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Home My WebLink AboutASPEN HEIGHTS - Filed GC-GENERAL CORRESPONDENCE - 2016-06-09City of F6rt Collins September 23, 2013 Larry C. Owen, P.E. Owen Consulting Group, Inc. 3715 Shallow Pond Dr. Fort Collins, Co 80528 Planning, Development & Transportation Engineering Department 281 North College Avenue P.O. Box 580 Fort Collins, CO 80522.0580 970.221.6605 970.221.6378 - fax fcgov. com/engineering Re: Aspen Heights - variance for driveway setback and cover over utility lines in the streets Dear Larry, This letter is in response to the two variance request letters sent to me dated July 1, 2013 regarding a variance request to the minimum off street parking setback distance and (Fig 19-6) and to Section 12.2.2 regarding the minimum depth requirement for utilities. I will address each of the variance requests as I understand them to be: 1. The variance request to reduce the parking setback from 50 feet to 40 feet is granted. 2. The variance request to reduce the cover over the NECCO pipes under Lupine Street to 1.6 feet (from top of pipe to top of asphalt at the north flowline) is granted with the condition that the street area over the pipes is constructed in concrete from a point approximately 20 feet east of the pipes to a point approximately 20 feet west of the inlets located west of the NECCO pipes. 3. The variance request to reduce the cover over the storm pipe crossing on Blue Spruce Drive, just north of New Vine Drive, to 2.5 feet is granted pr6vided that the concrete cross pan at this intersection is extended north so that the concrete street extends approximately 20 feet north of the storm pipe. 4. The variance request to reduce the cover over the interim storm pipe in Redwood Street is granted on the basis that at such time as the ultimate improvements are constructed that the portion of the pipe system that does not meet minimum cover requirements is removed at that time. These requests does not set precedence or change the application of our design standards in other situations. If you have any questions, please contact me at 221-6573. Sincerely, Sheri L. Langenberger, P.E. Attachments cc: Ted Shepard, City of Fort Collins file Culvert Calculator Report Aspen Heights - Lupine Street Culverts Solve For. Headwater Elevation Culvert Summary Allowable HW Elevation 4,964.00 ft Headwater Depth/Height 1.81 Computed Headwater Elev, 4,962.81 ft Discharge 159.40 efs Inlet Control HW Elev. 4.962.44 ft Taiiwater Elevation 4,960.54 ft Outlet Control HW Elev. 4,962.81 ft Control Type Outlet Control Grades Upstream Invert Length 4,959.18 ft 124.00 ft Downstream Invert Constructed Slope 4,958.80 ft 0.003065 ft/ft Hydraulic Profile Profile CompositeM2PressureProfile Slope Type Mild Flow Regime Subcritical Velocity Downstream 8.44 ft/s Depth, Downstream Normal Depth Critical Depth Critical Slope 1.74 it N/A it 1.74 ft 0.007616 ft/ft Section Section Shape Horizontal Ellipse Section Material Concrete Section Size 24x38 inch Number Sections 4 Mannings Coefficient Span Rise 0.013 3.15 ft 2.00 ft Outlet Control Properties Outlet Control HW Elev. Ke 4,962.81 ft 0.20 Upstream Velocity Head Entrance Loss 0.95 It 0.19 ft Inlet Control Properties Inlet Control HW Elev. 4,962.44 ft Grooieiehlsy"h headwall (horizontal ellipse) K 0.00180 M 2.50000 C 0.02920 Y 0.74000 Flow Control Area Full HDS 5 Chart HDS 5 Scale Equation Form Submerged 20.4 ft2 29 2 1 Project Engineer. LARRYOWEN8BBFWdministrator main channel culverts under lupine - revised 12-02... CAME Academic SitsExton CulvertMaster v3.3 [03.03.00.041 Culvert Calculator Report Aspen Heights - Lupine Street Culverts Solve For. Headwater Elevation Culvert Summary Allowable HW Elevation Computed Headwater Elevi Inlet Control HW Elev. Outlet Control HW Elev. 4,964.00 ft 4,965.77 It 4,964.93 ft 4,965.77 ft Headwater Depth/Height Discharge Tailwater Elevation Control Type 3.30 239.67 cfs 4,960.98 it Outlet Control Grades Upstream Invert Length 4,959.18 it 124.00 it Downstream Invert Constructed Slope 4,958.80 it 0.003065 Wit Hydraulic Profile Profile PressureProfile Slope