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HomeMy WebLinkAboutDrainage Reports - 02/14/2002a Final ApprOved Report f -160L Data 2I-- 141-o2-- Major Amendment to the FINAL STORM DRAINAGE and EROSION CONTROL REPORT LEVON'S 2nd WAREHOUSE AND OFFICE BUILDING 300 BLOCK OF WEST HICKORY STREET CITY OF FORT COLLINS, CO Prepared December 10, 2001 Prepared For: Charles Meserlian North College Avenue Fort Collins, CO 80521 (970) 221-0700 Prepared By: Structured Engineering 318 East Oak Street Fort Collins, Colorado, 80524 Phone (970) 495-0810 Fax (970) 224-1314 ' December 10, 2001 Structured Engineering 318 East Oak Street Fort Collins, CO 80524 Phone (970)-495-0810 ' Fax (970)-224-1314 Mr. Basil Hamden Stormwater Utility ' City of Fort Collins PO Box 580 ' Fort Collins, Colorado 80522 ' Dear Basil, Attached is a Major Amendment to the storm drainage report for Levon's ' 2nd Warehouse and Office Building P.D.P. This report revises the earlier report, dated May 7, revised June 18, and approved by the Fort Collins Stormwater Utility July 26, 2001. Because of the strong potential for a school being at least a partial tenant in the speculative building, the Poudre Fire Authority, the Fort Collins transportation ' staff and others have requested that moderate revisions to the interior drives and parking be performed to facilitate smoother traffic and pedestrian circulation. This report addresses the impact the associated increase in paving area will have on ' runoff. Additionally, inspection of the existing cross pan in Hemlock Street at the southwest corner of the site indicates there is insufficient capacity to pass 133% of the historical release without overtopping the pan. Accordingly, it is now proposed to replace the pan with a new one that has the capacity to pass 133% of Q 100. ' This report utilizes a portion of the calculations included in the previous report. Copies of those calculations with appropriate revisions are attached herein as part of this report. All design, except where variances are requested herein, is in conformance ' with the latest edition of the City of Fort Collins' Storm Drainage Design Criteria and. Constr ctio Standards and uses the latest precipitation rates. RE gyp••.....••, inc e y, •^ AgCi�•ss�i� ' 27979 Jo h P. o sky, P.E. =ate Structured E ding m••��o�'da• +�au�enuuah ...... \ R¢Nra w �• vi \ Butte \ r \ iarrl (eta 3 i 10 \ Rienbne P i °•� COLLINS.' \ \ 2 r+ Tama R. ° ri rj°° near RADO m °. o ,_. e -¢ olw.o0 �I \ e a C° C... r. t1} w e {7 0 300� 2000 ji JANUARY I, 1993- � 3...1.1.• L. • W Wille• '. ona Ln h�'b� N ` 0 ' e y W u W.I. \ st ° ° 1, Brempleeusp �! { t; It o n, iF Dt00. 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M - Gt °•� •v mt`or• _ w PL ��3 o rrlb 3t '^ \ c Bmtre < Birth lc Nc. St 10. i \ Laurel 1 SLo N , Q- St E g , Save P. \\ u.i E. E•ur N a - Sr Norin 0, - .Ole Imo Pivm St. Or .1 4: Ct. w. Elitee•rn St, < Imro • Or Lec..t SL Cr Place I E. Elltae.rn E ClLevteale _ Av T e i SovrE Or ....0 Go Sr r q, T West •e re Dr - � Or I Major Amendment to the FINAL STORM DRAINAGE and EROSION CONTROL REPORT for Levon's 2nd Warehouse and Office Building ' December 10, 2001 ' INTRODUCTION ' A second warehouse - office building is proposed for construction on a 3.36 acre (gross, 3.29 acres net after street R.O.W. dedications) parcel, zoned CN, for 'Commercial -.North College', in the 300 block of West Hickory Street. The parcel is just west of Union Pacific railroad tracks, south of Hickory Street and-horth of Hemlock Street. There is an existing 14,700sf warehouse on the property. This report sums up the analysis that was undertaken to determine what impacts construction of a new 20,000sf speculative warehouse will have on current drainage patterns in the area. ' The report addresses the following: 1 .Site Descriptions ' 2.Storm Drainage A. Design Criteria B. Hydrology ' C. Conformance With Existing Master