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HomeMy WebLinkAboutSite Certifications - 04/07/2016Page 1 of 3 1315 Oakridge Drive – Suite 120 Fort Collins, CO 80525 ditescoservices.com Delivery by email to ekeeton@fcgov.com March 7, 2016 Revised April 2, 2016 Ms. Erika Keeton, PE City of Fort Collins – Engineering Department 281 North College Ave. Fort Collins, 80524 RE: MAX BRT Stormwater Pond Volume Verification Dear Erika: This letter and attachments contain information related to your request to analyze the overall as-built detention pond volume for various facilities across the MAX Bus Rapid Transit corridor. Volumetric analysis was performed to compare design and as-built pond volumes for the Harmony (bioretention), Mason Street Outfall (MSO), Downtown Transit Center (DTC), and University Plaza ponds. Background A drainage report for the Mason Corridor MAX Bus Rapid Transit Project was prepared by Michael Baker Jr., Inc and submitted to the City on November 15, 2011. In this report water quality and pond volumetric calculations were performed for the entire project site. This letter report compares all pond information to that contained in the original report. Construction sheets showing each location can be found in Appendix A of this report. Water Quality Pond #1 - Harmony Outfall The drainage report states “The Harmony Outfall conveys drainage flows from basins B1.0, B1.1, B1.2, and B1.3. Water quality treatment for basins B1.0, B1.1, and B1.2 is provided by a porous landscape detention (PLD) pond. Basin B1.3 is not treated for water quality due to depth limitations at the outfall to the PLD and zero increase to the impervious area to this basin.” Appendix E (Hydrology and Water Quality Requirements) of the drainage report provides for pond volumetric calculations. The report uses the prismoidal method to calculate pond volume storage. The Harmony Outfall pond was designed with a total volume of 1,679 cubic feet at the 5,042 elevation stage (Appendix B). An as-built survey of the pond was performed by the City of Fort Collins on June 11, 2014 and subsequently modeled in Autodesk Civil3D. Using similar methodology to the drainage report to calculate pond volume, storage of the Harmony Outfall pond was shown to have a total volume of 1,415 cubic feet at the 5,042 elevation stage (Appendix C). This as-built volume accounts for 84.3% of the designed volume. The actual water quality volume provided versus the calculated is approximately 749 cubic feet and 534 cubic feet respectively. Efforts were made to accommodate all new construction drainage design criteria. However, considering this project was a large scale transportation corridor improvement project retrofit parallel to an existing heavy rail freight corridor, some criteria could not be reasonably met due to existing site constraints. Page 2 of 3 Water Quality Pond #2 MSO Outfall The drainage report outlines that “The Mason Street Outfall (MSO) conveys drainage flows from basins F1.0 through F1.11 and the future connections of the CSU Motor Pool Parking Lot, CSURF Parking Lot, and CSU Parking Lot to a proposed 60-inch outfall at the existing BNSF Pond/Floodway. Stormwater quality treatment for these basins