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Home My WebLink AboutASPEN HEIGHTS STUDENT HOUSING - FDP - FDP130010 - SUBMITTAL DOCUMENTS - ROUND 2 - UTILITY PLANS~ B IOWEN GROUP, CONSULTING 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 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 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 1 OO-year flow. The near-term peak flow in the channel is estimated to be 239.7 cfs. If this 1 OO-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 Langenberger RE: Aspen Heights Student Housing - Request for Modification of Standards July 1, 2013 Page 20f2 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. Larry C. Owen , P.E. Attachments LOW PT STA: 15+18.73 --++--_---- +LOW 1PVI PT STA: ELEV: 15+4963.06.99_16 -++-1----_.-.-.+.-.--_----+--i_---_---i-+---_ _f___+_ _ 4980 -+-------:-+. PVI ELEV: 4963.07 --,---+-----+---+---~-~ §;O)~ +::: ~ ~. I') ··LVC: K: 57.70.37 00 g ~I') ~ +~ ~ co ~ iii LJ --I----r-11I .• ... ~ • It) .... .:J u: <i l~ LIS I 4970 Z HIll) a ~ 1&.1 STAt ' 15+ 18. 73 bI ROAD CENTER I OF -I--- it a.. V .........EL.E\f. 4963.1 P LI I LINE PROFILE ~ . I I -r- T--_ I -nA: ¥ 7 T - 1 ~ ~~ -= "\. W !- ~ 1"\ '\. , / / ~ ~ DEPTH OF COVER @ -l N I '\.. \ I Y / " ROAD CENTER LINE W v I 66" DIA. RCP NECCO STORM MAIN II- 4950 o o • o It) o .+ ... .o co + ... It) .co + ... HORIZ: SCALES: 1" = 30' .... . A I II Nll ~I \ 7 ;:::I:' - I I 4960 I .~ I') ..... LJ. )1 11 11 U j(~~.c: 15+80.21 -1 -I v: 4963.37""1 -~ - ~ STORMWATER CHANNEL --1-1----- 20' 4:1 BOTTOM SIDE SLOPES WIDTH WI v I __ Ir\ \ I r ) I') m It) 0Cl It) I"") I') m 0 -.;t -.;t- It) m .) It) m I') I' ~ N I') I"") It) . • • m . N • m . ...• . I"") N • N • . ~ 0 0 . I') -.;t- I') -.;t- I') I"") I') I') • -.;t- -.;t- I')• l I') -.;t- I') m -.;t- .) ) co m CD co m CD co m CD co m CD co m L() 0) co m CD co m CD co m CD I ~ -.;t ~ -.;t ~ -.;t- ~ -.;t ~ -.;t ~ -.;t ~ -.;t ~ -.;t VERT: 1" = 6' It) co I') co • ~ iYlILY£~ - dr/l?n~ (j~),'T/a"/ 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 cfs Inlet Control HW Elev. 4,962.44 ft Tailwater Elevation 4,960.54 ft Outlet Control HW Elev. 4,962.81 ft Control Type Outlet Control Grades Upstream Invert 4,959.18 ft Downstream Invert 4,958.80 ft Length 124.00 ft Constructed Slope 0.003065 tuft Hydraulic Profile Profile CompositeM2PressureProfile Depth, Downstream 1.74 ft Slope Type Mild Normal Depth N/A ft Flow Regime Subcritical Critical Depth 1.74 ft Velocity Downstream 8.44 tus Critical Slope 0.007616 tuft 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. 4,962.81 ft Upstream Velocity Head 0.95 ft Ke 0.20 Entrance Loss 0.19 ft Inlet Control Properties Inlet Control HW Elev. 4,962.44 ft Flow Control Submerged Groo+alet1~i1h headwall (horizontal ellipse) Area Full 20.4 ft2 K 0.00180 HDS 5 Chart 29 M 2.50000 HDS 5 Scale 2 C 0.02920 Equation Form y 0.74000 Project Engineer: LARRYOWEN8BBF\Administrator main channel culverts under lupine - revised 12-02... CAiHE Academic SiteExton CulvertMaster v3.3 [03.03.00.04J C~t/Ee7S .:z;;,t£el# ('~,JA rJ/CJ,J Culvert Calculator Report Aspen Heights - Lupine Street Culverts Solve