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Home My WebLink AboutLINDENMEIER ESTATES PUD - PRELIMINARY - 24-94 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTSTEWART&ASSOCIATES 10 S. M LDiRUM,FAX as2-9g OLLINS, CO 80521 Consulting Engineers and Surveyors By: Date: Client: ?�- • C2�j Sheet No. ( of Project: L I D�->>�t�1ICI Subject: ii ZE-EU VA t 0 tit?y "Llll 11Cc o� i Z; Z, j ZCoO/ Co l0 1Jo2j� 1 N�'c S 1,37 L t Z�, 2 O Ol3vo �Ew.w� -T ►.ka r 71 . i 1;AS1� -1wAT ColoiQoc- i �—�'eJoa,,►a Zr�,�e,� `�e��as 2',3 i j iJ i 1 i � i I SUSBASIN:..T.O.C.:..,..:(.100yt)... ........... D. Pnt Slope c Cf Length (feet) OverLTc (min.) Vel.Chan (ft/sec.) Tc Chan. (min.) Tc Tom] (min.) COMMENTS L 1 2.00 1.00 50.00 1.0 Tc (100) 1.00 300.00 225 2.2 ......3.31 LNGST. ERL.+CHANNEL 0.90 = Runoff C 1.00 = Cf 2,10 1.25 =Cf 100 D. Pnt Area (acres) C Cf I (2yr.) (in/hr) I (10yr.) (in/br) I (100yr.) (in/hr) Basin Q (cfs) Comb. Q (cfs) COMMENTS 0.23 1.00 3.30 0.76 0.81 2 yr. runoff 1.00 5.65 1.30 4 10 r. runoff �jj 0 1.00 7.00 1.61 _j I 100 yr. runoff 0.90 C 1.00 =Cf(zlo) 1.25 =Cf 100 .SUBBASIN..., OC.:.. 000YO-...... D. Pnt Slope (0/0) c Cf- Length V (feet) Overl-Tc (min.) Vel.Chan (ft/sec. Tc Chan. min. Tc Total min.) COMMENTS 2.001 1.001 50.001 1.01 1 Tc (100) 1.001 1 300.001 1 2-251 2.2 1 .... .,.:a3j LNGST. OVERL+CFIANNEL 0.90 = Runoff C 1.00 = Cf 2,10 1.25 =Cf 100 D. Pnt Area (acres) C Cf I (2yr.) (in/br) I (10yr.) (in/br) I (100yr.) (in/hr) Basin Q (cfs) Comb. Q (cfs) COMMENTS 0.75 1.00 3.30 2.48 25 2 yr. runoff 1.00 5.65 4.24 42 10 r. runoff 1.00 7.00 5.25 100 r. runoff y 0.90 = C 1.00 =Cf(zlo) 1.25 =Cf(100) ...... .... �).. SUBBASIN O.C. Alfflyr X D. Pnt Slope c Cf Length (feet) Overl-Tc (min.) Vel.Chan (ft/sec.) Tc Chan. (min.) Tc Tom] (min.) COMMENTS' 1.001 0.56 110.00 10.5 Tc (100) 1.001 400,06- 0.70 9.5 20 1 LNGST. OVERL+CHANNEL 0.45 = Runoff C 1.00 = Cf 2,10 1.25 =Cf 100 D. Pnt Area (acres) c Cf I (2yr.) (in/hr) I (10yr.) Cin/hr) I (100yr.) (in/hr) Basin Q cfs Comb. Q (cfs) COMMENTS 0.77 0.45 2-35 2.23 22 2 yr. runoff 0.45 4.10 3.89 "',,-:3 9 10 r. runoff 0.56 6.60 7.83 .8 100 yr. runoff 0.45 = C -1.90 =Cf (zlo) 1.25 =Cf 100 3,�;-:j I. fb = ArBataC) mis page D. Pnt. Area (acres) C Cf I (2yr.) (in/hr) I (10yr.) (in/hr) I (100yr.) (in/hr) Basin Q (cfs Comb. Q (cfs) COMMENTS 4 1.17 0.45 2.35 1 242 -.2 yr. runoff 0.45 4.10 2-161 22 10 yr. runoff 0.56 6.60 4.341 100 yr. runoff 0.45 = C 1.00 =Cf 2,10 1.25 =Cf(100) D. Pnt. Slope C Cf Length (feet) Overl-Tc I (min. Vel.Chan fUsec. Tc Chan. min. Tc Total min.) COMMENTS 2-001 0.561 300.001 13.81 Tc (100) 1.001 0.001 1 0.70 0.0 3 8 LNGST. OVERL +CHANNEL 0.45 = Runoff C 1.00 = Cf 2,10 1.25 =Cf 100 D. Pnt. Area (acres) C Cf I (2yr.) (in/hr) I (10yr.) (in/hr) I (100yr.) (in/hr) Basin Q (Cfs) Comb. Q (cfs) COMMENTS 0.60 0.45 2.20 0.59 2 yr. runoff 0.45 3.80 1.03 p.m 10 yr. runoff 0.56 6.20 Z09 100 yr. runoff 0.45 = C 1.00 =Cf 2,10 1.25 =Cf(100) SUBBASIWT.'O.0 -4000yr). D. Pnt. Slope C Cf Length (feet) OverL Tc (min.) Vel.Chan (ft/sec. Tc Chan. min. Tc Total min.) COMMENTS 1.00 0.25 25.00 7.9 Tc (100) 1.30 0.00 2.25 0.0 1-9 LNGST. OVERL+CHANNEL 0.20 = Runoff C 1.00 = Cf 2,10 1.25 =Cf 100 D. Pnt. Area. (acres) C Cf I (2yr.) (in/hr) I (10yr.) (i n /h r) I 100yr.) (in/hr) Basin Q (cfs) Comb. Q (cfs) COMMENTS 0.77 0.45 2.70 0.94 2 yr. runoff 0.45 4.70 1.63 i 61 10 yr. runoff 7.00 3.031Ln'.�.XXXX�-:�:." 100 r. runoff 0.20 = C 1.00 =Cf(zlo) 1.25 =Cf 100 LU 1 ' i::.,)4 = Areatac) mis page 'SUBBASIN TOC. D. Pnt Slope DEVELOPED RUNOFF COMPUTATIONS FROM RATIONAL METHOD Q = C x Ct x I x A C Cf Length Overl-Tc Vel.Chan Tc Chan. Tc Total COMMENTS (min.) (tt/sec.) (min.) (min.) j(feet) 2.001 0.56 180.00 10.71 Tc (100) 1.001 - 0.00 200 0.00 7 LNGST. OVERL.