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HomeMy WebLinkAboutDrainage Reports - 06/27/1989FORT Com.:% y 07111,121M FINAL DRAINAGE REPORT FOR THE WOODLANDS, FILING FIVE PREPARED BY, STEWART & ASSOCIATES, INC. JUNE 27, 1989 STEWART&ASSOCWES Consulting Engineers and Surveyors June 27, 1989 Mrs. Susan Hayes Storm Drainage...Utility City of Fort Collins P.O. Box 580 Fort Collins, Colorado 80522 Dear Susan: The Woodlands, Filing 5, is a proposed single family residential subdivision situate in the Southwest.I of Section 35, Township 7 North, Range 69 West of the 6th P.M. It is bounded on the South by Harmony Road, on the West by Starflower Drive, on the North by Marigold Lane and a part of The Woodlands P.U.D., Filing 3, and on the East by Larkborough Subdivision. It is located in the Mail Creek Drainage Basin and contains 17.3899 acres, gross. The Westerly two—thirds of the site slopes gently from Northwest to Southeast, and the Easterly one—third slopes more steeply from North to South. The site presently has a ground cover of native grasses and weeds. There are some existing small volunteer trees and tree stumps located on the property. There is an existing regional drain channel along the north side of Harmony Road which runs west to east along the entire length of the site. The original plan for this drain channel was prepared by Cornell in 1980. The plan for the channel shows four concrete drop structures being constructed along the channel to cut the slope from 1.2 percent to 0.4 percent. We have inspected the existing channel and found that the drop structures were not constructed. The existing channel has very little erosion, and there is a good growth of grass in the bottom and along the banks for most of the channel's length. The maximum flow in the channel, according to the preliminary report by EDAW, is 74 c.f.s. The channel has not been subjected to this maximum flow, but our calculations, shown on sheet 7 of this report, show that the maximum velocity will be less than 5 feet per second. Both the City of Fort Collins Storm Drainage Criteria and the DRCOG Urban Storm Drainage Maunual say that flow velocities of 5 f.p.s. and under are permissible in channels having vegetation and soil type such as in this channel. The existing channel must be cleaned of debris and some young tree sprouts should be removed, but other than that, it will be best to leave the existing bottom.and side slopes intact as much as possible. The existing channel has been surveyed and cross — sectioned to provide information for this report, and the final channel shape and slope shall be surveyed and certified to after construction is completed. - The outlet for this drainage channel is an existing 42 inch RCP under Harmony Road. This 42 inch pipe which has flared end sections, empties into the Mail Creek Channel on the south side of Harmony Road. This channel system will be maintained by the City after a minumum 2 year maintenance period by the developer and after City acceptance. James H. Stewart 1 and Associates, Inc. 214 N. Howes Street P.O. Box 429 Ft. Collins, CO 80522 3031482-9331 Mrs. Susan Hayes June 27, 1989 Page 2 Tract "A" also contains an existing storm water detention pond that