Type N/A Flow Regime N/A Velocity Downstream 11.75 ft/s Depth, Downstream Normal Depth Critical Depth Critical Slope 2.18 it N/A ft 1.93 ft 0.017022 ft/ft Section Section Shape Horizontal Ellipse Section Material Concrete Section Size 2038 inch Number Sections 4 Mannings Coefficient Span Rise 0.013 3.15 it 2.00 It Outlet Control Properties Outlet Control HW Elev. Ke 4,985.77 It 0.20 Upstream Velocity Head Entrance Loss 2.15 It 0.43 it Inlet Control Properties Inlet Control HW Elev. 4,964.93 It Gkbtf XW projecting (horizontal ellipse) K 0.00450 M 2.00000 C 0.03170 Y 0.69000 Flow Control Area Full HDS 5 Chart HDS 5 Scale Equation Form Submerged 20.4 f 2 29 3 1 Project Engineer: LARRYOWENSBBFkAdministrator main channel culverts under lupine - revised 12-02... CAME Academic 81teExton CulvertMaster v3.3 (03.03.00.04] C..1.+� 1YrfZf' Air I AW 0,,440W'7dGE 11A1 Culvert Calculator Report Aspen Heights - Lupine Street Culverts Solve For: Discharge Culvert Summary Allowable HW Elevation 4,964.00 ft Computed Headwater Elevi 4,964.00 ft Inlet Control HW Elev. 4,963.20 ft Outlet Control HW Elev. 4,964.00 ft Grades Headwater Depth/Height 2.41 Discharge 190.28 cis Tailwater Elevation 4,960.98 ft Control Type Outlet Control Upstream Invert 4,959.18 ft Downstream Invert 4,958.80 ft Length 124.00 ft Constructed Slope 0.003065 ft/ft Hydraulic Profile Profile PressureProttle Depth, Downstream 2.18 ft Slope Type N/A Normal Depth N/A ft Flow Regime WA Critical Depth 1.84 ft Velocity Downstream 9.33 NO Critical Slope 0.010555 ft(ft Section Section Shape Horizontal Ellipse Mannings Coefficient 0.013 Section Material Concrete Span 3.15 ft Section Size 24x38 inch Rise 2.00 ft Number Sections 4 Outlet Control Properties Outlet Control HW Elev. 4,964.00 ft Upstream Velocity Head 1.35 ft Ke 0.20 Entrance Loss 0.27 ft Inlet Control Properties Inlet Control HW Elev. 4,963.20 ft Flow Control Submerged Groalslairl5joh headwall (horizontal ellipse) Area Full 20.4 ft' K 0.00180 HDS 5 Chart 29 M 2.50000 HDS 5 Scale 2 C 0.02920 Equation Form 1 Y 0.74000 Project Engineer. LARRYOWEN8BBFWdministrator main channel culverts under lupine - revised 12-02... CAIHE Academic SiteExton CulvertMaster v3.3 [03.03.00.04) Aspen Heights - Street Overtopping at Lupine Culverts - Interim Project Description Solve For Headwater Elevation Input Data Discharge 49.39 ft'!s Crest Elevation 4964.00 ft Tailwater Elevation 4960.98 ft Crest Surface Type Paved Crest Breadth 30.00 ft Crest length 55.00 ft Results Headwater Elevation 4964.45 ft Headwater Height Above Crest 0.45 ft Tailwater Height Above Crest -3.02 ft Weir Coefficient 3.00 US Submergence Factor 1.00 Adjusted Weir Coefficient 3.00 US Flow Area 24.61 ft2 Velocity 2.01 ft/s Wetted Perimeter 55.89 ft Top Width 55.00 ft 61261201312:43:20 PM Bentley Systems, Inc. Haested Methods SO M0ti0061wMaster V814SELECTsedes 1) [08.11.01.03) 27 Slemons, Company Drive Suite 200 W Watertown, CT 06786 USA +1-203-766-1666 Page 1 of 1 INTERIM OUTFALL CROSSING OF REDWOOD ST. ALTERNATE PROFILES Alignment — (STORM 500) — (22) STA:—0+50.00 THRU 1+50.00 -0+50 4970 -4-- STATION TOP = 4956.75t IE IN - 4952.75 IE IN = 4952.75 IE OUT = 4952.09 PIPE - (505� 90 LF OF 19 X3O' FRCP 4960 a O.2O9 GRADE. N M11 STOW MANHOLE 11MM, TOP = 4957.25t IE IN = 4951.41 IE IN = 4951.90 IE OUT = 4951.41 FFPIIPE - (316) ' PVC AN. SEWER 4 1+00 1+50 I ' 4970 4960 mm=�11� :in■■■■ �.i11�1A11■ =�■■WPAI �■■ - -. PIPE - _(Mn--L O 0.5Ox GRAD r INLET - (5O6) STA 1+30 06 C DITCH INLET M = 4954.64f UT = 4952.93 4940 4940 —0+5b 0+00 1+00 1+50 STATION ,b-� arm w reset-e- ..