is provided via a proposed extended detention basin located within the Spring Creek FEMA floodway.” As noted above, Appendix E (Hydrology and Water Quality Requirements) of the drainage report provides for pond volumetric calculations. The report uses the prismoidal method to calculate pond volume storage. The MSO Outfall pond has a total volume of 142,906 cubic feet at the 4,990 elevation stage (Appendix B). An as-built survey of the pond was performed by the City of Fort Collins on June 11, 2014 and subsequently modeled in Autodesk Civil3D. Using similar methodology to the drainage report, pond volume storage of the MSO Outfall has a total volume of 154,037 cubic feet at the 4,990 elevation stage (Appendix C). This as-built volume accounts for 107.8% of the designed volume. Please note this particular pond was verified by Michael Baker at the conclusion of the BRT project. Water Quality Pond #3 DTC Outfall The drainage report notes that “The Downtown Transit Center (DTC) is located at the intersection of South Mason Street and Maple Street. Improvements for this location include the construction of an off-ramp from the BRT in South Mason Street to the existing DTC parking area on the southeast corner of the intersection. An existing detention/water quality pond is affected by the construction of this ramp which accounts for an additional 0.04 acres of impervious area. In accordance with the Downtown Transit Center Final Drainage & Erosion Control Study, dated August 2000, prepared by Nolte Associates, Inc. the existing pond was designed to detain and provide stormwater quality treatment for 1.38 acres developed area at 75% imperviousness. The existing pond volumes for stormwater quality treatment and 100-yr storage are 0.041 acre-feet and 0.131 acre-feet, respectively. The existing grading of the pond contained the stormwater quality treatment volume within the footprint of the pond with the 100 year water surface extending into the DTC parking lot at an elevation of 4980.74-feet. As part of the BRT improvements for this area, it is proposed that the existing pond be re-graded in order to make up for the volume lost and the increased impervious area due to the proposed improvements. The proposed DTC pond treats approximately 1.43 acres at 76% imperviousness. The calculated water quality treatment and 100-year storage volumes are 0.043 acre-feet and 0.131 acre-feet, respectively. The proposed grading for the DTC pond contains the water quality treatment volume solely within the footprint of the pond, with the 100-year water surface extending into the existing DTC parking lot at an elevation of 4980.72-feet. The existing outfall structure for the pond will not need to be altered.” As stated in the drainage report, the proposed grading for the DTC pond contains the water quality treatment volume solely within the footprint of the pond, with the 100-year water surface extending into the existing DTC parking lot at an elevation of 4980.72-feet. As the as-built topography did not contain areas of parking lot space adjacent to the pond, a comparison 100 year volume could not be provided. Regardless, this comparison is not needed as the only change to the pond was to occur through