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Home My WebLink AboutMULBERRY CONNECTION - FDP200030 - DOCUMENT MARKUPS - ROUND 3 - DRAINAGE REPORTkimley-horn.com 4582 South Ulster Street, Suite 1500, Denver, CO 80237 303 228 2300 DRAINAGE REPORT COVER LETTER To: City of Fort Collins Matt Simpson, P.E., CFM Development Review Engineer From:Dan Skeehan, P.E. Kimley-Horn and Associates, Inc Date:January 21, 2021 Subject:Mulberry Connection, PDP190015 Drainage Report Cover Letter Kimley-Horn and Associates, Inc. (Kimley-Horn) is submitting this Drainage Report Cover Letter for the above referenced project. The purpose of this letter is to serve as an outline for the proposed development and associated drainage. PROJECT DESCRIPTION The proposed Mulberry Connection Project is located within the Northeast Quarter of Section 9, Township 7 North, Range 68 West of the Sixth Principal Meridian, City of Fort Collins, County of Larimer, Colorado. A vicinity map is provided below. 8 drainage swale south of the intersection via a 2-foot curb cut. Water continues flowing south via an existing grass swale that is proposed to be modified with the adjacent roadway improvements. The proposed improvements to I-25 Frontage Road increase the impervious area from 0.50 acres to 0.55 acres, which results in an increase in the 100-year flow rate from 5.28 CFS to 7.21 CFS, an increase of 1.93 CFS. The proposed 100-year flows from sub-basins O4 and OS1 were combined and the hydraulic capacity of the proposed grass swale evaluated. The Bentley FlowMaster calculations are included in Appendix D and indicate that the grass swale has capacity for the increased flows in the proposed condition. Water quality treatment nor detention will be provided for this sub-basin on the proposed site. Additionally, this basin is not included as a part of the total Site improvement area, as proposed off-site improvements will improve existing conditions and maintain historic drainage patterns. Sub-basin OS2 Sub-basin OS2 is 0.55 acres and consists of a portion of Redman Drive and offsite landscape area. Runoff within this sub-basin will surface flow to proposed curb and gutter adjacent to the Site and the existing drainage ditch on the north side of Redman Drive. Water quality treatment nor detention will be provided for this sub-basin. Additionally, this basin is not included as a part of the total Site improvement area, as proposed off-site improvements will improve existing conditions and maintain historic drainage patterns. 16 2.4 CFS and 9.6 CFS of runoff is generated from sub-basin OS-1 in the 2-year and 100-year storm events, respectively. On-site sub-basin O4 also flows to the I-25 Frontage Road. The total flows in the roadway are 2.5 CFS and 9.8 CFS in the 2-year and 100-year storm events, respectively. The UD-Inlet street capacity analysis indicates that in the 2-year storm event flows will spread 8.5 feet from the flowline into the roadway, which will occupy 0.5-feet into the travel lane. This spread results in 5-inches of ponding at the curb flowline. In the 100-year storm event flows will spread 16-feet from the flowline into the roadway, which will occupy 8-feet of the travel lane. This spread results in 6-inches of ponding at the curb flowline. VARIANCE REQUESTS A variance is requested to allow the inflow infiltration basin within the detention pond. A separate variance request will be submitted. EROSION CONTROL A separate Erosion Control Report will be provided in addition to this Final Drainage Report. CONCLUSIONS COMPLIANCE WITH STANDARDS The Mulberry Connection project is in compliance with City of Fort Collins criteria for storm drainage design. The “Fort Collins Stormwater Criteria Manual, December 2018 Edition,” and the Urban Drainage Flood Control District “Urban Storm Drainage Criteria Manual Volumes 1, 2, and 3 have been utilized for reference. SUMMARY OF CONCEPT The proposed drainage concept is to surface flow runoff from impervious areas to pervious area to the extent practicable. Two rain gardens and one underground facility are proposed to treat the WQCV from as much of the Site as possible. A detention pond is proposed to detain the on-site 100-year runoff volume to the 2-year historic on-site flow. Downstream impacts due to the development of this Site are not anticipated. REFERENCES Fort Collins Stormwater Criteria Manual, December 2018 Edition, City of Fort Collins. Urban Storm Drainage Criteria Manual, Volume 1-3, Urban Drainage and Flood Control District, Denver, CO; January 2016, with latest revisions. APPENDICES A. NRCS Data and FEMA Map B. Existing and Proposed Drainage Map C. Hydrologic Calculations D. Hydraulic