-yn, `v� COWEN CONSULTING MEMORANDUM To: Meeting participants per introductory paragraph CC: From: Larry C. Owen, P.E. Date: May 17, 2013 Proj. No.: 11-358 Project Name: Aspen Heights Subject: Mtg with City Staff re Dry Creek Floodplain and CLOMR (5-14-13) Following are notes of a meeting with City staff regarding the Dry Creek floodplain and the need and responsibility for preparation of a Conditional Letter Of Map Revision (CLOMR) addressing the impacts to the currently mapped floodplain due to construction of road and related improvements within the floodway. Attendees at the meeting included, from the City of Fort Collins, Marsh Hilmes-Robinson, Jon Haukaas, Glen Schlueter, Sheri Langenberger; from Poudre Fire Authority, Jim Lynxwiler; from Aspen Heights, Ryan Fetgatter, Robert Scholz, Fred Munoz; and from the consultant team, Lucia Liley, Rich Shannon, Larry Owen. 1. City Staff opened with the position that the CLOMR must be approved before the Utilities Plans can be approved, and no construction of public improvements can be commenced until the Utilities Plans are approved. 2. Construction of New Vine Drive and Redwood Street will impact the area mapped by FEMA as floodway, and thus a CLOMR is required. 3. The CLOMR must reflect the changing hydrology upstream of the mapped floodway, as well as the impacts to the floodway due to surface changes within the floodway associated with the proposed construction of New Vine Drive and Redwood Street. 4. The analysis and engineering associated with the CLOMR must also consider possible impacts to downstream and adjacent property. Changes due to construction in the existing floodway / floodplain cannot exacerbate flooding in the Old Town North property or any properties downstream of Redwood Street and the Lake Canal. a. Downstream property owners (Raptor Center, Alta Vista subdivision) are apparently concerned about putting water back into the Dry Creek channel. b. Seme-The Raptor Center, a downstream property owners hasve made modifications to the Dry Creek channel, supposedly to alleviate seepage, and these modifications niay have Fedused eliminated the low flow the -capacity of the channel so the to Gamey anticipated larger storm flows will enter the old Dry Creek channel only after the Lake Canal capacity is exceeded. 5. The engineering associated with the construction of New Vine Drive and Redwood Street must provide for conveyance of flood flows beneath Redwood St., but not beneath the Lake Canal a. Low flows can be discharged into the Lake Canal, as happens now. 3715 Shallow Pond Dr., Fort Collins, CO 80528 - Phone (970) 226-0264 • Fax (970) 226-3760 Aspen Heights Student Housing Notes of 5-14-13 Mtg with City Staff re CLOMR Page 2 of 4 b. High flows can overtop the Lake Canal (assumes that the Lake Canal will be flowing at capacity at this stage) and pass into the downstream Dry Creek channel, again as currently happens. c. These discharge scenarios are considered to be historic conditions. 6. The Developer's team expressed concern that the time required to process the CLOW through the City and FEMA reviews would unduly delay, and potentially kill the student housing project. a. It was pointed out that because of the student housing nature of this project, there is an inflexible completion date for the project. b. If the houses comprising the project are not ready for occupancy in August of the target year, prior to students returning to start classes, the next opportunity to lease the accommodations is one full year later. Such a delay would be a fatal flaw. 7. The consultant team reiterated their previous understanding that processing of the CLOMR and City review and approval of the construction activities that would impact the current floodplain (specifically, construction of New Vine Drive and Redwood Street) could be separated from the remainder of the project (possibly in a separate stand alone filing), such that approval and construction of the public and private improvements outside the floodplain boundaries could proceed concurrent with the processing of the CLOMR. City staff agreed that this is possible only through the PDP stage. The utility plans must be completed, which includes the CLOMR and final design approval before the project can proceed to the DCP (Development Construction Permit) stage. 