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HomeMy WebLinkAboutTIMAN PUD MASTER PLAN - 26-88B - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTi 9001INC Engineering Consultants 2900 South College Avenue Fort Collins, Colorado 80525 303/226-4955 April 4, 1988 Susan Hayes City of Fort Collins Storm Drainage Department P.O. Box 580 Fort Collins, Colorado 80522 RE: TIMAN P.U.D. MASTER DRAINAGE REPORT Dear Susan: Site Location On behalf of Jeff Timan, RBD Inc. submits the following Prelimi- nary Master Drainage Report for the Timan P.U.D. The Timan P.U.D. site is located along the west side of State Highway 287 (South College Avenue) north of Trilby Road. The 56 acre parcel is bounded on the north by Skyway Drive, on the east by State Highway 287 on the south by Trilby Road and on the west by the First Freewill Baptist Church, Skyway Acres Subdivision and the Foothills Gateway facility. More precisely this location can be described as being situated in the east half of the southeast quarter of Section 11, Township 6 North, Range 69 West of the 6th P.M. in Larimer County, Colorado. Existing Drainage The site currently contains a commercial parcel in its southeast corner and one residence. The vast majority of the site is used for pasture. The site is traversed by a small irrigation lateral which enters the site in the southwest corner, and exits the site in the northwest corner. The lateral meanders along a ridgeline through the site. The site slopes generally eastward at slopes of 1.5% to 8% below the ridgeline and approximately 2.5% above the ridgeline. Two board ridges protrude eastward from the prin- cipal ridge. These board ridges have the effect of dividing the lower area into three basins. Each of these basins have low areas which are formed by the state highway embankment. These areas are drained by culverts which run under State Highway 287 Other Offices: Vail, Colorado 3031476-6340 • Colorado Springs, Colorado 303/574-3504 and the commercial two northern basins lying areas. Offsite Drainage areas on the other side of the highway. The appear to have limited wetlands in their low Offsite drainage flows have a definite impact on this site. Of- fsite flows will impact the site along the west property line. No offsite flows are anticipated from any other region. The first and most southern offsite area contributing flows along the west property line is largely undeveloped area occupied by a single church building with an unimproved parking area (see Of- fsite Exhibit A in Appendix). Flows from this 7.6 acre area are currently diverted into the forementioned irrigation lateral. This lateral appears to have adequate capacity to handle 100 year flows from this area, without substantially impacting the Timan P.U.D. The second offsite area is comprised of portions of the Skyway Acres residential area and the Good Samaritan Center. Drainage flows are collected in the street system in this area and flow undetained into a concrete lined swale that runs northward just west of the west property line of the Timan P.U.D. This swale appears to be greatly undersized for 10 year as well as 100 year flows. Therefore the majority of these flow will enter the site undetained along the described swale. The third offsite area is comprised principally of the Foothills Gateway facility. Drainage from this area flows eastward until it is intercepted by a grass swale which is a continuation of the concrete swale mentioned in Offsite Area 2. This grass swale has greater capacity due to a more substantial berm along its eastern sideslope. This swale carries flows northward to the storage pond which lies just west of the northwest corner of the Timan P.U.D. At this point flows either enter the storage pond or fol- low the Foothills Gateway entrance road and flow into Skyway Drive. As a result of these conditions no offsite flows are an- ticipated from this area. Proposed Drainage The attached Master Drainage and Utility Plan illustrates the ap- proach taken in facilitating drainage onsite. Onsite drainage will be handled rather simply utilizing the two northern low areas for the required site detention. This will be done in or- der to reduce or eliminate grading in the wetland areas. An ad- ditional improvement will be the piping of the irrigation lateral from a point close to where the lateral crosses the west property line to the north property line. This will simplify site grading and access to the area above the lateral. Basin A comprises roughly the northern third of the site. Drainage flows in this area will be conveyed through a system of curb and gutter, culverts, swales and storm drain piping to the forementioned low