was designed by Cornell Consulting Company on The Woodlands, Filing 3, Utility Plans dated August 11, 1980. The pond is shown on Sheet 11 of 13 Sheets. It was designed to have a capacity of 4.16 acre feet and provides detention for Woodlands, Filings 1 and 3. The pond has been rough graded and a 24—inch R.C.P. outlet pipe has been constructed. It has a 9-3/4" opening"in the existing restriction plate. We plan to enlarge this pond so that it will have a volume of 7.08 acre feet. The 9 3/4 inch diameter outlet plate allows an outflow of 6.1 c.f.s. with a pond depth of 6 feet. Although the original outflow was to be 10.0 c.f.s., we plan to leave the existing restriction plate in place to offset the undetained release from approxomately 5.3 acres of rear yards along the regional drainage channel. The net increase in detention pond volume is calculated as follows. Additional volume gained by increasing pond from 4.16 acre feet to 7.08 acre feet equals 2.92 feet acre feet. Loss in volume caused by decreasing the outflow from 10 c.f.s. to 6.1 c.f.s. equals (10) (10800) — (6.1) (10800) = 42120 c.f. = 0.97 acre feet. This results in a net increase in volume of 2.92 — 0.97 = 1.95 acre feet. There is a cattail area in the existing detention pond which we propose to retain as a wetland. The. 42—inch inlet pipe that discharges the Filings 1 and 3 runoff from Marigold Lane will be extended during the construction of Filing 5. An 18—inch pipe will be constructed from the inlet in the East end of Woodlands Way to the detention pond. The runoff from the North half of Harmony Road between Starflower and the Southeast corner of The Woodlands, Filing 5. will flow in the proposed curb and gutter to an existing curb inlet in the Larkborough Subdivision approximately 135 feet East of the said Southeast corner. An existing 24—inch C.M.P. carries the runoff under Harmony Road to the Mail Creek Channel. The street flows within the Woodlands Filing 5 are less than the Maximum allowed. The minor flows will not overlap the curb, and the major storm flows are far below the allowable. Sizing calculations for the two new inlets are shown on sheet 8 of 10 in this report. The drainage calculations, drainage table and drainage plan are included as a part of this report. Sincerely, Phi l l i p I. Robbii nssonn,, P.E. & L.S. Vice President Ikm enclosures o•°�Q I. ROBM'O' e. R • r i • \' r 2 n F, Cj%%. COMPUTATIONS STEWART&OLS, -)CIATES Consulting En3ineers arKi Surveyors 214 N. Howes St... Ft. Collins, CO 80521 (303) 482-9331 By: FIR Date -YILOJ69! Client: Gr i u) fcik-7o :�S;' Fa1)?er- Sheet No. 3 of /0 T-7— Chkd By: Date Project: Subject rvss C4 6 C' Li 0+ bod Apds Filh, C 19 lo reS 0-5 PE 1 OU44)OkI -7-71 De i e irN 0;r? 4- FOR TNF- E F-! -�I+F- E -7 6 U 4" 4 A /f:� 5�; lom:i c7F,-rF-wrio" Cl->,LCULATIW) �, 90 '2. Z: 9 4cl Y Tor S CC I; -z- U Z. Z 7! 4a C- This' 441 Oki 1 6 0 oJ- FO �z e er? 6' 1- (f f S 1-41r, rq c:;, cl T-11 x/ 51 [epor4- Fvr vjoo, Ir In 0 5� EpAt%/, f0�cxl de-�errW n volvAe J> O;'n V/ 01 L�> e. 6V n CL -V d a 0! nd ofIOCG��d in -r-!' 