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

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