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HomeMy WebLinkAboutDrainage Reports - 04/01/1980DRAINAGE STUDY AND REPORT FOR WARREN PARK IN THE CITY OF FORT COLLINS, COLORADO Iii APRIL 1980 TARANTO, STANTON & TAGGE C ONSULTING ENGINEERS FORT CO L L I N S, COL ORADO . I ~ I ------.1 --I I l • ! l ---------- ,, ' ·June 27, 1980 Re: Warren Park Draina&e City of For t Collins ?ar~s and Recreation Department. ~t.5 :fountain Zort Co llins, Colorado 8052l n.';.7}:.: Virgil Taylor :Jear Vi rgil: ~~clo sed with th.is letter are ·copies of the floodway plan and profile t h a t ~il: :-.a.ve to be built along the South and East boundaries of Warren Park. As xr.en - ~ioned in previous correspondence, t he design 100 year storm waters develo?eri fro-... Ha rre .. Shores and North Shores Subdivisions to the West of Warren Par-;._, ant also a small amount from Warren Lake will drain onto your property, re~uir- i.i-.6 fr.i s floodway. From data supplie d by the City of Fort Collins, the fol:ow:..'.._; figures for runoff were used for design purposes: l . A ?eak of 100 c.f.s . to be carried along the South Boundary cie- velo?ed from North Shores and Warren Shores Subdivisions entering at the Southwest corner of Warren Park 2. A peak of 130 c.f.s. to be carried along the East Boundary of Warren Park, running South to North, 100 c.f.s. coming fro~ ite~ (1), 30 c.f.s. from the Warren Lake Spillway and entering Warren Park at the Southeast Corner. :tis pla n ned for a major storm drainage structure to be built under t he in~cr- section o f E. Horsetooth Road and S. Lemay Street sometime in the futur e . 3e- cause it is un~own when this structure will be built, it must be point e~ o~~ t~at should the 100 year flood happen, storm waters would flow over Hors etovt~ ~oad and possibl y damage the road. ~esign inv e rt e l evations have been estab lished by the City of Fort Cv lli~s ~~­ giueering Division for the future storm drain structure. According to }~r~ Z-ngewoen , the outlet invert of this structure on the North side of iiorsetoot~ ~oad will be set at a U,S.G.S. elevation of 5069.00 and tbe inlet inver t whic~ ·..ri:l handle t h e storm water from the floodway and Warren Park will be s et at~ ~.S.G .S. elevation of 5070.00. :-:-,e ultimate design for the floodway through Warren Park calls for a 2 2 " x 36" Corrigated i'..etal Pipe (C.M,P ,) to be built_from the Northeast Corner o f t:-.e ;,ro;,erty at the future storm structure inlet,· _along the East boundary to the 112W.11THAVE. HOLDREGE, NE 61}g4g 6412 S. COL LE G E AVE. FORT CO L LI N S, CO 80525 /'2M\ ??t'\.0557 P.O . BOX 703 HAYDEN, CO 81639 (303)27~ C~ty of Fort Collins Virgil Taylor .... June 27, l9a0 ?age 2 the South, then along the So~th boundary -to the West to connect into the e~istin& 22" :x: 36" c.:1.?. from the North Shores Subdivision. The profile f\)r this pipe is shown as the lowest line on sheet 4 of 5 and 5 of 5, This pipe is <l _esigned to carry approximately 18 c.f.s. at the design slope. This is adequate to handle al: minor storms that may occur. This line will be buried under about a half a foot of soil, just enough to grass. This elevation, or approxitlately 2.333 feet above the pipe invert, will be the flow line for the floodway to carry tte 100 year flood waters. A typical cross section o~ the channels, one to handle ~GO c.f .s., and another to handle 130 c.f.s.~ are ·shown on the sheets. At the deflection points of .the pipe and .channel~ inlet structures will be built to co:lect any nuisance flows that may enter the floodway and also to serve as ffia:..=.- te;:ian ce openings for . periodic cleaning of the sto.rm drain. The flooc.ways have oeen designed to have a minimum of .5 feet of freeboard. The floodway has bee~ designed assuming the entire length and width will be grassed. • I recoull:ilend that this floodway be built as soon as possible to prevent ci ar..a~e taat I.lay occur to the park if a major storm should occur. Because the sto .:w cirain structure under Horsetooth Road is not built at this time, the flooci1-ay should begin 50 feet to the South of the intersection. This will allow sto~ ;,;aters to discharge from the 22" :x 36" C.M.P. and flow over the street: ii .,e:- cessarJ. vfnen the