Drainage Plans D. Proposed Drainage Improvements 3'.Erosion Control A. Erosion Control Measures ' The recommendations found in this report are an integral part of the design documents. •► The property is described as "a parcel of land being a portion of Block 15, the vacated alley therein, vacated Fourth Street and vacated Fourth. Avenue, in Riverside Park of the City of Fort Collins, and other property in ' the SE 1/4 of Section 2, Township 7 North, Range 69 West of the 6th Principal Meridian, in Larimer County, Colorado". The parcel has been re - platted as "First Replat of Levon's Minor Subdivision". The new building will be located in a presently undeveloped portion of ' the site. There are about a half dozen mature trees on this portion of the site... large diameter poplars. The remaining vegetation consists of local, native grasses or bare ground. ' A public concrete bike/pedestrian trail borders the site along the west side (offsite), and the Union Pacific railroad tracks are along the east side. tHemlock Street forms the south boundary, and Hickory Street the north. The proposed building, (approximately 80' x 250'), will be about 20' ' north of the south PL and about 78' from the west property line. Existing lot grading is at an approximate .4% slope, generally from the north to the south. ' Hickory Street is paved and has vertical curb and gutter. Hemlock Street along the south property line is gravel now and will remain so. No street access is going to be provided to or from Hemlock Street as part of these improvements. There is a concrete cross pan across Hemlock Street ' near the southwest corner of the building site. This pan was constructed as part of Phase 1 to pass 9.98 cfs. ' There are no pronounced natural drainage features on or adjacent to the site except for an existing swale that parallels the UP railroad tracks. ' The soils group making up the site is primarily clay loam according to the Larimer County Soils Survey by the Soil Conservation Service. A soils report prepared by Earth Engineering Consultants April 5, 1996 (EEC Project ' No. 1962025) for the first building more specifically defines the on -site material as a sand and gravel granular material. 1 1 11 A. Design Criteria The City of Fort Collins has prepared a Storm Drainage Design Criteria and Construction Standards (SDDC) which provides the basis for the analysis used in predicting storm runoff and the recommended drainage improvements. The latest precipitation rates have been used. B. Hydrology The Rational Method is used to predict the amount of peak runoff. The 100-year return frequency was used in this report to predict major peak discharges, and the 10-year storm is analyzed for the minor storm. C. Conformance With Existing Master Drainage Plans The FIRM Flood Insurance Rate Map prepared by FEMA ( Community Panel Number 08012-004-C, revised March 18, 1996) was consulted to determine flood plain boundaries in the area. The flood plains are indicated . on sheet 3 of the utility drawings, and are also included in this report. In summary, the proposed building site is not impacted by any existing floodplain. ' Because the site is located in the Poudre River Drainage Basin, the Storm Water Utility does not require on -site detention to maintain historical release rates. D. Proposed Drainage Improvements Site grading will generally allow storm run-off to maintain existing sheet flow patterns.. Concentrations of run-off will be avoided to keep run- off velocities very low, assisting in percolation and infiltration into the on - site sand and gravel materials. Existing conditions are flat and do not allow the customary 2% min. slope for earthen drainage, and there may be areas of standing water for brief periods of time after severe storms. The Owner is willing to accept this condition, and is asking the Stormwater Utility to grant a Variance for a minimum .40 % grade