water quality volumes as shown above (comparing 0.041 ac-ft to 0.043 ac-ft). Comparatively, the design volume for water quality was 1,883.6 cubic feet at stage 4979.90. As-built water quality volume is 1,905.02 cubic feet or 101% of design volume. Page 3 of 3 University Plaza Outfall The drainage report states “The University Plaza Outfall conveys drainage flows from basins E2.0 and E2.1 to an existing 30-inch storm sewer in South College Avenue. The City does not have any existing design information for this line; however, there has been no documented surcharging of the system according to the City's maintenance crew's.” Sheet No. 284 of the Drainage Site Plan references to see the stormwater management plans on sheet EC37 and EC38 for full pond grading extents. These sheets call out that the grading of the pond is to increase the pond capacity by 2,240 cubic feet. Sheets EC37 and EC38 do not show any proposed grades at this location. Nowhere in the drainage report are flows from the BRT being routed to this pond. As such, we see no need to increase the pond volume as noted in the drawings. It appears as though there was confusion at the end of the project relative to the drainage design in this reach of the project. Regardless, a survey of the pond was performed and modeled. The pond volume storage of the University Plaza Outfall has a total volume of 15,717 cubic feet at the 5,017.5 elevation stage (Appendix C). Engineer’s contact information: Keith Meyer, PE Ditesco, LLC Name Company Name Keith.Meyer@ditescoservices.com 1315 Oakridge Drive, Suite 120; Fort Collins, CO 80525 Email Address Physical Address 970-988-8605 Telephone Number Please let me know if you have any questions or require further information regarding this report, I can be reached by phone at 970.988.8605 and email keith.meyer@ditescoservices.com. Sincerely, Keith Meyer, P.E. Enc. Appendix A – Construction Sheets Appendix B – Drainage Report Water Quality Pond Volume Calculations Appendix C – As-Built Water Quality Pond Volume Calculations STSTSTSTSA 1"=20' JPC NJM DRAINAGE N/A DE04 PROPOSED DRAINAGE BASIN MAP DE04 of 56 40'20' MASON CORRIDOR BRT C1-302 MINOR BASIN LINE MAJOR BASIN LINE STORM SEWER CONTOUR EMERGENCY OVERFLOW EXISTING PROPOSED BASIN LABEL DESIGN POINT PROPOSED DRAINAGE BASIN LEGEND DRAINAGE DITCH 10YR COEFFICIENT 100YR COEFFICIENT BASIN ACREAGE BASIN DESIGNATION APPENDIX A SASASA 12' 3' MIN. 5' 1"=20' JRS JRS DRAINAGE N/A DRAINAGE DETAILS MSO POND B23B24B25B26B27B28 B29 B30 B31 B32 B33 B34 B35 B36 B37 B21 B22 B1 B3 B2 B4 B6 B7 B5 B8 B9 B10 B11 B12 B13 B15 B16 B17 B18 B19 B20 B38 B41 B42 B43 FOREBAY D87 MICROPOOL 20'40' B14 B40 GRADE BREAK WQ WSEL = 4988.33' WINGWALL PER FTC D-19A AND D-19B GRADE BREAK B45 B46 B47 SPILLWAY ACCESS TRAIL B48 B49 B50 B51 B52 73LF ~ 30" RCP B39 B44 3443 SY CLAY POND LINER 492 SY TURF REINFORCEMENT MAT TOP OF POND EL=4992.0 2:1 HOMOGENOUS FILL EXIST. GROUND COMPETENT BEDROCK D86 of 104 D92 STA: 175+62.02, 315.20' LT CENTER OF HEADWALL WITH FLAP GATE APPENDIX A 2' 4' 2' 1. 5 ' 6' 0. 