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Home My WebLink AboutDrainage Reports - 05/01/1990MOINC Engineering Consultants 2900 South College Avenue Fort Collins, Colorado 80525 303/226-4955 April 13, 1990 Ms. Susan D. Hayes Stormwater Utility Department City of Fort Collins P.O. Box 580 Fort Collins, Colorado 80522 RE: OAKRIDGE WEST - SECOND FILING - SUPERTOTS LEARNING CENTER FINAL DRAINAGE REPORT - REVISED Dear Susan, RBD Inc. is pleased to submit this letter and accompanying cal- culations and Drainage and Grading Plan as the final drainage report for the Oakridge West Second Filing, a planned unit development, proposed by the Everitt Companies. This 1.14 acre site is located within the McClellands Major Drainage Basin of South Fort Collins, Colorado, as shown in the vicinity map (Figure 1). It is bounded on the east by Lemay Avenue, on the north by the Evangelical Covenant Church, and on the west and south by undeveloped property. The site presently is covered with field stubble and natural grasses, and slopes in a southeastern direction where it drains into an existing storm drain inlet at the northwest corner of Lemay Avenue and Rule Drive. A ditch running along Lemay Avenue also crosses the site which conveys present stormwaters north of the site (refer to Figure 2). The project site has been divided into two sub -basins (Basins A & B) as shown on the Drainage and Grading Plan. A composite runoff coefficient "C" was calculated for each sub -basin and used in computing the runoff and the storage detention. The Mass Diagram Method was used to compute the storage volumes for each basin. The ponding area west of the building and the parking lot area will provide the storage volume for Basins A and B, respectively. The Detention Pond Information Table on the Drainage and Grading Plan summarizes the storage volume analyses. This site has been included in the area recently analyzed in the Master Drainage Study For The Oakridge Business Park (by RBD, Inc.) which was submitted to the City of Fort Collins for review in March 1990. This study was completed in cooperation with the Stormwater Utility Department staff and recommends that this area not be required to provide staged detention. Based on the fact Other Offices: Vail, Colorado 303/476-6340 • Colorado Springs, Colorado (719) 598-4107 this study will likely be tion volumes and outflow based on a 0.5 cfs/acre rates were calculated to Pond B. These release proposed 30" storm drain approved in the near future, the deten- release rates for this development were release rate. These outflow release be 0.21 cfs for Pond A and 0.37 cfs for outflows are then discharged into a pipe. Realizing that the remote chance that the drainage report referenced above may not be approved by the completion of construction, provisions have been made it restrain flows to the YL 0.2 cfs/acre rate. These provisions consist of resizing the orifice openings and allowing deeper ponding depths. Ponding depths in both areas will still be under 1.2 feet. Notes have been added to the plan requiring the contractor to confirm the orifice sizing before installing the orifice plates. Offsite flows include the runoff from the basin areas north and west of the site (refer to Figure 2). Runoff flows from the north have been previously calculated in the Harmony Market P.U.D. Filing One Final report (revised 4/89 by RBD, Inc.) to be 15.8 cfs for the 100 year historic storm (which is greater than the, 100 year developed storm). The runoff from the church site was calculated to be 1.7 cfs for the 100 year developed storm found in the Storm Drainage Report For The Evangelical Covenant Church P.U.D. - Phase 1, dated March 29, 1985 by James H. Stewart and Associates, Inc. Thus, the offsite flow north of the site is 17.5 cfs. A 30" storm drain pipe will replace the existing ditch that traverses north to south along Lemay Avenue and convey these offsite flows through the site. Offsite runoff