+CHANNEL 0.45 = Runoff C 1.00 = Cf 2,10 1.25 =Cf 100 7L 91U�BBA51N,,.::T.LOC D. Pnt Slope I C*Cf I Length I overl-TC Vel.Chan Tc Chan. TcTotal COMMENTS % I (feet) I (min.) (ft/sec.) (min.) (min.) 3.001 0.561 - 260.001 11.2 1 Tc (100) 2.00 5.1 ." L ........ 16 3 LNGST. OVERL+CHANNEL 0.45 = Runoff C 1.00 = Cf 2,10 1.25 =Cf 100 SUBBASIN1O.C,-.1-: D. Pnt Slope % C Cf I Length feet ) Overl-Tc (min.) Vel.Chan I (ft/sec.) Tc Chan. (min.) Tc Total (min.) COMMENTS 3.001 - 0.56 260.00 11.2 Tc (100) 3.001 610.00 2.50 4.1 LNGST. OVERL.+CHANNEL 0.45 = Runoff C 1.00 = Cf 2,10 1.25 =Cf 100 D. Pnt. Area (acres) f I (2yr.) (in/br) I (10yr.) (in/hr) I (100yr.) (in/hr) Basin Q (cfs Comb. Q cfs) COMMENTS 3 1.2 0.45 2-10 1. 13 2 yr. runoff 0.45 3.76- 2.00 10 r. runoff 0.56 6.00 4.05 4.11 100 yr. runoff 0.45 = C 1.00 =Cf 2,10 1.25 =Cf(100) 4.86 = Area(aC) this page DATE: March 1994 HISTORIC/DEVELOPED RUNOFF COMPS. 2/10/100 YR. STORMS LINDEN ESTATES FOR: Z.T.I. GROUP BY: Stewart & Associates GENERAL NOTES: Velocity in a Channel per FIGURE 3-2 If C x Cf > = I then C x Cf = 1 (constants listed below) For design of the developed site runoff quantities Tc(l 00) was the basis for design D. Pnt. Slope C*Cf Length Overt Tc I Vel.Chan I TcChan. I TcTotal COMMENTS 3.701 0.311 200.001 13.51 Tc (100) ............ ... 0.001 1 0.001 1 2.001 0.001---,',-. ........ �.13 51 LNGST. OVERL.+CHANNEL = Runoff C 1.00 = Cf 2.10 1.25 =Cf 1 D. Pnt. Area (acres) C Cf I (2yr.) (in/hr) 1 (1 Oyr.) (in/hr) I (100yr.) (in/hr) Basin Q cfs Comb. Q cfs COMMENTS 2.58 0.25 2.75 1.77FTTTTTT81 2 yr. runoff 0.25 4.00 2.581 10 yr. runoff 0.31 6.40 5.16 00 yr. runoff 0.25 C 1.00 Cf(2,1 0) 1.25 =Cf(100) IMM 6.95 = Area this Page Storm Drainage Report' Lindenmeier Estates Page 5 CONCLUSIONS No risk to health or human safety are evident from the preliminary review undertaken. Concern of downstream property owners will be addressed and verified during final, though it does not appear as though any significant impact will result. Should question arise during your review of this report please do feel free to contact our office so we may facilitate your .. understanding. Respectfully, Richard A. Rutherford, P.E. & L.S. #5P28 b:\linden.rpt Storm Drainage Report' Lindenmeier Estates Page 4 Street capacities are well within the SDDCCS criteria and should present a concern during final design. Curb inlets will all be designed in a "sumped" condition to facilitate the maximum inlet capacity. It is anticipated that software developed for Urban Storm Drainage "UDSEWER" will be used to design the piped collection system. No landscaped areas within the site will be left with slopes of less than 2 percent that would require nuisance flow considerations. Offsite data will be required for much of the final design work though during this cursory review and based on available data the design concept is feasible. Data on the swale and down stream piping into the Lake will be the primary focus of further study. DETENTION Detention may not be required on this site, apparently the downstream structures are adequate. Though this fact will have to be verified in detail, before we will do a final design without detention. Also the owners of the Lindenmeier Lake, Water Supply and Storage, appear willing to accept the increase of storm flows from this proposed residential development. Storm Drainage Report' Lindenmeier Estates Page 3 This historic. runoff is directed primarily to two specific areas, the ditch on the West facing slope, and the existing 1 12" CMP crossing Lemay and running into Linden Lake. These points of release will be maintained following the proposed intensified usage. Rates will increase