 25, 2008, 6:30pm – 8:00 pmUDFCDAdams CountyCity of ArvadaCity of WestminsterMatrix Design GroupMatrix Design GroupMatrix Design Group4534 W. 65 th Ave.4147 W. 64 th Ave.8530 Cedar Ln.4779 W 68 th Ave.4779 W. 68 th Ave.2800 Cottonwood Dr.6396 Otis St.6787 Faton St.6650 Quitman Ct.6231 Lowell Blvd.5130 W. 69 th Pl.6862 Wyman Way6749 Quay St.3196 W. 62 nd Ave.6340 Chase6725 King5005 W. 60 th Ave.6787 Eaton St.5933 Willowbrook Ct.6100 N. Federal Blvd.6261 Lowell Blvd.4731 W. 66 th Ave.6511 W. 72 nd Dr.6469 Xavier St.7432 Saulsbury St.Purpose:Inform the community about the stormwater hydrology, hydraulics and sewer improvement alternatives that are beingconsidered as part of the Hidden Lake – Bates Lake Major Drainageway Planning Update for the Urban Drainage &Flood Control District, as well as the local community sponsors of the City of Arvada, City of Westminster andAdams County.6. Introductionsa. Ken MacKenzie introduced the local sponsors and consulting engineers.7. Project purposea. Ken MacKenzie described the purpose of updating the Major Drainageway Planning study for HiddenLake and Bates Lake, which was originally done in 1975, and he also described the benefits this studywill provide to the community.8. Updated Hydrologya. Tim Fairbank described that an updated hydrologic analysis needed to be preformed on thewatersheds within the study area because there has been many physical changes in the watershedsince the last Major Drainageway Planning Study was done in 1975.9. Floodplain Analysisa. Robert Krehbiel described how the floodplains were developed along the main stem flowpaths for theHidden Lake and Bates Lake watersheds.b. The purpose of developing floodplains is not to re-map any regulatory floodplains in the area but toidentify areas that could flood in the future so that alternatives can be proposed to eliminate or reducepotential flooding.10. Main Stem Reachesa. Tim Fairbank described the extents of the six individual reaches, along the Hidden Lake and BatesLake main stem flowpaths, within the study area. (H-1, H-2, H-3, H-4, B-1 and B-2)11. Possible Alternativesa. Tim Fairbank went through the five categories of alternatives that were considered in the alternativesanalysis. (Do Nothing, Regional Detention, Improved Conveyance, Water Quality, and Combinationof Alternatives)b. Tim Fairbank also went through each of the specific alternatives that have been investigated as part ofthis Phase A – Alternatives Evaluation report.12. Public Commentsa. Are climate adjustments taken into consideration when performing the hydrologic analysis? It wasdescribed that hydrology is based on past events and therefore historical climatization is taken intoaccount when rainfall values that were used in the study were established by UDFCD.b. What water feeds Hidden Lake? A member of the community described that Juchem Ditch feeds intoHidden Lake. Also storm runoff, water from washing of cars, and water from over-watering lawnsalso feed the lake.c. When the 96” CMP storm pipe was installed in Lowell Blvd., the spring and well on a resident’sproperty near Lowell Blvd. and 62 nd Ave reportedly dried up. Care will be taken when working ingroundwater to not alter historic condition if any work is completed on this pipe. No construction willbe completed under this study project.d. There is a concern as to the capacity of the trash rack upstream of the 96” in Lowell Blvd. Trashracks are not necessary on pipes over 4 feet in diameter if daylight can be seen through the culvert. Ifthese conditions cannot be met, then current design standards for trash racks are to haveapproximately 4 times the capacity of the pipe.e. Are there any immediately planned improvements to Lowell Blvd? Mark Omoto described streetimprovements planned for Lowell Blvd. between 62 nd Ave and 68 th Ave. The suggestion was made toinstall a new pipe in the street as the same time the street improvements are being done if possible.f. It was brought to the group’s attention that the 96” pipe in Lowell Blvd. discharges to Aloha Lakenorth of Lake Sangraco and not Lake Sangraco itself. There is a concern that high flows into eitherAloha Lake or Lake Sangraco, the houses to the north of the lake could be flooded. Since the houseswere built after modifications were made to Lake Sangraco and after James Baker Reservoir was builtthey should have been required to be built above the 100-year floodplain per current developmentcriteria.g. A concern was raised that with the installation of James Baker Reservoir that the flooding of LakeSangraco could be worse because the James Baker Reservoir spillway discharges to Lake Sangraco.Since James Baker Reservoir is a major facility and was built recently it should have been arequirement during the design to look into what would happen to the downstream Lake Sangraco if
