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Home My WebLink AboutSUPERTOTS AT OAKRIDGE WEST, 2ND FILING - PRELIMINARY & FINAL - 23-87D - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTEngineering Consultants 2900 South College Avenue Fort Collins, Colorado 80525 (303) 226-4955 March 5, 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 Dear Susan, RBD Inc. is pleased to submit this letter and accompaning 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 Basin of South Fort Collins, Colorado, as shown in the vicinty 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 southeas- tern 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 convey 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. Two detention ponds provide for the required storage volume. The ponding area west of the building and the parking lot area will provide the storage volume for Basins A and B, respectively. The Pond Information Table on the Drainage and Grading Plan sum- marizes the storage volume analyses. The outflow release rates were based on 0.5 cfs/ac which produce outflow rates of 0.21 cfs for Pond A and 0.37 cfs for Pond B. These release outflows are then discharged into a 30" storm drain pipe. Offsite flows include the runoff from the basin areas north and west of the site (again, refer to Figure 2). Runoff flows from Other Offices: Vail, Colorado (303) 476-6340 • Colorado Springs, Colorado (719) 598-4107 • Longmont, Colorado (303) 678-9584 the north have been previously calculated in the Harmonv Market P.U.D. Filing One Final report (revised 4/89 by RBD, Inc.) to be 15.8 cfs. The runoff from the church site was calculated to be 1.7 cfs. 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 of- fsite flows through the site. Offsite runoff west of the site will collect in Pond A up to an elevation 4981.8. Once at this elevation, the runoff will continue to flow in a southeasterlv direction until discharging 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 table: Pond A will continue to drain through the area inlet up to eleva- tion 4981.8. At this point, overflows would follow the same flow pattern as the offsite flows coming from the west. Pond B, however, would overflow into the church parking lot to the north at elevation 4980.65 and then drain through the church's release outflow system. If the ponding water surface 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. 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, RB Inc. \1\\1t1111111161IPPPI//!/ QA >Q, Ilk-EGI Thomas M. Ochwat ®�,�.;;Q,� �' �yF,p•;� Project En i eer ;�05 _ 18060T O • =�• eC- Stan Myers,,/'.�, • Project Manager `.'•oY®...�••;,\\` cc:035-110a FIGURE \� Harmony/Market P.U.D. 1 15.8 cis OAKRI�GE DRIVE II jl 1- TO, - Existing Swale f f {9 9°=�� i II / I ( Evangelical / I l Covenant —mot I 9& 8� �J l Church/ Offsite Runoff / I � /Z' I ' 1.7 cis Existing Swale (Pond B I See Harmony/Market P.U.D. 1 Moil Grading and/Drainage Plan-- (o CO v /Pond A l ry /Temporary Gravel / CO / Cul—de—sac c Storm Drain Inlet ---------------- / RULE DRIVE w Z w Q a w J qw, Oakridge West P.U.D. Engineering Cansullanls OFFSITE RUNOFF — Fioure 2 CLIENT pp " JOB NO.R INC PROJECT CALCULATIONS FOR Engineering Consultants MADE BY ! DATE Z b CHECKED BY DATE SHEET Z OF/76 3 Q Iasi <J � a scams/q � x a. -714 AY-, a U SE �� 1 .ADD 7`hG 6G <.,GE 'ea s'. A316 , egG __ 4m ti i i 2 ~A 7.c1&,rS p.Q,FiA�1l.ftt' D3Iz- a.155cis �a u CLIENT ,Tr JOB NO.09S INC PROJECT SNp�Q7brS CALCULATIONSFOR��La9 Engineering Consultants MADE BY77cs DATE 2 CHECKED BY -DATE SHEET OF A�/ ��'� ) RINC Engineering Consultants CLIENT JOB NO. e) PROJECT Cf �P 71�7T CALCULATIONS FOR �e_ �. l- !;f y MADE BY f7GU.- DATE2'IYyiCHECKED BY DATE SHEET 2- OF � • SN,P.vi o _ X Go - S 7 dab �f 2- 7 760 - 517 i J _..! 1 % -Ma 17 7 i T II ,ads . J �La pF — / • 5 `� t' � 1 ' -r- a,— DATE: 3-3-90 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: 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 60 553.9584 10 945.1729 120 825.1729 15 1203.682 180 1023.682 30 1664.15 360 1304.15 45 1999.404 540 1459.404 60 2108.463 720 1388.462 90 2278.109 1080 1198.109 120 2326,579 1440 886.5794 180 2520.461 2160 360.4605 360 2811.283 4320 -1508.717 REQUIRED DETENTION VOLUME IS 1459.404 CU. FT. OR 3.350331E-02 ACRE FEET DATE: 3-3-90 PROJECT: OAKRIDGE WEST SECOND FILING JOB NUMBER: 035-110 DESIGN ENGINEER: TMO BASIN DESIGNATION = BASIN B 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 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, 111 222 333 666 999 1332 1998 2664 3996 7992 * DETENTION VOL. CU. FT 1708.714 2579.401 3234.597 4266.382 4927.041 4917.28 4754.095 4231.758 3474.403 340.3721 REQUIRED DETENTION VOLUME IS 4927.041 CU. FT. OR .1131093 ACRE FEET RINC Engineering Consultants CLIENT G!/C�TT JOB NO. PROJECT CALCULATIONS FOR MADE BY fl-MODATE rLCHECKED BY DATE SHEET OF CLIENT i/ J(��7ff JOB NO. 03 IT- // (3 MOINC PROJECT SGQj0if _`��►U��,1 CALCULATIONS FOR �1G F/C 6M41 �1G Engineering Consultants MADEBV-M-. �[ DATE /_ CHECKED BY DATE SHEET OF 3 m x Y Q-,le-aSr, - assc��,� d.S cys/ate uSi 1) G -rkf- 02 1h z_6 COS or,.>n F;c.. 1 IL El Sb.S z A - 0, 03y5 CLIENT 'G 094e -ry baft p&t t rAl r- a P JOB NO. n IT -B O INC PROJECT CALCULATIONS FOR Engineering Consultants MADE BY- ' DATE CHECKED BY DATE SHEET I OF