5 ' 6" Numbers Structure No Revisions: Revised: Void:Sheet Subset: Detailer: Designer: Sheet NumberSubset Sheets: Init.CommentsDate: R-X Sheet Revisions9/27/2011Print Date: Horiz. Scale: 7073-BRT_Drainage_Details05-DTC_Pond.dgn Unit Leader Initials File Name: Unit Information ev a u g h n 1 1 : 2 5 : 1 7 A M c : \ p w v 8 i - l o c a l \ b a k e r _ p r o j e c t s \ e v a u g h n \ d m s 9 5 1 5 8 \ 7 0 7 3 - B R T _ D r a i n a g e _ D e t a i l s 0 5 - D T C _ P o n d . d g n Vert. Scale:Ft. Collins: 7073 Project No.MASON CORRIDOR BRT 281 NORTH COLLEGE AVENUE FORT COLLINS, CO 80522 970.221.6605 165 S. UNION BLVD., STE. 200 LAKEWOOD, CO 80228 720.514.1100 Construction Drawings C1 - 3 0 2 C1-302 0'10'20' 1"=10' JPZ TOB DRAINAGE CURB CUT CUT OFF WALL FINISHED POND GRADE RIP RAP TYPE M, D50 = 12" A B MATCH EXISTING FINISHED POND GRADE 100 YR WSE = 4980.72' NORTHING EASTING ELEVATION NORTHING EASTING ELEVATION NORTHING EASTING ELEVATION B1 132328.57 194311.69 4981.55 C2 132270.98 194332.23 4979.25 S9 132214.48 194282.73 4980.88 B2 132328.73 194353.73 4979.50 C3 132277.82 194334.69 4979.16 S10 132219.40 194286.13 4980.65 B3 132277.66 194355.92 4979.58 C4 132285.02 194334.51 4979.08 S11 132224.36 194289.46 4981.08 B4 132264.71 194354.17 4979.66 C5 132291.72 194333.04 4979.00 S12 132229.97 194294.73 4980.81 B5 132258.74 194343.08 4979.58 C6 132304.91 194330.44 4978.85 S13 132267.53 194300.84 4982.54 B6 132248.49 194319.51 4979.60 C7 132308.07 194328.58 4978.80 S14 132196.23 194294.47 4982.12 B7 132241.59 194304.18 4980.01 C8 132309.19 194325.30 4978.76 S15 132201.41 194297.46 4981.32 B8 132263.69 194308.72 4979.81 S1 132220.44 194274.15 4981.19 S16 132206.06 194301.29 4981.05 B9 132276.37 194311.10 4979.68 S2 132225.38 194277.49 4981.21 S17 132209.91 194305.79 4981.34 B10 132287.94 194312.10 4979.90 S3 132228.89 194279.94 4981.26 S18 132196.63 194303.25 4981.96 B11 132298.98 194312.98 4979.23 S4 132234.86 194282.44 4981.36 S19 132201.26 194307.05 4981.69 B12 132304.13 194316.16 4979.60 S5 132269.74 194288.78 4982.86 S2 132194.67 194305.51 4981.52 B13 132314.12 194316.32 4979.97 S6 132218.76 194276.57 4981.52 S21 132199.27 194309.26 4981.25 B14 132326.38 194320.05 4979.13 S7 132223.65 194279.96 4981.16 S2 132212.71 194317.39 4981.01 B15 132313.48 194336.30 4979.00 S8 132209.56 194279.27 4981.61 S2 132262.36 194358.53 4980.65 132255.72 194323.58 4979.45 S9 132214.48 194282.73 4980.88 MATCH EXISTING (S23) #4 REBAR @ 12" OC SPACING (TYP.) 1"=1' C1 Bay f a r m Pro s p e c t Un i v e r s i t y Lau r e l Mu l b e r r y Oliv e Mo u n t a i n DT C LOCATION MAP MATCH EXISTING AT S5 AND S13 DRAINAGE DETAILS DOWNTOWN TRANSIT CENTER (DTC) POND SCALE: 1:1 SCALE: 1:1 FINISHED POND GRADE A D89 BD8 9 BD8 9 A D89 3: 1 3: 1 3:1 3:1 10: 1 2.7 % 2.2 % 2.7 % 2% B7 C1 B8 B9 C2 C3 C4 C5 C6 C7 C8 B1 B2 B3 B4 B5 B10 B11 B12 B13 B14 B15 4980 4981 R 2 0 ' R 5 ' S6 S1 S2 S3 S4 S5 S7 S9 S8 S10 S11 S12 S13 S14 S15 S16 S17 S18 S19 S20 S21 S22 POND BOTTOM SWALE POND GRADE BREAK B6 WQ WSE= 4979.90' 1 SCALE: 1"=10' PLAN SECTION SECTION MATCH EXISTING GRADE AT OUTLET STRUCTURE CLASS 6 GRANULAR BEDDING 6" DEPTH RIP RAP TYPE M, D50 = 12" (D50=2' DEPTH) CLASS 6 GRANULAR BEDDING 6" DEPTH D89 of 104 APPENDIX A Water Quality Pond #1 Harmony Outfall Project Name:Ft Collins BRT Michael Baker Project No: 118857 Revised Date:03/16/11 Calculated By: JPZ Checked By: JPZ Approved By: JPZ WQ Volume Requirement