8. The consultant team stated that the proposed improvements to New Vine Drive and Redwood Street are not necessary to accommodate the traffic that will be generated by the Aspen Heights development, and that a preliminary assessment of traffic impacts, without improvements to either of those two streets, indicated continued satisfactory operation of the existing streets and intersections that would receive the site -generated traffic. Such a traffic study has not been submitted to or reviewed by the City. 9. A request was made again that the work within the floodplain be separated from the balance of the project work, in order to allow review and approval of the majority of the project to proceed. It was clarified that the developer is not seeking to avoid making the off -site improvements; only to avoid a delay that would jeopardize the whole project. 10. Jon Haukaas indicated that he is willing to look at phasing of the project, provided that City requirements are met. He reiterated that the City will -cannot sign off on public improvements that are linked to the CLOMR until the CLOMR is approved_; This is a FEMA requirement and it could OR GFdeF to avoid the possible need to remove and replace constructed improvements in the event that FEMA's review of the CLOMR identifies needed design revisions. 11. In further discussions of the ramifications of delaying the construction of New Vine Drive and Redwood Street, concern was raised regarding the lack of a second access to the portion of the proposed development in the southwest quadrant of the property that would most closely be served by the proposed intersection of Blue Spruce Drive and New Vine Drive. There was speculation that Poudre Fire Authority may restrict development of that southwest quadrant until such time as the second access is completed. Aspen Heights Student Housing Notes of 5-14-13 Mtg with City Staff re CLOMR Page 3 of 4 12. Jim Lynxwiler (PFA) was asked to join the meeting, and after examining the development plan and discussing the situation with City staff and the development team, concluded that PFA would likely allow development to proceed throughout the entire site, on the condition that a second means of emergency access is provided to the southwest quadrant of the site. Two possible emergency access options were discussed and determined to be acceptable: a. Complete Blondel Street in Old Town North (OTN) and a sufficient portion of New Vine Drive to provide an acceptable link across to the south end of Blue Spruce Drive in Aspen Heights. This option would likely require finished construction of the full cross- section of Blondel Street and opening of the street to public traffic. The City would probably not allow gating off of a road (even a gravel surfaced road) within a dedicated public right-of-way. (Really? I thought Sheri was going to check to see if it could be gravel if it was gated for emergency access. Mavbe there have been conversations since the meeting.) b. Construction of a temporary emergency access way from Lupine Drive to Echo Mountain Lane, at the northeast corner of the southwest quadrant of the project site. This temporary emergency access would have to have an all-weather surface, capable of supporting fire apparatus. 13. Jim acknowledged that PFA will have adequate access to the site from east and west along Conifer Street, without completion of Redwood Street. 14. Further discussion of a separation and temporary deferment of the construction of New Vine Drive and Redwood Street led to the following requirements and agreements between City staff and the Developer's team: a. The Developer must demonstrate, via a TIS addendum, that the absence of New Vine Drive and Redwood Street will not result in an unacceptable Level of Service (LOS) on existing nearby streets or at existing intersections (Conifer / Redwood, Conifer / Blue Spruce, Conifer / College). b. The Developer must assure the City that the proposed New Vine Drive and Redwood Street improvements will be constructed as soon as possible. It was indicated by the Developer that this work would, in all likelihood, be completed prior to the issuance of iY -keCertificates of Occu ancy for the houses within Aspen Heights, c. In order for the City to process the New Vine Drive and Redwood Street improvements separately from the balance of the project, these will likely have to be treated as a separate filing, so that