Calculations E. Reference Materials Worksheet for OFFSITE CURB CUT Project Description Manning FormulaFriction Method DischargeSolve For Input Data 0.013Roughness Coefficient ft/ft0.050Channel Slope in6.0Normal Depth ft2.00Bottom Width Results cfs12.29Discharge ft²1.0Flow Area ft3.0Wetted Perimeter in4.0Hydraulic Radius ft2.00Top Width in12.7Critical Depth ft/ft0.006Critical Slope ft/s12.29Velocity ft2.35Velocity Head ft2.85Specific Energy 3.064Froude Number SupercriticalFlow Type GVF Input Data in0.0Downstream Depth ft0.0Length 0Number Of Steps GVF Output Data in0.0Upstream Depth N/AProfile Description ft0.00Profile Headloss ft/sInfinityDownstream Velocity ft/sInfinityUpstream Velocity in6.0Normal Depth in12.7Critical Depth ft/ft0.050Channel Slope ft/ft0.006Critical Slope Page 1 of 127 Siemon Company Drive Suite 200 W Watertown, CT 06795 USA +1-203-755-1666 1/19/2021 FlowMaster [10.03.00.03] Bentley Systems, Inc. Haestad Methods Solution CenterMulberry Connection.fm8 Project: Inlet ID: Gutter Geometry (Enter data in the blue cells) Maximum Allowable Width for Spread Behind Curb TBACK =0.0 ft Side Slope Behind Curb (leave blank for no conveyance credit behind curb)SBACK =0.000 ft/ft Manning's Roughness Behind Curb (typically between 0.012 and 0.020)nBACK =0.013 Height of Curb at Gutter Flow Line HCURB =6.00 inches Distance from Curb Face to Street Crown TCROWN =48.0 ft Gutter Width W =2.00 ft Street Transverse Slope SX =0.020 ft/ft Gutter Cross Slope (typically 2 inches over 24 inches or 0.083 ft/ft)SW =0.083 ft/ft Street Longitudinal Slope - Enter 0 for sump condition SO =0.015 ft/ft Manning's Roughness for Street Section (typically between 0.012 and 0.020)nSTREET =0.016 Minor Storm Major Storm Max. Allowable Spread for Minor & Major Storm TMAX =8.5 16.0 ft Max. Allowable Depth at Gutter Flowline for Minor & Major Storm dMAX =5.0 6.0 inches Allow Flow Depth at Street Crown (leave blank for no)check = yes Maximum Capacity for 1/2 Street based On Allowable Spread Minor Storm Major Storm Water Depth without Gutter Depression (Eq. ST-2)y =2.04 3.84 inches Vertical Depth between Gutter Lip and Gutter Flowline (usually 2")dC =2.0 2.0 inches Gutter Depression (dC - (W * Sx * 12))a =1.51 1.51 inches Water Depth at Gutter Flowline d =3.55 5.35 inches Allowable Spread for Discharge outside the Gutter Section W (T - W)TX =6.5 14.0 ft Gutter Flow to Design Flow Ratio by FHWA HEC-22 method (Eq. ST-7)EO =0.658 0.372 Discharge outside the Gutter Section W, carried in Section TX QX =0.9 7.2 cfs Discharge within the Gutter Section W (QT - QX)QW =1.8 4.3 cfs Discharge Behind the Curb (e.g., sidewalk, driveways, & lawns)QBACK =0.0 0.0 cfs Maximum Flow Based On Allowable Spread QT =2.7 11.5 cfs Flow Velocity within the Gutter Section V =4.2 5.9 fps V*d Product: Flow Velocity times Gutter Flowline Depth V*d =1.2 2.6 Maximum Capacity for 1/2 Street based on Allowable Depth Minor Storm Major Storm Theoretical Water Spread TTH =14.5 18.7 ft Theoretical Spread for Discharge outside the Gutter Section W (T - W)TX TH =12.5 16.7 ft Gutter Flow to Design Flow Ratio by FHWA HEC-22 method (Eq. ST-7)EO =0.409 0.318 Theoretical Discharge outside the Gutter Section W, carried in Section TX TH QX TH =5.4 11.5 cfs Actual Discharge outside the Gutter Section W, (limited by distance TCROWN)QX =5.4 11.5 cfs Discharge within the Gutter Section W (Qd - QX)QW =3.7 5.4 cfs Discharge Behind the Curb (e.g., sidewalk, driveways, & lawns)QBACK =0.0 0.0 cfs Total Discharge for Major & Minor Storm (Pre-Safety Factor)Q =9.1 16.9 cfs Average Flow Velocity Within the Gutter Section V =5.6 6.4 fps V*d Product: Flow Velocity Times Gutter Flowline Depth V*d =2.3 3.2 Slope-Based Depth Safety Reduction Factor for Major & Minor (d > 6") Storm R =1.00 1.00 Max Flow Based on Allowable Depth (Safety Factor Applied)Qd =9.1 16.9 cfs Resultant Flow Depth at Gutter Flowline (Safety Factor Applied)d =5.00 6.00 inches Resultant Flow Depth at Street Crown (Safety Factor Applied)dCROWN =0.00 0.00 inches MINOR STORM Allowable Capacity is based on Spread Criterion Minor Storm Major Storm MAJOR STORM Allowable Capacity is based on Spread Criterion Qallow =2.7 11.5 cfs Version 4.06 Released August 2018 ALLOWABLE CAPACITY FOR ONE-HALF OF STREET (Minor & Major Storm) (Based on Regulated Criteria for Maximum Allowable Flow Depth and Spread) Enter Your Project Name Here I-25 Fornatge Rd (OS1, O4) Minor storm max. allowable capacity GOOD - greater than the design flow given on sheet 'Inlet Management' Major storm max. allowable capacity GOOD - greater than the design flow given on sheet 'Inlet Management' UD-Inlet_v4.06 (7).xlsm, I-25 Fornatge Rd (OS1, O4)1/19/2021, 4:30 PM