WQ VOL=(WQCV/(12))*AREA*1.2 Tributary Basins WQCV 0.24 WQ VOL:0.017 acre-feet B1.0 0.13 98%749.46 cubic feet B1.1 0.49 76% B1.2 0.11 38% 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 HARMONY OUTFALL 0 0 0 0 POND ELEV AREA VOLUME VOLUMEsum VOLUMEsum METHOD 0 0 DESIGNATION (ft2)(ft3)(ft3)(acre-ft) WQCV=0.8*((0.91*i 3)-(1.19*i2)+(0.78*i)) Area (Acres) Impervious % Pond Volume Calculations () 3 2121 DepthAAAA V ++= 0 0 DESIGNATION (ft )(ft )(ft )(acre-ft) 0 0 5040.99 1 0 0 0.00 0 0 5041 1,199 4 4 0.00 0 0 5041.2 1,370 257 261 0.01 0 0 5041.4 1,556 292 553 0.01 0 0 5041.6 1,756 331 884 0.02 0 0 5041.8 1,972 373 1,257 0.03 0 0 5042 2,253 422 1,679 0.04 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Totals 0.72 75% WQ WSE: 5041.52 ft HA R M O N Y O U T F A L L pr i s m o i d a l () 3 2121 DepthAAAA V ++= APPENDIX B Water Quality Pond #2 MSO Outfall Project Name:Ft Collins BRT Michael Baker Project No: 118857 Revised Date:07/08/11 Calculated By: JPZ Checked By: JPZ Approved By: JPZ WQ Volume Requirement WQ VOL=(WQCV/(12))*AREA*1.2 Tributary Basins WQCV 0.32 WQ VOL:2.019 acre-feet F1.0 0.18 94%87951.37 cubic feet F1.1 0.42 100%Vforebay:0.06 acre-feet Qforebay:8.80 CFS F1.2 0.36 0%Dforebay pipe: F1.3 0.16 98%VBS:264 cubic feet F1.4 0.56 85% F1.5 0.42 0% F1.6 0.35 77% F1.7 0.45 95% F1.8 0.69 81% F1.9 0.50 0% F1.10 0.02 100% F1.11 0.04 100%MSO POND CSU MOTOR POOL 10.10 76% CSU UNIVERSITY SQUARE PARKING LOT 8.60 90%POND ELEV AREA VOLUME VOLUMEsum VOLUMEsum METHOD CSURF PARKING LOT 7.40 90%DESIGNATION (ft2) (ft3) (ft3)(acre-ft) LAKE AND CENTER 24.20 78%4980.407 1 0 0 0.00 BNRR AND PROSPECT 6.20 90%4981 595 123 123 0.00 GRIFFIN PLAZA 3.13 24%4982 688 641 764 0.02 WQCV=1.0*((0.91*i3)-(1.19*i2)+(0.78*i)) Area (Acres) Impervious % Pond Volume Calculations () 3 2121 DepthAAAAV++= GRIFFIN PLAZA 3.13 24%4982 688 641 764 0.02 4983 695 691 1,455 0.03 4984 3,723 2,009 3,464 0.08 4985 11,935 7,441 10,905 0.25 4986 21,191 16,343 27,248 0.63 4987 25,330 23,230 50,478 1.16 4988 29,475 27,376 77,854 1.79 4989 32,510 30,980 108,835 2.50 4990 35,657 34,071 142,906 3.28 Totals 63.78 78% WQ WSE: 4988.33 ft FOREBAY A Required(ft2) H (ft) C 2g (ft/s2) 1.70 1.083333333 0.62 64.4 W (in) H (in) A Design (ft2) 24 10 1.67 OVERFLOW INLET Q (cfs) A Required(ft2) H (ft) C 2g (ft/s2) 126 8.77 8.3333 0.62 64.4 DIA (in) A Design (ft2) 42 9.62 MS O P O N D pr i s m o i d a l () 3 2121 DepthAAAAV++= APPENDIX B Water Quality Pond #3 DTC Outfall Project Name:Ft Collins BRT Michael Baker Project No: 118857 Revised Date:03/16/11 Calculated By: JPZ Checked By: JPZ Approved By: JPZ WQ Volume Requirement WQ VOL=(WQCV/(12))*AREA*1.2 Tributary Basins WQCV 0.30 WQ VOL:0.043 acre-feet EX TRIBUTARY 1.38 75%1883.60 cubic feet NEW BRT IMP 0.04 100%100-YR VOL:0.131 acre-feet 5706.36 DTC POND POND ELEV AREA VOLUME VOLUMEsum VOLUMEsum METHOD DESIGNATION (ft2)(ft3)(ft3)(acre-ft) WQCV=1.0*((0.91*i 3)-(1.19*i2)+(0.78*i)) Area (Acres) Impervious % Pond Volume Calculations () 3 2121 DepthAAAA V ++= DESIGNATION (ft )(ft )(ft )(acre-ft) 4978.7 1 0 0 0.000 4978.8 34 1 1 0.000 4979 337 32 33 0.001 4979.2 965 125 158 0.004 4979.4 1,955 286 444 0.010 4979.6 2,889 481 926 0.021 4979.8 3,239 612 1,538 0.035 4980 3,599 683 2,222 0.051 