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Home My WebLink About112 W Magnolia Street Parking Lot - FDP - FDP180017 - Stormwater Related Documents SUBMITTAL DOCUMENTS - ROUND 1 - 01/12/2018 January 12, 2018 Mrs. Heidi Hansen City of Fort Collins Engineering Department 700 Wood Street Fort Collins, Colorado 80521 RE: Supplemental Memorandum: No-Rise Certification to Floodplain Use Permit 112 West Magnolia Street, Fort Collins, Colorado 80525 CES Project No. 6300-01 This memorandum serves to supplement and further describe the work proposed with the Floodplain Use Permit for Wells Fargo. The project site is located in the Old Town Basin 100-yr floodplain, a City of Fort Collins regulatory floodplain. Since improvements area proposed within the High Risk Flood Fringe, City Floodway, and Moderate Risk Floodplain, all work contained therein is subject to Chapter 10 of the City of Fort Collins Municipal Code Flood Prevention and Protection. The subject property itself is located within a Moderate Risk Zone and High Risk Flood Fringe, as defined -yr floodplain for the Old Town Basin. Additionally, the adjacent public right-of-way for Magnolia Street and College Avenue both contain High Risk Floodway and Flood Fringe areas. Appendix A illustrates the existing Flood Hazard Areas affecting 112 West Magnolia Street. The High Risk Flood Fringe boundary line starts at the back edge of the sidewalk along Magnolia Street and covers the south half of the site. The Moderate Risk Floodplain covers the north half of the site. The proposed Wells Fargo parking lot improvements do not require hydraulic analysis to show no-rise because there are no changes to the Old Town Basin HEC-RAS model. The HEC-RAS cross-section is located at an existing access to the parking lot, but is modeled with an ineffective area past the right-of- way. The proposed work for the site will abandon this existing access, and be replaced with curb and gutter. Since the existing Old Town Basin Model represents the proposed conditions, the City of Fort Collins does not require an analysis to justify no-rise. Other improvements in addition to the parking lot to be constructed within the 100-yr High Risk Flood Fringe include paving, curbs, sidewalk, utilities, and landscaping. These standard site work items are allowed within the 100-yr Old Town Basin High Risk Flood Fringe without the need for special provisions or additional documentation. See the appendix for the location of the HEC-RAS cross-section and the section view of the cross-section However, a portion of the proposed improvements (curb & gutter and asphalt patch), also reside within the 100-yr High Risk Floodway. Per Chapter 10 of the Municipal Code, all work within the floodway must be accompanied by No-Rise Certification. The High Risk Floodway follows the back of sidewalk past the centerline of Magnolia Street and College Avenue. This means that a portion of the driveway, sidewalk, and sidewalk chase will occur within the floodway. Curb and gutter will be replaced at existing grade. COFFEY ENGINEERING & SURVEYING (970) 622-2095 4045 ST CLOUD DRIVE LOVELAND, COLORADO Page 2 The primary technical justification used to support the No Rise Certification is the existing and as-built survey information. Detailed existing survey data was gathered by King Surveying. A copy of the existing conditions survey can be found in the appendix. The new curb, gutter, and sidewalk elements to be constructed within the High Risk Floodplain shall not exceed the existing survey elevations when rounded to the tenth of a foot. The permeable pavers underdrain storm system connection will also occur in the floodway. All hardscape within the High Risk Floodway will be placed at or below existing grade, and will be validated by an as-built survey. There are two existing driveways along Magnolia Street and one existing driveway along College Avenue that will be abandoned within the floodway to eliminate vehicular access to the site at these locations. A new driveway cut and ADA access ramps will be installed on Magnolia Street to replace the abandoned accesses. Filling in the old driveways and cutting in the new driveway should not impact the floodplain since the existing driveways are represented with ineffective flow areas behind the right-of-way in the hydraulic model. Existing and as-built survey points shall confirm that the elevation along the curb and gutter is maintained. Therefore, the net effect results in no change to the floodway or flood fringe boundaries and does not alter the Base Flood Elevations. The purpose of Chapter 10 of the City of Fort Collins Municipal Code is to promote the public health, safety and general welfare and to minimize public and private losses due to flood conditions in flood hazard areas, which is accomplished by the governing methods and provisions contained therein. The specific sections of Chapter 10 applicable to this particular Floodplain Use Permit are: Sec. 10-27. Floodplain Use Permit A floodplain use permit shall be obtained before any construction or development within the flood fringe and floodway pursuant to