the FDP submittal for the first filing can be approved and processed. Elements of work in the second filing would include the road improvements and the associated storm drainage infrastructure. d. Underground utilities within the floodplain could be approved by the City and constructed prior to approval of the CLOMR, provided that the existing ground surface within the floodplain is restored exactly to preconstruction conditions. This would require a detailed survey, prior to commencement of construction and careful restoration of all disturbed areas. A City -issued Floodplain Use Permit would be required and a Zero Rise Certification of flood elevations. e. The underground utilities that could be installed under the Floodplain Use Permit include the water main in Vine Drive and the outfall piping from the interim detention basin along Redwood Street to the discharge point at the Lake Canal. Aspen Heights Student Housing Notes of 5-14-13 Mtg with City Staff re CLOMR Page 4 of 4 15. Finally, there was discussion regarding the need to ensure that the work within the New Vine Drive and Redwood Street rights -of -way that is subject to URA funding is commenced prior to the deadline set out in the URA Development Agreement. Since the CLOMR is covered under the URA funding agreement, it must be completed within the prescribed time frame. CG OWEN CONSULTING GROUP, INC. July 1, 2013 City of Fort Collins Engineering Development Review 281 N. College Ave Fort Collins, CO 80522 Attention: Ms. Sheri Langenberger RE: Aspen Heights Student Housing Driveway Area Setbacks Dear Sheri, Project File #: 11-385 Following is a synopsis of the analysis done to determine the required setbacks for the respective off-street parking areas within the Aspen Heights Student Housing project. The analysis demonstrates that a setback of 40 feet is appropriate for all but two of the parking areas. A Modification of Standards is requested for those two parking areas. The Traffic Impact Study (TIS) prepared for the project predicts that the Average Daily Trip (ADT) total that will be generated by the development will be 2,180 vpd, based on a resident population of 716 students. The ADT total is equivalent to 3.04 trip ends per day per student. The daily traffic volume to and from the respective parking areas is calculated based on the number and type of housing units served by that parking area and the student occupancy rate of the respective buildings. The attached spreadsheet (Sht 1 of 2) demonstrates that no parking area driveway has an ADT greater than 750. All parking areas are accessed from public streets classified as "local". Thus, per LCUASS Figure 19-6, the required setback distance from the street flow line to the nearest parking stall will be determined by the average daily traffic volume in the adjacent street. For this analysis, distribution of the total predicted site generated traffic to the local streets in the development area (Lupine Drive and Blue Spruce Drive) is taken to be proportionate to the peak hour traffic volumes at the access points, as presented in the TIS. The spreadsheet attached shows that approximately 26% of the daily traffic (561 ADT) will access the site via Conifer Street and Blue Spruce Drive North; approximately 22% of the daily traffic (478 ADT) will access the site via New Vine Drive and Blue Spruce Drive South; and approximately 52% of the daily traffic (1,140 ADT) will access the site via Redwood Street and Lupine Drive East. Since the traffic volumes on Blue Spruce Drive North and South are both well below 750 vpd, the applicable setback for all parking areas accessed via Blue Spruce Drive is 40 feet, per LCUASS Figure 19-6. The maximum daily traffic volume on Lupine Drive, at the Redwood Street intersection, is greater than 750 vpd. However, not all traffic entering or exiting the site via this intersection will travel the full length of Lupine Drive. Instead, certain volumes of traffic will enter or exit the street at the various driveways served by Lupine Drive. The number of vehicles entering or exiting the street will typically be proportionate to the resident population served by those driveways and corresponding parking areas. Therefore, the traffic volume in the street will 3715 Shallow Pond Dr., Fort Collins, CO 80528 • Phone (970) 226-0264 • Fax (970) 226-3760 a -,. _.