due to existing conditions. The Owner is also requesting that fill areas be allowed to be constructed with 3:1 side slopes in lieu of the recommended 4:1 slope to diminish the amount of fill required to raise the building pad. Proposed drainage improvements will consist primarily of filling and grading the site to direct runoff to the southwest corner of the site. RCP ' pipes, structural class IV, will be installed on -site to transport runoff from the north and east portions of the site beneath the entry drive and parking ' areas to the southwest corner of the site. The Stormwater Utility requires that accomodations be provided to ' ensure that runoff water is not polluted with nitrates, oils, sediment and other deleterious materials that could harm receiving waters. The general concept is to retain the initial flush of runoff to allow such matter to settle ' out or percolate into the ground, rather than discharging the matter into downstream -waterways. The recommended method is to provide orifice plates at a headwall to detain a certain volume of runoff, ( a water duality capture Volume, or WOCO, discharging it slowly over 40 hours. A problem arises when the release rate is very small, (slow), resulting in quite small . orifice perforations that are susceptible to clogging. Structured Engineering ' has chosen to utilize a rectangular weir plate of comparable discharge rate in lieu of individual circular orifices. It is expected that such a weir will perform the same function as the orifice plate with less likliehood of . ' clogging completely. Therefore, prior to leaving the site, runoff quality will be improved with temporary detention behind a WQCV weir. The clarified runoff will be released over a 40hr time period through the calibrated weir. The historical 9.98 cfs 100yr release rate will overtop the WQCV ' detention weir and cross Hemlock Street in a new cross pan designed to pass 133% of the flow (13.33 cfs) that will be constructed as part of these ' improvements. Runoff then will sheet flow to the Poudre River across the Salyer Open Space in an existing 150' wide drainage easement. The difference between the 9.98 cfs historical flow and the 16.40 cfs now anticipated due to the proposed development will be detained on site. A total of 10312 cubic feet of runoff will be detained, which includes a WQCV of 3117 cubic feet. With the full 10312 cf in storage, ie; assuming the . WQCV storage is already full when the 100yr storm occurs, the 100yr WSL ' in the detention pond will be at elevation 4974.30. Raising the top elevation of the containment berm to ele. 75.0 maintains the 9" of freeboard ' accepted by variance in the previous report. Brim full capacity of the detention pond is estimated at 19400 cf or 188% more volume than is required for actual storage purposes. ' Elsewhere, in the southeast corner of the site, re -grading results in less runoff discharging south along the Union Pacific RR than historically. ' Hence, no further discussion is warranted here. 1 11 I :• •11KIKOHIM19111 The SDDC outlines the causes and results of soil erosion due to wind and rain. Along with the requirements of this report and the erosion control plans, the SDDC shall be considered in it's entirety for guidelines to ' aid in preventing rainfall and wind soil erosion. The SDDC will govern requirements and specifications for earth moving and other construction at the site. ' Until permanent seeding is established, straw bale dikes will be constructed to cause any loose, fine grained soils transported by surface ' runoff to settle out. Along the south property line and a portion of the west property line, temporay silt fences will be constructed to prevent sediment from being deposited upon the public right of way in the event of heavy ' rains. The fence also will act somewhat as a wind barrier, keeping low blowing fugitive dust from leaving the site. As field