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 LakeMeeting MinutesHidden Lake – Bates LakeMajor Drainageway Planning UpdateMonday May 19, 2008, 2:30pm – 4:00 pm at UDFCDAttendees:Ken MacKenzie UDFCD 303-455-6277 kam@udfcd.orgShea Thomas UDFCD 303-455-6277 sthomas@udfcd.orgKelly Hargadin Adams County 303-453-8766 khargadin@co.adams.co.usGeorgia Simpson City of Arvada 720-898-7646 gsimpson@arvada.orgJohn Burke City of Westminster 303-430-2400 x2126 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.comWilson Wheeler Matrix Design Group 303-572-0200 wilson_wheeler@matrixdesigngroup.comJenn Newby Matrix Design Group 303-572-0200 jennifer_newby@matrixdesigngroup.com1. PurposeReview Draft Baseline Hydrology Report2. Updated Near-Term Project Scheduled. May 23 – Baseline Hydrology Reporte. June 11 – Benefit-Cost Calculationsf. June 18 – Draft Phase A Report3. Data Gatheringg. Received at the meeting:i. Shoenberg Farms Commercial Center Drainage Reportii. Shoenberg Shopping Center – Wal-Mart Drainage Study4. Hydrologyh. Rainfall depths have increased since the 1975 study was completed.i. The C T values in CUHP have been changed since the 1975 study due to a change in the shape of thehydrograph.j. Impervious values for land use taken from the UDFCD criteria manual. Correlation of other land usetypes to imperviousness based upon actual imperviousness of similar development. Table 2-2 summarizesthe future imperviousness. Figure 2-2 shows future land use categories, Figure 2-3 shows futureimperviousness. Composite imperviousness of the 1975 study was 53.8%; current study is 56.8%.k. Variable % imperviousness for Bates Lake. Use 100% in the 100-year model. Could use less than 100%in lesser storm events.l. Some Sub-Basins are less than 90 acres. Combine basins as a check. Calibrate smaller sub-basins to bewithin 10% of the combined basins. Adjust C T , C P and Horton’s coefficients to calibrate flows.m. Comments on the draft information are due by Friday May 23. Send comments to: Tim Fairbank, with acc: to Shea Thomas.5. Alternatives Analysisn. Develop 4 to 5 alternatives per reach. Typical considerations are:i. Do nothingii. Detention (new or enhanced)iii. Improved conveyanceiv. Water quality enhancemento. Examples of reaches are:i. Hidden Lake Drainageway: Headwater to Sheridanii. Hidden Lake Drainageway: Sheridan to Lowelliii. Hidden Lake Drainageway: Adjacent to Lowelliv. Hidden Lake Drainageway: Lake Sangraco to Clear Creekv. Bates Lake Drainageway: Headwater to 60 thvi. Bates Lake Drainageway: 60 th to 58 thvii. Bates Lake Drainageway: Along future RTD Gold Line6. Websitef. Matrix to host the web site. UDFCD to provide link.g. Need to post project description, Baseline Hydrology Report, list of contacts, meeting minutes, maps,project description, schedule, and a way to get added to an information distribution list.h. Public Meeting latter half of July. Post cards need to arrive 1 week before the meeting. One week isneeded by UDFCD to compile the address list. Post public meeting notice on the web site by about July 4.i. Website will remain through project completion and a few months beyond.7. Actions Itemsp. Steering Committee Comments on Draft Baseline Hydrology Report by May 23.q. Arvada Parks & Rec Maintenance Superintendent to comment on Bates Lake if the pond fills in lesserstorm events.r. Matrix to set up website by May 23.s. Matrix to finalize Baseline Hydrology Report by May 23.t. Matrix to prepare Hydraulic Model.