4980.2 4,109 770 2,992 0.069 4980.4 4,764 886 3,878 0.089 4980.6 5,773 1,052 4,930 0.113 4980.8 7,066 1,282 6,212 0.143 Totals 1.43 76% WQ WSE: 4979.90 ft 100-YR WSE: 4980.72 ft DT C P O N D pr i s m o i d a l () 3 2121 DepthAAAA V ++= APPENDIX B APPENDIX C As-Built Water Quality Pond Volume Calculations Water Quality Pond #1 Harmony Outfall As-Built Civil 3D Pond Volume Calculations Pond Designation Elevation Area (ft^2) Volume (ft^3) Volume_Sum (ft^3) Volume_Sum (acre-ft) Method HA R M O N Y O U T F A L L 5,041.0 48 0 0 0.000 Pr i s m o i d a l 5,041.2 1,151 96 96 0.002 5,041.4 1,439 258 354 0.008 5,041.5 1,565 180 534 0.012 5,041.6 1,649 129 663 0.015 5,041.8 1,890 354 1,016 0.023 5,042.0 2,101 399 1,415 0.032 5,042.2 1,565 365 1,780 0.041 5,042.4 988 253 2,033 0.047 5,042.6 413 136 2,169 0.050 5,042.8 94 47 2,216 0.051 5,043.0 59 15 2,232 0.051 5,043.2 136 19 2,250 0.052 5,043.4 76 21 2,271 0.052 APPENDIX C As-Built Water Quality Pond Volume Calculations Water Quality Pond #2 MSO Outfall As-Built Civil 3D Pond Volume Calculations Pond Designation Elevation Area (ft^2) Volume (ft^3) Volume_Sum (ft^3) Volume_Sum (acre-ft) Method MS O O U T F A L L 4,981 646 0 0 0.000 Pr i s m o i d a l 4,982 706 676 676 0.016 4,983 763 734 1,410 0.032 4,984 4,443 2,349 3,759 0.086 4,985 11,477 7,687 11,446 0.263 4,986 20,852 15,933 27,379 0.629 4,987 26,279 23,513 50,892 1.168 4,988 32,868 29,512 80,404 1.846 4,989 37,036 34,931 115,335 2.648 4,990 40,390 38,701 154,037 3.536 4,991 43,805 42,086 196,123 4.502 4,992 38,744 41,249 237,371 5.449 4,993 29,363 33,945 271,316 6.229 4,994 4,661 15,241 286,557 6.578 4,995 316 2,064 288,621 6.626 4,996 37 154 288,775 6.629 APPENDIX C As-Built Water Quality Pond Volume Calculations Water Quality Pond #3 DTC Outfall As-Built Civil 3D Pond Volume Calculations Pond Designation Elevation Area (ft^2) Volume (ft^3) Volume_Sum (ft^3) Volume_Sum (acre-ft) Method DT C O U T F A L L 4,978.8 57.76 0 0 0.000 Pr i s m o i d a l 4,979.0 803.64 72 72 0.002 4,979.2 1,623.30 238 310 0.007 4,979.4 2,147.27 376 686 0.016 4,979.6 2,392.67 454 1,139 0.026 4,979.8 2,585.41 498 1,637 0.038 4,980.0 2,779.00 536 2,173 0.050 4,980.2 2,973.61 575 2,749 0.063 4,980.4 3,167.81 614 3,363 0.077 4,980.6 3,371.50 654 4,016 0.092 4,980.8 3,557.52 693 4,709 0.108 4,981.0 3,769.23 733 5,442 0.125 4,981.2 3,733.52 750 6,192 0.142 4,981.4 3,479.96 721 6,913 0.159 4,981.6 3,294.80 677 7,591 0.174 4,981.8 3,088.95 638 8,229 0.189 4,982.0 385.14 304 8,533 0.196 4,982.2 144.62 51 8,584 0.197 4,982.4 47.22 18 8,603 0.197 4,982.6 1.44 4 8,606 0.198 Theoretical 100­year pond volume highlighted without topography in parking lot area. APPENDIX C As-Built Water Quality Pond Volume Calculations Water Quality Pond University Plaza Outfall As-Built Civil 3D Pond Volume Calculations Pond Designation Elevation Area (ft^2) Volume (ft^3) Volume_Sum (ft^3) Volume_Sum (acre-ft) Method UN I V E R S I T Y P L A Z A O U T F A L L 5,014.50 6 0 0 0.000 Pr i s m o i d a l 5,015.00 2296 402 402 0.009 5,015.50 8705 2579 2,981 0.068 5,016.00 11813 5110 8,091 0.186 5,016.50 7903 4896 12,987 0.298 5,017.00 1464 2128 15,115 0.347 5,017.50 958 601 15,717 0.361 5,018.00 666 404 16,120 0.370 5,018.50 199 205 16,325 0.375