operations continue, ' disturbed areas will have hay mulch disced into the ground to provide cohesiveness to the soils. Where disturbed areas are to be of very short term, discing ridges perpindicular to the prevailing winds may be ' substituted. Below are general erosion control requirements which the contractor will be required to follow. ' As required, a cost estimate for an erosion control security escrow is included with this report. A. Summary of Erosion Control Requirements t The following is a summary of the storm drainage improvements and erosion control measures that will be adhered to during construction. ' GENERAL EROSION CONTROL REQUIREMENTS The City of Fort Collins Stormwater Utility erosion control inspector must ' be notified at least 24 hours prior to any construction on this site. All required perimeter fencing shall be installed pAor to any land ' disturbing activity (stockpiling, stripping, grading, etc.). All other required erosion control measures shall be installed at the appropriate time'in the construction sequence as indicated in the approved project schedule, construction plans, and erosion control report. Pre -disturbance vegetation shall be protected and retained wherever possible. Removal or disturbance of existing vegetation shall be limited to the area required for immediate construction operations, and for the ' shortest practical period of time. • All soils exposed during land disturbing activity (stripping, grading, utility installations, stockpiling, filling, etc.) shall be kept in a roughened . condition by ripping or discing along land contours until.mulch, vegetation, or other permanent erosion control is installed. No soils in areas outside project street rights -of -way shall remain exposed by land disturbing activity for more than thirty (30) days before required temporary or permanent erosion control (e.g. seed/mulch, landscaping, etc.) is installed, unless otherwise approved by the Stormwater Utility. • The property shall be watered and maintained at all times during construction activities so as to prevent wind -caused erosion. All land disturbing activities shall be immediately discontinued when fugitive dust impacts adjacent properties, as determined by the City of Fort Collins ' Engineering Department. ' • All temporary (structural) erosion control measures shall be inspected and repaired or reconstructed as necessary after each runoff event in order to assure continued performance of their intended function. All retained sediments, particularly those on paved roadway surfaces, shall be removed and disposed of in a manner and location so as to not cause their release into any drainageway. ' • No soil stockpile shall exceed ten (10) feet in height. All soil stockpiles shall be protected from sediment transport by surface roughening, watering, and perimeter silt fencing. Any stockpile remaining after 30 days shall be seeded and mulched. ' City Ordinance prohibits the tracking, dropping or depositing of soils or any other material onto City streets -by or from any vehicle. Any ' inadvertently deposited material shall be cleaned immediately by the contractor. :• •► •► 19;161 II&IX0111M :• A : • 11 Attached is the cost estimate for the erosion control escrow required by the proposed construction of a warehouse -office building in the 300 block of West Hickory Street (Levons 2nd Warehouse and Office Building). 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' Design Storm: tQO yf Rev Notes: By: JAM ' Area: 3`639 acres Cf: 1 25 Comp. "C": U 62 Allow. Release rate:]::::9,9.8,., cfs Cf x C: 0.78 (Cf x C <=1) Inflow Allowable Difference ' 100yr "Q" cfs Volume In (c.f.) Release (Storage Req'd) Minutes "i" ("Q"=CfCiA) Q x seconds Volume c.f. c.f. ' 5 8 9.95 8.38 28.06 23.63 8418 11344 2994 4790 5424 6554 10 7.72 21.77 13063 5988 7075 12 7.16 20.19 14539 7186 7353 ' 14 6.71 18.92 15896 8383 7513 16 6.30 17.77 17057 9581 7476 ' 18 5.92 1630 18031 10778 7253_a 7pq �c 20 5.60 15.79 18952 11976 6976 = IS• Q w�irt S 22 5.32 15.00 19805 13174 6631 ' 24 5.09 14.35 20671 14371 6300 26 4.87 13.73 21426 15569 5857 28 4.69 13.23 22221 16766 5455 30 4.52 12.75 22945 17964. 