storm drain structure under Horsetooth Road is built, the final 50 feet of C.M.P. and floodway can then be .completed, making this s yste~ fully operational. It is impo rtant to mention that immedia tely West of Warren Park where ~e sh .. ;;::. tie into the e;dsting 22 1.1 x 36" C.M.P. storm drain coming · from North Sh ores is a abandoned ditch which, according ·to the Ci ty of Fort Collins Engineering De?a~t- ~ent, should have been filled in at the time of construction of the Nort h Shores Subdivision; but wasn't. If this ditch is allowed to remain as is, the ne\, fl oo dway will act as a small dam and back up waters within the ditch. This ditcn should be filled in as planned, or a 12" inlet pipe should be provic:ed at the pro?er elevation to drain water from the ditch into the new ::!:11 x 36" C .l1 .?. should a storm occur. This second alternative would cut back sligr.t:y on carrying capacity at the 22" x 36". C.M.P., but that is better than leciYi~_; the ditch ·with no . way to d·rain • the water, perhaps causing an unstable soi.:. con- dition or becoming a breeding area f _or mesquito' s and other nuisance insec ts . If the construction staking or insp e c tion are contracted for separately, ~e ,rnul<l be interes ted in providing on e or both of these services. Ke KOt;l.c a :.s 0 ~e interes ted in designing the storm drain structure under Horsetocth Roac sr,ould the job become available to private engineers. We believe our bac:,;,- 6round with this project and the knowledge our engineers have regarding cirai~- age, structural design and tra~fic problems would give _ you th~ b~st <l~si 6n :for the leas t expense. We hope we hav~ met your needs regarding this project. Ii you have any questions, pleas~ .feel ·. free to ' call me at 226-0557 • l\es;,ectfully submitted, -.: • : & ff, fLLJ . ' •~!\Ober t H. Schemmerling, E,I.T·. T~'"TO, STANTON & TAGGE CO ~S~LTING ENGINEERS \ TARANTO STANTON & TAGGE April 22, 1980 CONSULTING ENGINEERS Re: Warr e n Park Drainage Study Job No. 041-022 City of Fort Collins Parks and Recreation Department 145 East Mountain Avenue Fort Collins, Colorado 80521 Attn: Mr. Virgil Taylor Dear Virgil: In accordance with our contractual agreement, we have completed the drainage study portion of the Warren Park project and hereby submit our final drainage report. This report summarizes the results of our study which was confined to the on site drainage of Warr e n Park. The major problem with drainage at the site cent e rs around the existing 18" CMP culvert near the northeas t corner o f the prop e rty, whi c h was intended to be used as the outlet for the storm water at the Warren Park site. As the report indicates the existing 18" culvert is damaged and is located in a precar ious position with respect to the d e v e lopme nt directly north of Warren Park. We believe that the discharge of the Warren Park storm drainage water, which includes the runoff from developments above the park, should be coordinated with the overall basin design for this area. How e ver, as we discussed at the onset of this project, the o ff site considerations for the storm water from Warren Park is specifically outside the scope of this report. We believe that the off site problems should be researched and we would very much like to provide this s e rvice at your request. During the course of this study, the staff o f the Fort Collins Parks and Recreation Department has given us valuable assistance and we would like to extend our thanks for their cooperation on this report. If you have any questions regarding this r ep ort, or if we can be of further assistance in any way, please do not he si tat e to contact our office. 