� �� ►,.� =-ter �r.,r�r�.�� a . r/w1�J. wI Will of Sol A m_ OWEN G CONSULTING GROUP, INC. May 15, 2014 Project File #: 11-385 City of Fort Collins Engineering Development Review 281 N. College Ave Fort Collins, CO 80522 Attention: Ms. Sheri Langenberger RE: Aspen Heights Student Housing Interim Detention Basin Outfall — Design Revisions Dear Sheri, In preparation for construction of the interim outfall from the Aspen Heights Detention Basin to the Lake Canal, we undertook a program to better refine the horizontal and vertical locates of the existing utilities in the area where the proposed outfall will cross the Redwood St. alignment and downstream from there to the discharge point at the Lake Canal. The supplementary investigation revealed several conflicts between underground utilities and the outfall pipe, as proposed and approved. Therefore, we have revised the alignment and profile of the outfall to avoid the conflicts and ensure that the required horizontal and vertical separations from existing utilities are maintained. Along with specific revisions to the outfall piping, the revised design also reflects elements of the pending design of Redwood Street, incorporated to ensure that the ultimate design will be compatible with the design for the future completion of Osiander St. in Old Town North, and to accommodate the installation of a box culvert to convey remnant Dry Creek flows beneath Redwood St. and into the historic drainage channel to the Lake Canal. To accomplish these objectives, it was necessary to add one further manhole, and to relocate the three downstream legs of the interim outfall. The overall design concept for the outfall has not changed from that originally proposed and approved. Two sections of the pipe will continue to function as inverted siphons, and will retain water, and a portion of the first pipe run downstream of the detention basin outlet structure will also not completely drain, but the rest of the pipes will drain by gravity. This revised design represents a significant reduction in the length of non -free -draining pipes compared to the previous design (439 ft vs. 646 ft). The proposed revised design for the interim outfall is shown on the attached drawings. I hope that you will find these acceptable and authorize work to proceed on the installation of the piping without delay. If you have questions or comments regarding this submittal, please call me. Thank you for your attention to this matter. Yours truly, Owen i Group, Inc. Larry C. Owen, P.E. Enclosures cc: Glen Schlueter 3715 Shallow Pond Dr., Fort Collins, CO 80528 - Phone (970) 226-0264 Fax (970) 226-3760 Aspen Heights 11 /SV2011 UTILITY COORDINATION ATTENDANCE SHEET Contact name Zq,.,-Ct/ 0f,,,l Company Name /J tJE.✓ Ce.✓sdt�►-ii✓ C�sea v •� Address�r c a men � C.aMC as�.hc� Phone Number/email address c�.rr- 7� l ►-�-�= .i gb5-'mil L G H T q- °Iic�• 7�i1• loloC�� f?d- z.Z41• rolsZ 7-1 r✓e Qq FG ,*7bV, �ylptl'l�n,✓ �� n e� Rov. C:t . Gy as �- "O t Gr Ga � n e � �c o�, cow► �{o�s� Su�tlly� G L/A lLe-,JT Pc, G oZ ( - & 317'-3 �x�QSDIe C'DPa�sn Owen as iar�{ Ms. Sheri Langenberger RE. Aspen Heights Student Housing — Off-street Parking Area Setbacks July 1, 2013 Page 2 of 2 decrease with increasing distance from the access point at Redwood Street. The analysis presented in the attached spreadsheet shows that the daily traffic volume on Lupine Street drops below the 750-vpd threshold at the first pair of driveways west of Redwood Street, and at all locations west of the first two driveways, the street ADT will be less than 750 vpd. Since the driveway volumes are also less than 750 vpd, the required setback distance for the first parking stalls in each of these subsequent parking areas is 40 feet. The only parking areas where the criteria for the 40-foot setback are exceeded are the first pair of driveways west of