west of the site will collect in Pond A up to an elevation 4982.0. Once at this elevation, the runoff will continue to flow in a southeasterly direction until discharging into the existing drainage swale and into the storm drain inlet at the northwest corner of Lemay Avenue and Rule Drive. Should the ponding water surface elevation in either pond rise greater than the elevations shown in the Detention Pond Informa- tion table the following will occur: Pond A will continue to drain water through the area inlet up to elevation 4982.0. At this point, overflows would follow the ex- isting flow pattern as the offsite flows coming from the west as mentioned above. Pond B, however, runoff will overflow onto the church parking lot to the north at elevation 4980.65 and then drain through the church's release outflow system. The church's release outflow system consists of a 6" PVC pipe and berm located east of their parking lot and west of the drainage swale. Assuming the berm height (4980.64) to be the 100 year ponding water surface eleva- tion for the church site, additional flows would overtop the berm and discharge into the drainage swale. If the ponding water sur- face elevation continued to rise up to 4980.85, overflows would then surcharge onto Lemay Avenue and flow south until reaching the storm drain inlet at the northwest corner of Lemay Avenue and Rule Drive. The downstream drainage conditions at HealthCare International (HCI), south of the proposed site development, have been reviewed as to the impacts of the runoff, from the proposed site development. The HCI storm drainage system has been designed for existing flows of Q100 = 24.2 cfs from runoff flows to the north. The total runoff from the proposed site and to the north add up to be 18.1 cfs. This reduction in runoff can be attributed to the onsite detention as the land develops. When the recommendations from this report are implemented, along with the City of Fort Collins drainage criteria, this site will drain stormwater in a safe and controlled manner. Please call if you may have any questions or concerns. Sincerely, RBD, Inc. AA,, Thomas M. Ochwat Project Engineer C Stan Myers Project Manager cc: 035-110A ttttiFy�i ema a'ti `. V �r O 44 FIGURE 1 \\\ Harmony/Market P.U.D. 1 15.8 OAKRI�GE.DRIVE � ✓ J Existing Swale <990 -' f Evangelical / I / Covenant —�f l Church/ o I r I J Storm Dr'ii r l / I I / l /Temporary Gravel / m / Cul—de—sac Storm C- Type / RULE DRIVE cis cts n Pipe Existing Swale Drain Inlet R w Z. W Q > Q w -I TEM. Oakridge West P.U.D. Engineering Consultants OFFSITE RUNOFF — FiQure 2 • RMINC Engineering Consultants G CLIENT L,_Ul r' JOB NO. 0035-- 1.40 PROJECT Se1P�?brS CALCULATIONS FOR _z6r,0,,z-,e,� MADE BY7Wa_DATE 1. CHECKED BY DATE SHEETOF v� INC Engineering Consultants CLIENT I -JOB NO. 6 3 S 2100 PROJECT Cla�77Yrs CALCULATIONS FOR MADE BY f-AU DATE?- YL CHECKEDBY DATE SHEET 2,OF o2 1� - j -� ^ . �� ` DATE: �� 4-13-90 -- PROJECT: OAKRIDGE WEST 2ND FILING JOB NUMBER: 035-110 DESIGN ENGINEER: SAM BASIN DESIGNATION = BASIN B MASELEASE BATE: 0'2cfo/ac DETERMINE EXISTING Q FOR 2 YEAR STORM ===================================================================== HISTORIC RUNOFF COEFFICIENT .2 BASINSLOPE: 1.5 PERCENT BASIN LENGTH 190 FEET AREA: .739 ACRES HIST TC = 1.87*(1.1—( 1 * ))*SQRROOT 190 ))/ ^ 1/3 = 20.26855 HISTORIC OUTFLOW IS SUPERCEDED BY: .148 .2 1.5 MINUTES CUBIC FEET PER SECOND DETERMINATION OF DETENTION POND VOLUME FOR DEVELOPED CONDITIONS ================================================================== DEVELOPED STORM: 100 DEVELOPED RUNOFF COEFFICIENT CCFAC = .739 .72 = DURATION MIN 5 10 15 30 45 60 90 120 180 360 * .6651001 GROSS VOL. CU. FT. 1819.714 2801.401 3567.597 4932.382 5926.041 6249.28 6752.095 6895.758 7470.404 8332.372 YEAR STORM .72 1.25 OUTFLOW VOL. CU. FT, 44.4 88.8 133.2 266.4 399.6 532.8 799.2 1065.6 1598.4 3196.8 * DETENTION VOL. CU. FT 1775.314 2712.601 3434.397 4665.982 5526.441 5716.48 5952.895 5830.157 