112W.11TH AVE. HOLDREGE, NE 68949 (308) 995-6677 6412 S. COLLEGE AVE. FORT COLLINS, CO 80525 (303) 226-0557 P.O . BOX 703 HAYDEN, CO 81639 (303) 276-3834 City of Fort Collins Parks and Recreation Department April 22, 1980 · Page 2 Very truly yours, ~~8 Donald N. Taranto, P.E. TARANTO, STANTON & TAGGE CONSULTING ENGINEERS DNT:cs Enclosure. DRAINAGE REPORT FOR WARREN PARK FORT COLLINS, COLORADO I. It is the intent of this report to show the quantity of runoff to be developed from this project. The area will be a public park to be used for the enjoyment of all Fort Collins residents. Proposed construction within the park shall include tennis courts, sports field, rest rooms, sprinkler pumping house, picnic facilities and a playground. It is important that the runoff is quickly disposed of. Therefore, items to be covered in this report are as follows: 1. The location and area of the project 2. Effects of outside areas 3. Design criteria 4. Runoff estimates and drainage ways 5. Conclusions and recommendations 6. Design calculations II. The location and area of the project. The Warren Park development consists of 26.97 acres in the NW 1/4, NW 1/4 of Section 31, T7N, R68W in the Sixth Principal Meridian, Larimer County, State of Colorado, lying immediately South and East of the NW corner of said Section 9. III. Effect of Outside Area As can be seen on the Fort Collins, Colorado U.S.G.S. QUAD Map (Exhibit A), the ground of this project falls from West to East, "o C ·./ I I . Lake 4991 • 49t EXHIBIT A Ii • TAIIANTO r~:u: Normally, drainage would enter the park from the West, but the subdivision which bounds Warren Park to the West, North Shore P.U.D., has been fully developed in terms of drainage and runoff from that project is collected by a storm drain system which discharges on the park's South property line into an open ditch and to the North onto Horsetooth Road. Consequently no drainage from other areas flows directly over this project. Indirectly the drainage ditch along the South boundary will be on Park property and will carry a major portion of the said subdivisons's storm water runoff. IV. Design Criteria The design criteria for this report was based upon the guidelines and recommendations set forth by the "City of Fort Collins Drainage Requirements and Design Specification" manual. The "Rational Method" was used to determine runoff flows from the site for a two year and a hundred year storm for both historical and dev~lop~d flows. Since the development of Warren Park will not significantly increase the storm water runoff, the ground condition factor will remain constant for both historical and developed conditions. Therefore, the respective runoff quantities for the developed and undeveloped conditions are equal. The "Rational Method" relates runoff to rainfall intensity by the following formula: Where; Q = Maximum peak rate of runoff in cubic feet per second for a given design storm r l C = Unitless adjustment factor based on the given design storm f C = Unitless runoff coefficient based on ground vegitation and permeability of the soil .. i = Average rainfall intensity in inches per hour for a duration equal to the time of concentration. The time of concentration is the time required for water to flow from the most remote point of the project to the point of discharge. Both of the factors Cf and C drainage manual. Cf for the the 100 year storm as 1.25. conditions. were taken from tables provided by the two year storm was taken as 1.0 and for The factor C was taken as .3 for all The "Time of Concentration'' was found by the following formula taken from the Fort Collins Draina 9:! Manual: where Tc= 1.87 (1.1 -cfc) o 112 S 1/3 Tc; Time of Concentration in minutes Cf and C = factors given by Rational Method Equation D; Longest distance traveled by runoff from the upper end of watershed to the point of discharge in feet. S = Average slope of the watershed in percent. The distance D was taken to be 1600 feet and the average slope of the ground is 0.8 percent. Rainfall intensities were based on the time-intensity curves provided by the "Fort Collins Drainage Manual'' and shown on Exhibit B. V. Runoff Estimates and Drainage Ways. Because .of the gently sloping ground from West to East, the flow will be allowed to drain overland. No special swales or drainage structures are needed for this project. The 2 year storm is estimated to produce 7.12 cubic feet per second and the 100 year storm is estimated to produce 26.60 cubic feet per second. All the runoff will be discharged from the project at the Northeast property corner . VI. Conclusions and Recommendations Care must be taken when grading this property. It is very flat and all grading should be checked to prevent oc c urance of low spots which could pond water. No