Redwood Street. Given that these driveways are only two of the 17 driveways in the development, we request that a Modification of Standards be allowed for these two driveways. We trust that you will find the information presented here to be sufficient and acceptable. If you have questions or comments regarding this submittal, please contact me immediately and I will be pleased to discuss any items with you. Thank you for your consideration of this request. Yours truly, Owen Con roup, Inc. Larry C. Owen, P.E. Attachments 4 Z mo 0w >$ p0 , g "a 5 s 01 W V OIJ �1D+L V N W+ W /JOP ag m000)wD SL o 4 R m 001+ N N O OD + G >9 mOA wa g• + V N CI V O !C 9RO15 �� mvv�ma P� �m aW+ oo+ A 4, ooa 1 1�yy Q1 g ONN O AA V NO Or1 ON g m0 0w m m V CC V NNtl1 C >� mvc�c'�aoa s W N O O O+ Amg 4 a y 0 0 0 O' in I I c e w � m J L DJ > I 0 w'r D Z A W W N N i i O 0000000� _D m O a - p a 3 vi N o� 01-4C N N CL o la a v FAO? V A((O W4 v la��ip W 0) O -4W CO Al OD D �v A 2 a m v co 0 m z m G) c v m z 0 'c'^ L' z G) �t R.O.W. I I IPrivate IParking - - Minimum Off Street Parking I Setback Distance to any parking stalls or drive aisle. (See Table below) Back of Sidewalk MINIMUM OFF STREET PARKING SETBACK DISTANCES (FT.) PARKING LOT STREET CLASSIFICATION Volume (AD-0 Local Collector Arterial < 100 ADT 100-750 ADT j > 750 ! ADT <100 20' 40' 40' 59 50' 1 i 100-750 29 40 50' 50' 75' >750 NA 50' 50' 60' 100' MINIMUM OFF STREET PARKING SETBACK DISTANCE LARIMER COUNTY DESIGN REVISION NO: I FIGURE URBAN AREA FIGURE i%ATLW. n03 fin+ ono In e OWE N (; CONSULTING GROUP, INC. July 1, 2013 Project File #: 11-385 City of Fort Collins Engineering Development Review 281 N. College Ave Fort Collins, CO 80522 Attention: Ms. Sheri Langenberger RE: Aspen Heights Student Housing Utility Crossings — Depth of Cover Dear Sheri, There are two locations where we believe that it is not practical to provide three feet of cover over utility pipes crossing beneath public streets. Accordingly, we are hereby requesting that a Modification of Standards be allowed at each of these two locations. Details of the subject crossings are presented below in support of our request. The first location is at the crossing beneath Lupine Drive of the culvert pipes in the main north- ~ ,ram south drainage channel. The design presented in the FDP drawings for the Aspen Heights project provides 2.0 feet of cover at the street centerline. The attached figure shows a cross-section ' 0� through the channel, the culverts and the underlying NECCO piping at the crossing point. The elevation and gradient of the main drainage channel are governed by 1) the invert elevations of the existing culverts beneath Conifer Street, at the upstream end of the channel, 2) the design of the NECCO detention basin, at the downstream end of the channel, and 3) the design of the underlying NECCO storm drain piping, throughout the length of the channel. The size of the culverts beneath Lupine Drive is driven by the hydraulic capacity required to convey the ultimate design flow in the channel, per the NECCO hydrologic analysis and the drainage analysis for the Aspen Heights site. In order to convey the ultimate 100-year design flow in the channel (159.4 cfs) beneath Lupine Drive, without overtopping the street, four 24" x 38" HERCP culverts are required. In the near term, prior to completion of the NECCO system upstream and downstream of the Aspen Heights site, the north -south channel through the site will also carry flows that will ultimately be conveyed in the NECCO storm drain beneath the channel. Thus, the near term peak flow in the channel will be somewhat greater than the ultimate 100-year flow. The near -term peak flow in the channel is estimated to be 239.7 cfs. If this 100-yr flow is experienced, prior to the completion of the NECCO system, a portion of the flow in the channel will overtop the street. Analysis shows that the depth of overtopping will be slightly less than 6 inches. However, in order for the overtopping to occur at the channel crossing, and for the overtopping flow to reenter the channel downstream of the street, the profile