PHASE A – ALTERNATIVES ANALYSIS REPORTMajor Drainageway Planning Update for Hidden Lake-Bates LakeMeeting MinutesHidden Lake – Bates LakeMajor Drainageway Planning UpdateTuesday June 3, 2008, 2:30pm – 4:00 pm at UDFCDAttendees:Ken MacKenzie UDFCD 303-455-6277 kam@udfcd.orgShea Thomas UDFCD 303-455-6277 sthomas@udfcd.orgBesharah Najjar Adams County 303-453-8770 bnajjar@co.adams.co.usGeorgia Simpson City of Arvada 720-898-7646 gsimpson@arvada.orgJohn Burke City of Westminster 303-430-2400 x2126 jburke@ci.westminster.co.usStu Williams Matrix Design Group 303-572-0200 stu_williams@matrixdesigngroup.comRobert 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.comPurpose:a. Review Baseline Hydrology Report commentsb. Review Draft Floodplain and Hydraulic Modelingc. Discuss Phase A AlternativesNear Term Schedule Upcoming Deadlinesa. June 6 – Public Meeting Invite List due from Communities to UDFCDb. June 13 – Mail Out Public Meeting Noticec. June 19 – Benefit-Cost Calculationsd. June 19 – Steering Committee Meetinge. June 25 – Draft Phase A Reportf. June 24-26 – Public Meeting (to be determined based upon site availability)g. July 9 - Comments Dueh. July 23 – Final Phase A Report1. Baseline Hydrology Report Comments from UDFCD to be addresseda. Update the tributary area in Table A-3 for Design Points 116, 117, 118, 207, 208, and 209.b. Discuss how the split flows were determined.c. Correct area and % impervious values in Table A-1 for sub-basins B2 and B3.d. Correct % impervious value for sub-basin B2 on Figure 2-5.e. The flow at Design Point 114 looks high. Verify flow is being routed and reported correctly.f. Why is there a double peak in the Hydrograph for James Baker Reservoir? The peak flow in thehydrograph is larger than the peak flow reported in Table A-3.g. UDFCD has noted problems with the current version of CUHP-2005. Once the model is fixed, UDFCDwill have Matrix re-run the hydrology with the updated model version.2. Project Websitea. The project website has been set up and is located at: http://projects.udfcd.org/hidden_lake/index.htm3. Presentation of Initial Floodplain Analysisa. Presentation of floodplain mapping and profilesi. Confirm starting elevation of Clear Creek floodplain for all profiles. Use 10-yr WSE on ClearCreek as the downstream control for the 100-yr analysis of Hidden Lake.b. Deficiencies1. Hidden Lakei.Sheridan crossing – undersized for 100-year flowii.66 th Avenue – twin 42” equivalent need to be twin 48” equivalent2. Bates Lakei.RR tracks inundatedc. Damage Assessment – inundated buildings noted on the floodplain map4. Phase A AlternativesHidden Lake WatershedReach H-1: Headwaters to Sheridan Boulevard1. Do Nothing2. Regional Detentiona. Construction detention basin in park at the intersection of Wadsworth Blvd & 68 th Ave.(Arvada Center)b. Draft agreements to convert the existing detention basin in Faversham Park into a regionaldetention basin.c. Draft agreements to convert the existing detention basins on the Wal-Mart property into aregional detention basin.3. Improved Conveyancea. Construct additional conveyance between Wadsworth Blvd. and Sheridan Blvd.b. Upsize the box culvert under Sheridan Blvd. to increase capacity.c. Raise the Grace Church access road and install a box culvert under it.4. Water Qualitya. Provide water quality in the bottom of the detention basin proposed in Alternative 2a.b. Construct a water quality pond upstream of the Grace Church access road.Reach H-2: Hidden Lake1. Do Nothing2. Water Quality - Construct a fore-bay east of Sheridan Blvd, south of 69 th Ave.Reach H-3: Lowell Blvd. between Hidden Lake & Lake Sangraco1. Do Nothing2. Improved Conveyancea. Upsize the elliptical pipes under 66 th Ave to a box culvert.b. Replace 96” CMP if needed due to corrosion and abrasion3. Water Quality - Remove the low flow concrete channel and replace with a buried soil riprap lined lowflow channel and water quality check structures.Reach H-4: Lake Sangraco to Clear Creek.1. Do Nothing2. Water Quality - Revise the 96-inch RCP outlet to have low flows discharge into a fore-bay north of62 nd Ave.
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