8 Q r�n' tt R one jo7el 6e 1 e 7� dk: e- v'/ 6 -P, FAQ Pe e U!r i r G� 1, lei O�pio 0 or" I t4 -e wq S to is C e `be /0.6 13 v-� 4- 0. rq et 4 r-11 lee4 - . y3j� 1) (� �0 .0 1 el 0 413e fkn-A t-\ t r-' c 0 dit F1 p + The r ue, cuflef lu5 1 C far-J.e e, 0 f�.ee- -h-,c /I e; uk) 1 - I , I -e - 1-47 V-0 �) rq 1 1 Z3'c( rjpk' is o- i r-1 cz 's )io5 0^-1 -:5, to i-rx t-url e & n' i 6ke- ble r- 0P C)s e� C vve v �2 4-i f- I- -I- 7771ep: 0. 4, :1 a../ re r U I F-el. 0%- Ae, 0 n on olu/'-Xe 'o-(- -7,0: do14,-+bLe'-Fu '7,013 i's �de5? vc4c - COMPUTATIONS STEWART&A& CIATESQ Ccmisullin3Erp .3ineersard Surveyors 214 N. Howes St. . Ft. Collins, CO 80521 (303) 482-9331 By: Date Client: 67i yh,ct r-) Q A— EaAet- Sheet No. 4—of 10 Chkd By: Date— Project% V0Q(J dS 11`7 CI Subject De4e n-�-) 0,1 e-!5! U irervlen-�J. I- T- 10 7:3i 3 6 -to 44 100 1.01 100006 5-01600 5� 1 19 -517 3 3 30.7 1 10,vc 1. T It I f— 6 6 7 113 3:�-1 117. 11 I I t to Ito 3 60 D:e4-'- vl�-N Oil\ COMPUTATIONS. STEWART&AS; CIATES CcRisulting En3ineers and Surveyors 214 N. Howes St. Ft. Collins, CO 80521 (303) 482-9331 BY: Date Client: G-tj i 0, in 0 5 Fcali4 er'—Sheet No. of Chkd By: Date— Project: �. &O'dlczn JJ Subject F1 m 1L" 3to-(I :0 Wrl Th e ex is:4n J !1 Vm 0� 0! r\ U, 0' Vme -7. P os-e')- /::;�Iio di 04 IC I CV 7- 61 e' L/ /4.3 )7 1 Z-03 9 70 -7 4- -57 3 1-1 .. ........ oT L+- \3 C U) m D- Vqv) replo�--- 4-hr(IY5 ice (J r e: 'r-(f -,F4' -.,re -�e vt/ill !,be: Cz J 1A- COMPUTATIONS STEWART&ASS - TES Consulting Engineers and Surveyors - 214 N. Howes St. Ft. Collins, CO 80521 (303) 482-9331 BY: FIR Date Client: 6io)farla k Et-,Aet- Sheet No. 6 of 10 Chkd By: --. Date Project:— w/00 0(/CZ n JS- F—)//.,17 Subject '(fc?)CC))G'i 1'Qe) 0-� run-04 fron Ucu'f?�f 6'jeveto ed� 7 TL pf V I.U 44 - 0 (1 6)"�c. all /ic)7- Tc IV S., z -71 T, 0 ip c� Fic /;4 c( 7o 130 -t e T V07 (I I �rj I z -F, z t L 7 too, -Z 1 5 - L> Apt c -1cij L3 1 0'.2 e: :5 I + �1450� I. 7 1.11 LS 3 rPIS Z Z. L Min 100 19 m 1) I � ! It , � 1 I I � I i � !- ' i ; i 1 7 7 5.7.311 1 3i?- p c J it 5 3JI -70 fit I 6i.- 5- 1 j4-:� 0 e ir E 2. 0: 0�c (�q U T- .07 6 t 2- Z4-- n V ou 4- T<— '(,v t of'; m; flu{ 0 2to, 5)1( c-TJ 0" el'N�S'3)(1 Z.10) q)po <:� oq-- 71, L3A 51 l T6 'F Q�I- .�f1 i 1 .3 5)1 rGG J-J! b 2 .,.I 1-1. COMPUTATIONS STEWART&AE )GATES Consultirig En3ineers arxi Surveyors 214 N. Howes St. , Ft. Collins, C080521 (303)482-9331 By: PIK Date Client: 6)'U) ic;t f)Q '4,- -F-c2 +;i r- r- Sheet No. 7 Of Chkd By: Date- Project: bf- WQQdlands F i 'I t? 9-4 57 V I Subject -EE�qiQnal I 4-1 OT r-�L C f7&n^e) - Qm re r ading be. Ye 14v 4- don' e rV r- 5 yPerv(si'pn o-P r4-c)rl 7 ell. 0. 17.3 10. 0) Z5 /V1 a S< I m U^k 1COL-/ r-4 iC:Oh✓��i%-j er 55 44 /A/p 610 --t 2: C). I lk -z 4-�, i V s 1/ 4�. ) !e, !7, -J -4 6.771 . 14-r T- 1(0 7e. Th es e 41 C- Cult, brir. r -5-!A U e 11 0<- tj 4!Loe i L-�/ J�7 Deli n �Ir a4 101 k% rbonl r4- 611(n. 4-or/,..\ p rci i /I C �-ko /116t n ct)) r,% c�5 V I a, re- I'ssiblLC LA G54- I 0� �r LY rs 4 lUL-V' 0 r V J COMPUTATIONS STEWART&AS )GATES Consulting En3ineers arKi Surveyors - 214 N. Howes St.. Ft. Collins, CO 80521 (303) 482-9331 By: Date Client- C�flj)(-Ona &: Fc'/-4ef- Sheet No. 8of Chkd By: Date -Project: kJ00C4_1(21r_W4jS F0110� Subject 411e ro kv% Lo re V T\).o Jm in! Ic o� 4 de W&d1Ckrk_tY 5-= 2-4,& cLc, 64� o'� is- f�jc 14A Orts C, 14. 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