PHASE A – ALTERNATIVES ANALYSIS REPORTMajor Drainageway Planning Update for Hidden Lake-Bates Lakethe James Baker Reservoir were to overtop. James Baker Reservoir contains the 100-year storm eventfrom the basin.h. Are there any flooding issues near Federal Blvd? That area is not adjacent to either of the main stemflowpaths so no detailed hydraulic model was developed in that area. No flooding issues wereidentified in that area as part of this study. Pipes have been recently added to 64 th Ave.i. The suggestion was made to crush up the existing concrete low flow channel adjacent to Lowell Blvdand use the concrete as riprap for the channel bank lining if the water quality alternative of removingthe concrete low flow channel is proposed.j. The suggestion was made to install a wetland pond as the forebay upstream of Hidden Lake east ofSheridan Blvd.k. The concern was raised that designing storm drains for a 2 or 5-year storm event is not conservativeenough. Current design criteria in Arvada is to design the pipe for the 3½ year storm and have theroads convey any additional flow.l. A concern was raised about a lack of maintenance of facilities after they are constructed. It wasdescribed that quite a few State restrictions have been put on local communities regardingmaintenance when they discharge to Waters of the US, such as Clear Creek. If facilities are designedand built per current criteria, they can be declared “maintenance eligible” by UDFCD. UDFCD willmaintain them on behalf of the local community.Meeting MinutesHidden Lake – Bates LakeMajor Drainageway Planning UpdateThursday July 15, 2008, 2:00pm – 4:00 pm at UDFCDAttendees:Ken MacKenzie UDFCD 303-455-6277 kam@udfcd.orgShea Thomas UDFCD 303-455-6277 sthomas@udfcd.orgGeorgia Simpson City of Arvada 720-898-7646 gsimpson@arvada.orgJohn Burke City of Westminster 303-658-2126 jburke@ci.westminster.co.usRobert Krehbiel Matrix Design Group 303-572-0200 robertk@matrixdesigngroup.comTim Fairbank Matrix Design Group 303-572-0200 tim_fairbank@matrixdesigngroup.comJenn Newby Matrix Design Group 303-572-0200 jennifer_newby@matrixdesigngroup.comGeorge Kast Hidden Lake OwnerAlan Gillan Aloha Beach Ownerj. George Kast was concerned about any changes, due to this study, that would affect his ability toconstruct a development along the north shore of Hidden Lake. No new restrictions on developmentwill be imposed due to this study.14. Draft Phase A Commentsa. A list of the formal comments and resolutions are included on the attached spreadsheet.b. Additional comments to those formally submitted.i. The formal name of James Baker Reservoir is “Jim Baker Reservoir”. Change the name onall of the exhibits and in the Phase A report.ii. Make the Phase A report a double sided document.iii. Include the jurisdictional boundaries on the Study Area Map.iv. Submit all of the copies of the Final Phase A report to Ken on July 29 th .15. Resolutionsa. Overalli. Model the hydraulics of the recommended plan and show the proposed floodplain on Figures7-1 through 7-6.b. Reach H-1i. Keep the proposed box culvert under the Grace Church access road a double 3.5’ x 10’ boxculvert. This culvert has the 100-year capacity and is easier to maintain than the currentlyproposed double 2.5’ x 10’ box culvert.ii. Include property acquisition costs for the box culvert under the Grace Church access road.c. Reach H-2i. Change the proposed forebays in Reach H-2 to a water quality wetland.ii. Remove the restaurant over Hidden Lake from the “Inundated buildings” hatching.d. Reach B-1i. Review options for water quality in the Bates Lake improvements. The existing low flowsbypass this lake. Parks and the community may be concerned with standing water for 40hours. It may not be possible to retrofit this Park with water quality.Purpose – Review Draft Phase A Report commentsu. Meet the owners of Hidden Lake and Aloha Beachv. Discussions about the operation of Hidden Lakew. Address Phase A CommentsNear Term Schedule Upcoming Deadlinesi. July 29 – Final Phase A Reportj. August 26 – Selection of Preferred Alternative13. Update on Lake Operationh. Hidden Lake has a total volume of 2,200 Acft.i. Lake L’Nor and Lake Pompano are the lakes north of Aloha Beach Lake.
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