on-site retention is needed since there is no increase in discharge due to development. There is a low point at the Southeast corner of the park parking lot at which a storm drain inlet needs to be constructed. This inlet should be a single inlet catch basin as shown on Exhibit C. The storm drain from this catch basin shall be 12 inch I.D . C.M.P at 1% grade to the existing drainage swale on the south boundary line. Based on this report the following recommendations are made: 1 . There is at this time no way to adequately remove the discharge from the Northeast corner after it leave s the property. The only drainage available is a damaged 18 inch C.M.P. We believe this a: ::, i t en w :J: 0 z I 4 3 ► 2 ~ -en z w ~ z 1 2 Year 0 • CITY OF FORT COLLINS, .COLORADO RAINFALL INTENSIJY_D _URA:TJO~ __ CURYE Based....on-»ata ...and _Procedures _'From _NOAA ...Atlas 2 Percipitation -Frequency Atlas of the Western U.niJe1i-5J.ate__sJ1>l._llI _·_Colorado '-100 Year 80 120 TIME IN . MINUTES EXHIBIT :B 150 180 NOV. 1175 NOTE: All opplicob/8 noftJs and dtJto1ts on Owg. S-34-/3.lo also apply lo this stondord d#tJil. Asphalt or Concrete Surfacing 13 Inlet toil. S-34-13.2a) Cement Grout or Mortar --------__ _ ~a-v• ,:.: e.Oo --=:, 0&> ·o .-,m....:::.(f!~,.,.,.....,!t... o,4:> c:: "'""' _··~·--·· ..... ----------4011 -----------........ 0 Floor slope may be p~ monolithic with base. SECTION THRU LENGTH c;:::_:r_Concrete Surfoci11 Cem ent <i r c,111 M o rfnr e, " 0 c:~~. . Base Course :.~.::, -1-~-i,-.:.;-- Backfill around structure to be hand tamped in 6" t---~ lifts ( Backfill method 0 8 °) Undisturbed ground or firm foundation material------SECTION THRU WIDTH EXHIBIT C Out ,1 1 pipe in ~•de or end wal I. (to be set flush with 11'· ,; e wol I' of structure) Pipe Beddin9 1 • ,-__/ A 8 B PLAN SECTION A-A ·1 A A~ a 1· 1 l&lll" 1" I -~r. -8 I ~ I[ L Ill I ltI r , I I I· CORNEAS RELIEVED TO ~R(VENT RO CKINI id 191 i1i Iii .. st 1/4" A.....J PLAN . • ;::- ... . , I II ■ I I J ·I SECTION B-B NOTES : I. Costing Specdicotions · A STM A· 48, with o minimum tensile strength of. 25 ksi (Closs 25) 2 . All costings t o be dipped in asp/la/I base poin t . 3 . Minimum Grate Opemnq Area : 330 SQ. ill. . I EXHIBIT C • problem should be looked into to avotd major drainage problems in the future. 2. Drainage from Horsetooth Road above this area has a tendancy to accumulate in a low spot just East of the entrance road and we believe a remedy is needed, 3. It is recommended that a new drainage system be constructed East along the South property line and then North along the East property line to provide proper drainage of storm waters generated by the upper developed areas . There is enough grade to allow construction of either a swale or a storm drain. Thts storm drainage system should be sized to handle the 100 year developed flow from all upper areas and from the overflow spillway of Warren Lake. This recommendation is strictly for the drainage waters of outside areas and is therefore not a part of this project. VII. Design Calculations The following pages show all design calculations. • City of Fort Collins Job No. 041-024 ~arren Park Drainage Study DESIGN CALCULATIONS WARREN PARK Sec. 31, T7N, R68W Assumption: Because of the limited development, we will let the developed drainage be the same as the undeveloped drainage. Method: Rational Q = Discharge, Cf = Correction factor, C = ground permeability A= Drainage Area in Acres Determine Drainage for a) 2 year nuisance flow b) 100 year (Major Drainage} From Fort Collins Drainage Manual C parks= .25 Let C = .3 overall condition C playgrounds= .35 Also Cf 2 -10 year storm= 1.0 Cf 50 -100 year storm = 1 .25 AREA OF PROJECT = 26.97 ACRES 27 ACRES TIME OF CONCENTRATION From Fort Collins Manual For 2 year flood D = length of watershed S = Slope in% (avg.) D = 1600 ft. S = .8% Avg. T = 1.87 (l.1 -(.3) (1.0)) 16001/2 = 64.46 minutes C -------------_81/3 From rainfall-intensity curve, Drainage Manual Tc= 64.46 minutes i = .88 in/hr • Q = (1.0) (.3) (.88) (26.97) = 7 .12 c.f.s. For 100 year flood Tc = 1.87 (1.1 -(.3) (1.25)) 1600 112 = 58.34 minutes .81/3 From rainfall-intensity curve Tc= 58.34 minutes, i = 2.63 in/hr. Q = (1.25) (.3) (2.63) (26.97) = 26.60 c.f.s.