area. This area provides the required deten- tion with a minimal amount of grading. Most of this grading will be above the wetlands thus reducing its impact. The culvert opening will be redesigned to restrict outfall to the required rate. No offsite flows will enter this basin. Basin B comprising the remainder of the site will be handled in much the same manner. Drainage flows will be conveyed in a similar system to the low area at the midpoint of the highway frontage. Again grading will be limited in the low area to areas above the wetlands. The principal difference from Basin A, will be that facilities carrying flows from the area adjacent to Of- fsite Area 2 will be oversized to accommodate the undetained of- fsite flows. (;nnrinci nn Calculations which substantiate the proposed approach appear in the attached Appendix. All calculation reflect use of the City of Fort Collins Storm Drainage Criteria. Detailed calculations for the sizing of culverts and the design of outlet works will be submitted with the Final Master Drainage Report. The approach outlined in this report should provide for the efficient and safe conveyance of drainage through the site. Sincerely, RBD, Inc. Stan A. Myers, P.E. cc: 272-001 • • APPENDTX OFFSITE DR EXHIBI _ I ! •� '' GOO®: 1... ; .AMA IT'A I' I x II �.T R I � �,, •� 'b J l AY; AC D VISI6N f , QFFSIT XR JAi�_ 1 �, - �;� 01, &� C -ft DRAIN P N - 36.85cf 10 Q 100 = 55.5 c AINAGE r A S, OTHILL GATE�WM. SCALE: 1'=200' Ar 09 6/ A40 NO x Cf S, ..141 _41i 10 GRASS. SWA 22.3, A s Ifs �INC rnnctiltnntv u DATE: _;/23/88 PROJECT: TIMAN JOB NUMBER: DESIGN ENGINEER: 0� i 1 SAM BASIN DESIGNATION == A% • DETERMINE EXISTING 0 FOR 2 YEAR STORM HISTORIC RUNOFF COEFFICIENT BASIN SLOPE: 4.2 BASIN LENGTH 1200 AREA: 20.09 ACRES HIST TC = 1.87*(1.1-( 1 )) *SQRROOT 120o HISTORIC RAINFALL INTENSITY: HISTORIC OUTFALL: 7.055368 .25 PERCENT FEET * .25 )) / 4.2 34.14359 MINUTES 1.404752 INCHES/HOUR CUBIC FEET PER SECOND DETERMINATION OF DETENTION POND VOLUME FOR DEVELOPED CONDITIONS DEVELOPED STORM: loO DEVELOPED RUNOFF COEFFICIENT CCFAC 20.09 . 8:'.5 DURATION 111 N 5 J 10 15 0 45 60 90 120 18 () 360 21.34563 GROSS VOL. CU. FT. 54966.24 84619. 08 107762.8 148987.4 179001.9 138765.6 203953.7 208293.1 225650.9 251687. YEAR STORM .85 1.25 OUTFLOW VOL. CU. FT. 2116.61 4233.221 6349. 831 12699.66 19049. 49 25099.32 38098. 99 50798.65 76197.97 152395.9 yF DETENTION VOL. CU. FT 52849.64 80385.86 101412.9 136287.8 159952.4 16_066.3 165854.7 157494.E 149452.9 99291.58 REQUIRED DETENTION VOLUME IS 165854.7 CU. FT. OR 0.8075 ACRE FEET RINC CLIENT /�A/1�J _SOB NO. a7J-2 'CYC PROJECT ._ Z [.�./ANS CALCULATIONS FOR-Z)Ejg ?J 4_ Engineering Consultants MADE BY` Ili DATE*? CHECKED BY DATE SHEET OF PARLL ,G A 1/C�L i IkY_ B5.4 p ►813 i8r9 - Qp Ae. FT I + a3 sG 3 538 = 0. 5a A e 0500 1. 7 5.Ae Per . Gam/ ,� vL zi rv,q b U r J G. {AEG ioF BA.S w '4 l 547�0 8� 132 � 1.84 f 5_� 3 - 41 s�0 121 4*3.'� 14 788 sl 3.8ZA0 FT- Soo:c t... _.__.__.... i i EVEA,�;OAt- (2-^O; IJ(el r l _... _ 5T l i Zoo L I it ' » _ _. .. .... ; . I i DATE: 3/28/88 PROJECT: TIMAN JOB NUMBER: 272-001 DESIGN ENGINEER: SAM BASIN DESIGNATION = 10 13 DETERMINE EXISTING Q FOR 2 YEAR STORM HISTORIC RUNOFF COEFFICIENT .25 BASIN SLOPE: 2.4 PERCENT BASIN LENGTH 1850 FEET AREA: 39.3 ACRES HIST TC = 1.87*(1.1-( 1 * .25 ))*SQRROOT 1850 ))/ 2.4 1/3 = 51.07826 MINUTES HISTORIC RAINFALL INTENSITY: 1.126278 INCHES/HOUR HISTORIC OUTFALL: 11.06569 CUBIC FEET PER SECOND DETERMINATION OF DETENTION ------------------------------------------------------------------ ------------------------------------------------------------------ POND VOLUME FOR DEVELOPED CONDITIONS DEVELOPED STORM: 100 YEAR STORM DEVELOPED RUNOFF COEFFICIENT .85 CCFAC = .85 * 1.25 * 39.3 = 41.75625 DURATION GROSS VOL. OUTFLOW VOL. DETENTION VOL. MIN CU. FT. CU. FT. CU. FT 5 107524.8 3319.706 104205.1 10 165531.6 6639.411 158892.2 15 210805.2 9959.116 200846.1 30 291448.8 19918.23 271530.6 45 350163 29877.35 320285.7 60 369262.8 39836.47 329426.3 90 398973.6 59754.7 339218.9 120 407462.4 79672.93 327789.5 180 441417.6 119509.4 321908.2 360 492350.4 239018.8 253331.6 REQUIRED DETENTION VOLUME IS 339218.9 CU. FT. OR 7.787395 ACRE FEET Mf%INC Engineering Consultants • CLIENT -7-/ PROJECT �I A �T_�l_��L+PIJ%�al'-� CALCULATIONS FOR MADE BYSA IL" DATE CHECKED BY DATE JOBNO. SHEET OF le (kh I/ _A?_A?6A Vc VO/ 1;5- 21870 .'Z /78,0 = o. S AC. F T 50o b �43�C> ��� 38a8r0 �.25 /32000 23008b $.2ib - /asooa 41508o J,53 E.CeV A Vol- I PAD a 7E'lJ o, S AC-1=7 &%300 lO'ZOSO 151000 2e.0oSo S,97 Z<:X>4 88000 5 ,2 02 nc> C� 0z 01 04 c oco ,I • M Wt:INC Engineering Consultants AeE/A _ 7 Ae. 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