5872.004 5135.573 REQUIRED DETENTION -VOLUME IS 5952.895 CU. FT. OR .1366597 ACRE FEET ' DATE: PROJECT: OAKRIDGE WEST 2ND FILING JOB NUMBER: 035-113 DESIGN ENGINEER: SAM] BASIN DESIGNATION = BASIN A 0. RELEASE RATE: 0'2cfa/oc DETERMINE EXISTING Q FOR ===================================================================== 2 YEAR STORM HISTORIC RUNOFF COEFFICIENT .2 BASIN SLOPE: 1.5 PERCENT BASIN LENGTH 220 FEET AREA: .408 ACRES HIST TC = 1 87*(1 ^ ^ — 1 ( 1 * .2 ))*SQRROOT 220 >)/ 1.5 21.81007 MINUTES HISTORIC OUTFLOW IS SUPERCEDED BY: .08 CUBIC FEET PER SECOND DETERMINATION OF ================================================================== DETENTION POND VOLUME FOR DEVELOPED CONDITIONS DEVELOPED STORM: ` 100 YEAR STORM DEVELOPED RUNOFF COEFFICIENT .44 CCFAC = .44 * 1.25 * .408 = .2244 DURATION GROSS VOL. OUTFLOW VOL. DETENTION VOL. MIN CU. FT. CU. FT. CU.^FT 5 613.9584 24 589.9584 10 945.1729 48 897.1729 15 1203.682 72 1131.682 30 1664.15 144 1520.15 45 1999.404 216 1783.404 60 2108.463 288 1820.462 90 2278.109 432 1846.109 120 2326.579 576 1750.579 180 2520.461 864 1656.461 360 2811.283 1728 1083.283 REQUIRED DETENTION VOLUME IS 1846.109 CU. FT. OR 4.238083E-02 ACRE FEET - DATE: 3-3-90 MAX. RELEASE BATE: 0.5cfa/oc PROJECT: OAKRIDGE WEST SECOND FILING JOB NUMBER: 035-110 DESIGN ENGINEER: TMO BASIN DESIGNATION = BASIN A DETERMINE EXISTING Q FOR 2 YEAR STORM ===================================================================== HISTORIC RUNOFF COEFFICIENT .2 BASIN SLOPE: 1.5 PERCENT BASIN LENGTH 220 FEET AREA: .408 ACRES HIST TC = 1.87*(1.1—( 1 * .2 ))*SQRROOT 220 >)/ 1.5 21.81007 MINUTES HISTORIC OUTFLOW IS SUPERCEDED BY: .2 CUBIC FEET PER SECOND DETERMINATION OF DETENTION POND VOLUME FOR DEVELOPED CONDITIONS ================================================================== DEVELOPED STORM: 10) DEVELOPED RUNOFF COEFFICIENT CCFAC = .408 .44 = DURATION MIN 5 10 15 30 45 60 90 120 180 360 * .2244 GROSS VOL. CU. FT. 613.9584 945.1729 1203.682 1664.15 1999.404 2108.463 2278.109 2326,579 2520.461 2911.283 REQUIRED DETENTION VOLUME IS 3.350331E-02 YEAR STORM .44 OUTFLOW VOL. CU. FT. 60 120 180 360 540 ' 720 1080 1440 2160 4320 ' . 1459.404 ACRE FEET * DETENTION VOL. CU, FT 553.9584 825.1729 1023.682 1304.15 1459.404 1388.462 1198.109 886.5794 360.4605 —1508.717 CU. FT. OR ' -- DATE: 3-3-90 PROJECT: OAKRIDGE WEST SECOND FILING JOB NUMBER: 035-110 DESIGN ENGINEER: TMO BASIN DESIGNATION = BASIN B MAX. RELEASE RATE: 0'5cfa/uc DETERMINE EXISTING Q FOR ===================================================================== ' 2 YEAR STORM HISTORIC RUNOFF COEFFICIENT .2 BASIN SLOPE: 1.5 PERCENT BASIN LENGTH 190 FEET AREA: ,739 ACRES HIST TC = 1.87*(1.1—( 1 * .2 ))*SQRROOT 190 ))/ 1.5 20.26855 MINUTES HISTORIC OUTFLOW IS SUPERCEDED BY: .37 CUBIC FEET PER SECOND DETERMINATION OF DETENTION POND VOLUME FOR DEVELOPED CONDITIONS DEVELOPED STORM: 100 YEAR STORM DEVELOPED RUNOFF COEFFICIENT .72 CCFAC = .72 * 1.25 * .739 = .6651001 DURATION GROSS VOL. OUTFLOW VOL. DETENTION VOL. MIN CU. FT. CU. FT, CU. FT 5 1819.714 111 1708.714 10 2801.401 222 2579.401 15 3567.597 333 3234.597 30 4932.382 666 4266.382 45 5926.041 999 4927.041 60 6249128 1332 4917.28 ' 90 6752.095 1998 4754.095 120 6895.758 2664 4231.758 180 7470.404 3996 3474.403 360 8332.372 7992 340.3721 REQUIRED DETENTION VOLUME IS 4927.041 CU. FT. OR .110093 ACRE FEET \ No Text CLIENT �c �/{�JOB NO. 03 J '�.�r 0 INC PROJECT - L 0C_67iCf'2rrs CALCULATIONS FOR Engineering Consultants MADE BVTK_0 DATE 2�CHECKED BY DATE SHEET i OF 3 • CLIENT r � JOB NO. RMINC - PROJECT :k-• TS CALCULATIONS FOR e9e;oeic r Engineering Consultants MADE BY 'f_P'tW DATE I d �CHECKEDBY DATE SHEET - OF 3 CLIENT �2�� JOB NO,TmiD3J ISO INC PROJECT IL1.4647PtS CALCULATIONS FOR Dallela Engineering Consultants MADEBYYXn DATE%AZAICHECKED By- DATE SHEETOF t. TmiDNC Engineering Consultants CLIENT uFw r't' t),ga.p&e bJl=YTa JOBNO. PROJECT S_ ,m ITS CALCULATIONS FOR MADEBY---*"- DATE i CHECKED BY DATE SHEET I OF 7