Chapter 10. The sitework proposed herein qualifies as development by Sec. 10-16. Sec. 10-45. Floodway Evaluations the proposed sitework within the floodway will result in no increase in base flood elevations. This document accompanies the requisite No Rise Certification. Existing survey information has been provided for the sitework area within the floodway. As-built survey information shall be provided after the sidewalk, driveway, and parking lot improvements have been constructed to ensure no change in the floodway boundary or increase in base flood elevations. Sec. 10-111. Specific Standards for Nonstructural Development in Flood Fringe There are two existing driveways along Magnolia Street and one existing driveway along College avenue that will be abandoned within the floodway to eliminate vehicular access to the site at these locations. A new driveway cut and ADA access ramps will be installed on Magnolia Street to replace the abandoned accesses. These non- structural improvements are allowed in the floodway contingent upon the No Rise Certification reference in Sec. 10-45 above. This memorandum serves as documentation of the sitework proposed within the 100-yr High Risk Flood Fringe and Floodway of the Old Town Basin floodplain. Improvements will occur with the Development Construction Permit for Wells Fargo. The applicable sections of Chapter 10 of the City of Fort Collins Municipal Code are reference above. A post-construction certification shall also be supplied to ensure that the construction activities covered under this permit were consistent with the governing plans and requirements. As-built field survey information shall be supplied in support of the post-construction certification. Page 3 Please feel free to contact me if you have any questions or require additional information. Sincerely, COFFEY ENGINEERING & SURVEYING Reviewed by, Ramsey Pickard, EI Cody Geisendorfer, PE, CEM Civil Designer I Principal Engineer Attachments Appendix A -Floodplain Use Permit -Certification of No-Rise -City of Fort Collins Flood Risk Map -Cross Section Exhibit/Site Plan -Cross-Section Profile -Existing Survey completed by King Surveyors ENGINEERING DEPARTMENT Post Office Box 1190 Fort Collins, Colorado 80522-1190 (970) 498-5700 FAX (970) 498-7986 CERTIFICATION OF NO-RISE This is to certify that I am a duly qualified registered professional engineer licensed to practice in the State of Colorado. It isto further certify that the attached technical data supports the fact that proposedor as-built (Name of Development) activities in the floodway willnot create an adverse rise or drop inthe 100-year flood elevations, change the watercourse location, orimpact the 100-year flood elevations, floodway elevations, or floodway widthson (Name of Stream) in accordance with Section 4.2.2 of the Larimer County Land Use Code atpublishedcross-sections in the Flood Insurance Study for Larimer County revised on February 6, 2013 and will not createan adverse rise or drop in the 100-year flood elevations, change the watercourse location, or impact the 100- year flood elevations, floodway elevations, or floodway widths at unpublished cross-section in the vicinity of the proposed development. 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Qsjoufe;!1403603127 gmppeqmbjot/!Mpdbm!esbjobhf!qspcmfnt!nbz!tujmm!fyjtu/ FORT COLLINS CO, 80525 112 WEST MAGNOLIA STREET WELLS FARGO PARKING LOT IMPROVEMENTS 20' 10' N SCALE: 1" = 10' 0 CALL 811 WWW.UNCC.ORG (OR 1-800-922-1987) BEFORE YOU DIG UTILITY NOTIFICATION UTILITY PLAN APPROVAL CENTER OF COLORADO (UNCC) THREE (3) BUSINESS DAYS FOR BURIED UTILITY INFORMATION R CITY OF FORT COLLINS, COLORADO MEASURED AS THE FLOWLINE UNLESSOTHERWISE NOTED NOTE:1.) ALL LINE AND CURVE TAGS ARE EXISTING 5' SW 4' SCREEN WALL 5.0' 6.0' 11.5' INV: 94.06' UNDERDRAIN 8 PROPOSED BIKE RACK 8.0'8.0' 8.0' 6.5' UNDERDRAININV: 93.79' 6.0' 24.0' PROPOSED2' U-CHANNEL 7 3.00' 25.0' 30.9' INV: 93.75' UNDERDRAIN UNDERDRAININV: 93.58' 'HEC-RAS CROSS-SECTION RIVER STATION 2068 0 0 . 24.0' 6 DELTA 090.0000090.0000090.0000090.0000090.0000090.0000090.0000090.0000090.0000 2.5002.5002.5002.5002.500 1.5001.5001.5001.500 RADIUS 9.0' TYP MAGNOLIA STREET 3.9273.9272.3563.9272.3563.9272.3563.9272.356 INV: 93.51' LENGTH UNDERDRAIN CURVE TABLE C11C12C13C14C15C16C17C18C19 11.5' PLANTING AREA CURVE # 64.2' 5.0' 19.0' TYP UNDERDRAININV: 93.33' DELTA 090.0000090.0000090.0062090.0000090.0000090.0000093.6316091.0163090.0000090.0000 5.5' 7.381 2.5001.5001.5001.5001.5001.5007.5451.5001.500 RADIUS 2.3562.3562.3562.3562.3562.3562.356 3.927 12.32911.725 LENGTH CURVE TABLE 24.0'24.0' C1 C2C3C4C5C6C7C8C9 C10 CURVE # ACCESS RAMP WITH TRUNCATED DOMES (TYP) INV: 93.13' 3.186.963.356.11 UNDER DRAIN 14.0223.0715.5046.0015.5014.5032.0034.0032.0034.0012.2522.54 DISTANCE PROPOSED4' MANHOLE 5 UNDERDRAININV: 93.60' 5.0' 25.0 BEARING LINE TABLE L21L31 L17L18L19L20L22L23L24L25L26L27L28L29L30L32 LINE # UNDERDRAININV: 93.77' EXISTING AVENUE 2.003.503.509.003.503.509.00 62.5017.5025.0014.5016.5025.0016.5017.50 161.53 DISTANCE BEARING LINE TABLE L1 L2L3L4L5L6L7L8L9 L11 L10L12L13L14L15L16 LINE # Fmfwbujpo!)gu*