For: Headwater Elevation Culvert Summary Allowable HW Elevation 4,964.00 ft Headwater Depth/Height 3.30 Computed Headwater Elev, 4,965.77 ft Discharge 239.67 cfs Inlet Control HW Elev. 4,964.93 ft Tailwater Elevation 4,960.98 ft Outlet Control HW Elev. 4,965.77 ft Control Type Outlet Control Grades Upstream Invert 4,959.18 ft Downstream Invert 4,958.80 ft Length 124.00 ft Constructed Slope 0.003065 ftlft Hydraulic Profile Profile PressureProfile Depth, Downstream 2.18 ft Slope Type N/A Normal Depth N/A ft Flow Regime N/A Critical Depth 1.93 ft Velocity Downstream 11 .75 ftls Critical Slope 0.017022 ftlft 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. 4,965.77 ft Upstream Velocity Head 2.15 ft Ke 0.20 Entrance Loss 0.43 ft Inlet Control Properties Inlet Control HW Elev. 4,964.93 ft Flow Control Submerged GhdeveJlDll!l projecting (horizontal ellipse) Area Full 20.4 ft2 K 0.00450 HDS 5 Chart 29 M 2.00000 HDS 5 Scale 3 C 0.03170 Equation Form Y 0.69000 Project Engineer: LARRYOWEN8BBF\Administrator main channel culverts under lupine - revised 12-02... CAiHE Academic SiteExton CulvertMaster v3.3 [03.03.00.04] Culvert Calculator Report Aspen Heights - Lupine Street Culverts Solve For: Discharge Culvert Summary Allowable HW Elevation 4,964.00 ft Headwater Depth/Height 2.41 Computed Headwater Elev, 4,964.00 ft Discharge 190.28 cfs Inlet Control HW Elev. 4,963.20 ft Tailwater Elevation 4,960.98 ft Outlet Control HW Elev. 4,964.00 ft Control Type Outlet Control Grades Upstream Invert 4,959.18 ft Length 124.00 ft Hydraulic Profile Profile PressureProfile Slope Type N/A Flow Regime N/A Velocity Downstream 9.33 ftls Downstream Invert Constructed Slope Depth, Downstream Normal Depth Critical Depth Critical Slope 4,958.80 ft 0.003065 ftlft 2.18 ft N/A ft 1.84 ft 0.010555 ftlft 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 Grooilllelnllypah headwall (horizontal ellipse) Area Full 20.4 ft2 K 0.00180 HDS 5 Chart 29 M 2.50000 HDS 5 Scale 2 C 0.02920 Equation Form Y 0.74000 Project Engineer: LARRYOWEN8BBF\Administrator 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 ft3/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 fils Wetted Perimeter 55.89 ft Top Width 55.00 ft Bentley Systems, Inc. Haestad Methods SolBBoH~Master V8i (SELECTseries 1) [08.11 .01 .03J 6/26/2013 12:43:20 PM 27 Siemons Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 Page 1 of 1 Alignment - (STORM 500) - (22) STA: -0+50.00 THRU 1+50.00 STATION -0+50 0+00 1+00 1+50 JTI r rrI ~ ::I o z 4970 L L 4970 MANHOlE - (505) STORM MANHOLE TOP = 4956.75:1: IE IE IN IN = = 4952.4952.75 75 ' \ IE OUT - 4952.09 t 1 -f- PIPE - (505) \ 60 - f- o 90 0.LF 20" OF GRADE. 19·X30· ERCP h \ \ 49 4960 \ --- ----- +----r- -t \ -" -- - z 0 '" r 0 , F N " M N N ~ N w III ~ 1 W 49 B V .... H I CROSSING ALTERNATE PROFILE PIPE I 50 4950 MANHOLE - (502) /' 1' Mi STORM MANHOlE TOP = 4957.25:1: I PIPE - (506) IE IN = 4951.41 IE IN = 4951.90 0 0.50" GRADE. IE OUT = 4951.41 I PIPE - (316) OITCH INLET (506) 15· PVC - STA 1+30.08 SAN. SEWER TYPE C DITCH INLET RIM = 4954.64:1: IE OUT = 4952.93 40 I 49 I I 4940 , -0+50 0+00 1+00 1+50 STATION