4981 32 4.33 12.21 23446 19162 4285 34 4.16 11.73 23934 20359 3574 ' 36 4.01 11.31 24428 21557 2871 38 3.87 10.91 24885 22754 2130 40 3.74 10.55 25314 23952 1362 42 3.62 10.21 25727 25150 578 44 3.51 9.90 26133 26347 ' 46 3.41 9.62 26543 27545 48 3.31 9.33 26885 28742 50 3.23 9.11 27328 29940 ' 52 3.14 8.86 27629 31138 54, 3.07 8.66 28052 32335 56 58 2.99 2.92 8.43 8.24 28333 28658 33533 34730 60 2.86 8.07 29037 35928 I Prepared by Structured Engineering 318 East Oak Street Fort Collins, CO 80524 Ph. (970) 495-0810 Trapezoidal Channel Capacity DateLocation Actual Flow Read8> CFS ...........:::: Design Flow CFS Notes: lefet'aia1ii f8r €°1a Printed 11/05/01 at 02:43:41 PM Enter n, s, Z-left, Z-right, b, and Q=(1.49/n)"(((A/P)^.667)'A'(S^.5) OR, use "Goal Seek" if there are fixed constraints I ZZ'�e n A P R s (ft/ft) Z left Z right b Depth of Flow 1.779 18.868 0.094 Comments# ati sj"carEcf RW t IM Q1,;0 I / ' zo sFL t u 1 of 1 FLTBOTCH.123 Prepared by Structured Engineering 318 East Oak Street Fort Collins, CO 80524 Ph. (970) 495-0810 Trapezoidal Channel Capacity PateLocation CFS Notes: Printed 11/05/01 at 02:47:34 PM Enter n,'s, Z-left, Z-right, b, and Q=(1.49/n)"(((A/P)^.667)'A"(s^.5) OR, use "Goa/ Seek" if there are fixed constraints n A P R s (ft/ft) Z left Z right b Depth of Flow 0.55a 10.562 0.053 CommentsFYatai3;Ffc#eft>�?�(i:r l 1of1 FLTBOTCH.123 No Text Prepared by Structured Engineering 318 East Oak Street Fort Collins, CO 80524 Ph. (970) 495-0810 Printed 10/30/01 at 02:55:26 PM FLTBOTCH.123 [1 Prepared by Structured Engineering 318 East Oak Street Fort Collins, CO 80524 Ph. (970) 495-0810 ' Trapezoidal Channel Capacity ' ec Date Location Actual Flo1 Aes*an Flo Notes: Printed 11/05/01 at 07:30:09 AM 1 of 1 FLTBOTCH.123 01 / 18/2002 01:33:39 PM Structured Engineering 318 East Oak Stree Fort Collins, CO 80524 (970)495-0810 Date: 01 / 18/2002 Project: Levon's 2nd Location: 100yr release at SW corner of property Notes: Find length to pass 9.98 cfs given .80' head (MAX. RELEASE RATE) AS SUPPRESSED BROAD CRESTED WEIR Q=2/3*C*B*((2*g)11/2)*((H)^3/2) (Lindeburg Eqn. 5.26) where: C=[.6035+.0813(H/Y)+.000295/Y]*[1+(.00361/H)]^3/2 ................................. Given H ? ;; 0 80 .:: i I feet, water depth above weir IQ7Y2W5�- Top wvvf' -7A.3o - 73,%:-&Q Given Y ? 0 88 feet, water depth from channel invert to overflow Find C 0.682 13,50 72 12. .88 When B f 3 82 feet Then Q = 9.98 cfs 4� '100,klel r2= - - I�73,50 I d � a 1°µ91L I Page 1 of 1 RECTWEIR.123 = 75,D FLA, u ; / ' a a '1� Q L'�11�P-Pt fta (Z3 0) NA« CJcJjk Z.75 J �Jei' Z3?5 4149 u 61 1 1c 2us � �o-55 s C2,5) li ae CL - i 1 1 i 1 - 1 1 Fr.-i'p - litapv I ilc A �, e—, � BUJ40t-l�,, �Lf LA(54, .7-1<1,1 L 1z. an ff(9 171 C -77�-4- 5 P:z 0 Prepared by Structured Engineering 318 East Oak Street Fort Collins, CO 80524 Ph. (970) 495-0810 Trapezoidal Channel Capacity Proaec SM Date Location E$tesf'' US Notes: Enter n, s, Z=left, Z-right, b, and Q=(1.49/n)'(((A/P)^.667)'A`(s^.5 OR, use "Goal Seek" if there are fixed constraints Printed 06/15/01 at 02:11:44 PM G 0 1of1 FLTBOTCH.123 EFFECTIVENESS CALCULATIONS ------=------------------------------------------------------------ PROJECT:� - {� �,_=lc.t} r,� Z � a� STANDARD FORM B COMPLETED BY: DATE: Erosion Control Method /j ----------- -------- St �rr� ---- s MAJORI PS SUB I AREA BASINI (w) IBASINI (Ac) ----- I ---- --I ----- 1----- 7 3r1. il�% C-Factor P-Factor Value --------Value Comment I -------- 6y, 5+1 N 5 3� 1.42��� s-ice Q.3�%• I I r0 1,0 lets M1�"'�Cvl fA�1Cr✓r� t I Gr & fet,. rkiv IN G , - _-�--------� - -----------------------------I I. 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