however, with the minor and major events now developing 13.3 cfs and 41.0 cfs. Basins 1 and U-1 will flow into the ditches while the remainder of the site will be collected and conveyed into Linden Lake. During this preliminary report, details of this split of flow has not been entirely developed. Noteworthy, is the fact that the single family residence O'Halloran property has been included in our design considerations: HYDRAULICS Piped and surface methods of runoff conveyance will be incorporated in this project. .Three curb inlets are being proposed, one each.on the North and South sides of Lindenmeier Place, and a third at the "low spot" along Lemay Avenue. These structures will direct flow into the existing 12" CMP and will be allowed to discharge into the Linden Lake. One area inlet will also be constructed that will serve as a junction for all of the aforementioned structures. Preliminary indications are that the 12" CMP may .require an increase in size too handle the 100 yr direct runoffs. Storm Drainage Report' Lindenmeier Estates Page 2 HYDROLOGY The site is unique in that most of the 6.95 ac do not flow offsite nor does offsite flow move onto this project area. There exist topographic features that function as effective hydraulic breaks. To the East is Lemay Avenue, which will not allow flows to cross the proposed center line elevations. Though flows from 150 ft North of the site and approximately the same distance South will be directed toward the newly constructed storm drainage collection system. South and West are two existing ditches that again do not allow flows on to or off the project area. The ditches will remain as the exist today following the construction of this development. North, is the irrigation canal operated by the Larimer and Weld Irrigation Company, again a substantial hydraulic barrier. Based on this information the isolation of this drainage area is evident. Historically, a large portion of the project area discharge into Lindenmeier Lake on the East Side of Lemay, during minor and major events rates of 3.8 cfs and 12.2 cfs respectively can be expected. These rate were established using the Rational Method, with a runoff coefficient "C"= 0.25 as shown in the Storm Drainage Design Criteria and Construction Standards (SDDCCS) for RLP zoning. The SDDCCS is the basis of all design through out this preliminary report. 6 PRELIMINARY STORM DRAINAGE REPORT FOR LINDENMEIER ESTATES GENERAL The proposed residential development is in the Northeast quadrant of Fort Collins (the City), Colorado, in Section 36, Township 8 North, Range 68 West of the 6th P.M. This is approximately 1/4 mile North of the North Lemay Avenue (Lemay), East Willox intersection, on the West side of Lemay. Currently, the site is zoned RLP and has not undergone any development activity. A dense grass and weed covered knoll describes the 6.95 ac existing site conditions, with slopes ranging from 2 to 5 percent. North of the site is the Larimer and Weld Irrigation Company Canal and the Puebla Vista Estates Subdivision. West is a single family residence and a proposed regional detention facility for the City. South is the Greenbriar Estates Subdivision, while East is Linden Lake Estates on the opposite side of Lemay. Proposed are 12 residential lots yielding densities of less than 2 units per acre. The site does not reside in any major drainage basin, but is isolated hydrologically to a large degree. Details of this isolation will be provided later in this report. r Preliminary Storm Drainage Report for Lindenmeier Estates March 1994 STEwArg;LAiSSocwTES Consultin3 En3ineers and Surveyors 103 South lle-Qditum •SdA"I Tort Cottins, Coloaado 80521 3031482-9331