of Lupine Drive must include a low point coincident with the channel crossing. That is the condition presented in the current design. The profile of Lupine Drive is mandated by the overall grading of the development site. To raise the elevation of Lupine Drive at the channel crossing would necessitate raising grades throughout a substantial area of the site in order for the site to drain efficiently. Because there is very little relief throughout the site, overall, the street profile grades are also relatively flat, both east and west of the channel crossing. Raising the elevation of the street by one foot at the channel crossing would reduce the profile grade west of the crossing to approximately 0.51 % and would reverse the gradient 3715 Shallow Pond Dr., Fort Collins, CO 80528 • Phone (970) 226-0264 Fax (970) 226-3760 Ms. Sheri Langenberlger RE., Aspen Heights Student Housing — Request for Modification of Standards July 1, 2013 Page 2 of 2 east of the crossing, such that the street gradient would fall continuously from Blue Spruce Drive to a point well east of the channel crossing. This would substantially alter the site drainage regime, as well as adding substantially to the amount of fill required to grade the site. Thus, we are requesting that the proposed design at the Lupine Drive crossing be approved. To minimize the risk of reflective cracking of the pavement in the vicinity of the channel crossing, we propose, as part of this request, to replace the asphalt pavement, throughout the full width of the street and the length of the channel crossing, with a reinforced concrete slab pavement. Details of the slab design, as well as the backfill around the culverts supporting the slab, will be finalized in conjunction with the final design of the pavement section(s) throughout the balance of the site. The second location for which a Modification of Standards is requested is the crossing of the detention basin interim outfall piping beneath Redwood Street. As currently designed, the cover over the pipe is 2.22 feet at the west flow line of the street, 3.07 feet at the street center line, and 2.78 feet at the east flow line. The elevation of the outfall pipe has been lowered as much as possible, and use of HERCP pipe has been specified to reduce the vertical dimension of the pipe. Further lowering of the pipe is prevented by the existing sanitary sewer main in Redwood St. The sewer main is laid at minimum gradient, so it cannot be lowered. Consideration was given to lowering the profile of the outfall such that it would pass beneath the sanitary sewer main, however, to do so would result in this section of the outfall being at an elevation more than nine feet below grade and more than five feet below the invert of the Lake Canal at the discharge point. As we have discussed previously, the shallow invert elevation of the Lake Canal (4952.2 ft), will result in all outfall piping set below that elevation remaining continuously surcharged, or partially inundated, until such time as the permanent NECCO outfall is installed. By installing this section of the outfall at the elevation shown in the current design, none of the interim outfall piping, with the exception of the section crossing New Vine Drive, will remain completely surcharged. Several runs of pipe near the downstream end will remain partially inundated, but none completely. A backflow prevention flap at the outfall will prevent water from the Lake Canal entering the outfall piping. A request for a Modification of Standards is requested for this location. Given the limited magnitude of the reduced cover over the outfall pipe, no other mitigating design revisions are proposed for this location. I trust that you will find the information presented here to be sufficient and acceptable. If you have further questions or comments regarding these requests, please contact me immediately to discuss them. Thank you for your consideration. Yours truly, Owen Cons roup, Inc. Larry C. Owen, P.E. Attachments • 1: TJVT.JV 4963.53 4964.99 I11 l 1 1 PT. 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