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Home My WebLink AboutMASON STREET SUSTAINABLE DEVELOPMENT - PDP - PDP130038 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT (3)1501 Academy Ct. Ste. 203 Fort Collins, Colorado 80524 (970) 530-4044 Preliminary Drainage Summary S 401 South Mason Street FortCollins Fort Collins, , CO Prepared for: Coin Street Mason, LLC. 5425 Tradewind Drive Windsor, CO 80528 October 9, 2013 Drainage Summary 401 South Mason Street Fort Collins, CO 1 U13008-DrainageSummary-Preliminary.doc October 9, 2013 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: 401 South Mason Street Fort Collins, Colorado Project Number: U13008 Dear Staff: United Civil Design Group, LLC. is pleased to submit this Preliminary Drainage Summary for the 401 South Mason Street site in Fort Collins, Colorado. In general, this summary serves to document the stormwater impacts associated with the proposed 401 South Mason Street project. Site Location and Project Description The development site (referred herein as ”the site”) is located at 401 South Mason Street in the City of Fort Collins, Colorado. The site consists of approximately 2,830 square-feet (sf) and is bounded by Magnolia Street on the north, Mason Street on the East, an existing restaurant on the south, and a residential property to the west. See the attached Drainage Exhibit for additional information. The planned development for the site will consist of the following: • The removal of the existing one-story building and parking areas on the site. • The construction of multi-story, mixed-use building with a proposed footprint of approximately 2,830 sf. • The construction of utilities to support the proposed building including sanitary, water and storm drainage. • The construction of right-of-way improvements including public sidewalk, drive approach and landscaping. Existing Conditions Hydrology The site (Basin A1), which is located within the Old Town Basin, currently consists of an existing one-story building, parking area, and a small landscape area with an existing percent-imperviousness of approximately 88%. Storm runoff from the site currently drains towards Magnolia and Mason Streets where runoff is intercepted by existing Drainage Summary 401 South Mason Street Fort Collins, CO 2 U13008-DrainageSummary-Preliminary.doc storm sewer inlets and piping located within Mason Street. Refer to Appendix A for additional information. Floodplain The site is located within the City-regulatory Old Town Basin 100-year floodway, flood fringe, and moderate risk flood fringe. Refer to the attached Drainage Exhibit for additional information. Developed Conditions Hydrology The developed site of 2,830 sf will be entirely covered by the proposed building footprint. The rooftop is currently being proposed to provide approximately 970 sf of green roof which results in a proposed percent-imperviousness for the site (Basin A1) of approximately 60%. Existing drainage patterns are being preserved with the proposed development and water from the site will be directed from the rooftop to the existing storm sewer system located with Mason Street. Refer to Appendix A for additional information. Floodplain The site is located within the City-regulatory Old Town Basin 100-year floodway, flood fringe, and moderate risk flood fringe. The following requirements shall be met regarding the construction of the proposed mixed-use building: • The development team is currently proposing to flood proof the proposed building in lieu of raising the finished floor 18-inches above the Base Flood Elevation (BFE). Refer to the architectural plans for additional information regarding the building flood proof design. All flood proofing measures shall adhere to Section 10-38 of the City Code and the requirements set forth within the City’s “Floodproofing Guidelines”. A Flood Proofing Certificate will be required prior to the issuance of a certificate of occupancy. • All development within the city regulatory floodway must be preceded by an approved floodplain use permit and $25 fee. • All development within the city regulatory floodway must be preceded by an approved no-rise certification followed by re-certification of no-rise in the as- built condition. Detention Requirements Per communication with City personnel, the site has historically paid fees for 100% imperviousness. As the existing site currently has an approximate imperviousness of approximately 88%, City personnel have indicated that the development may request a variance to the detention requirement for the site. This variance request is being Drainage Summary 401 South Mason Street Fort Collins, CO 3 U13008-DrainageSummary-Preliminary.doc requested with this PDP Submittal and the site currently does not provide onsite detention. Water Quality Requirements The site is located within the Udall Natural Area which provides water quality for the site; and therefore, additional water quality is not required. However, the development is currently proposing to provide approximately 970 sf of green roof which will provide additional water quality for the site. Low Impact Development (LID) Requirements The developed site (Basin A1) of 2,830 sf will be entirely covered by the proposed building footprint. Therefore, with no paving being provided, the site is not providing pervious paved areas. In order to meet LID requirements, the rooftop of the building is being proposed with approximately 970 sf of green roof resulting in a lower percent- imperviousness and less overall runoff from the site compared to existing conditions. Details of the green roof will be provided with subsequent submittals; however, for this submittal calculations have been provided for the green roof assuming characteristics of a rain garden with an underdrain system. Refer to Appendix B for rain garden calculations. Conclusions In conclusion, the drainage system proposed within this drainage summary provides adequate conveyance of the developed stormwater runoff from the proposed development to existing discharge locations and drainage systems. It should also be noted that with this summary and the corresponding design, every attempt has been made to minimize any negative impacts on the downstream receiving waters. With the incorporation of the green roof, the site will discharge a lower sediment load and less runoff than existing conditions. We understand that review by the City of Fort Collins is to assure general compliance with standardized criteria contained in the Fort Collins Stormwater Criteria Manual (FCSCM). This letter was prepared in compliance with technical criteria set forth in both the Urban Drainage and Flood Control District (UDFCD) Urban Storm Drainage Criteria Manual and the FCSCM. If you should have any questions or comments as you review this drainage summary, please feel free to contact us at your convenience. Sincerely, United Civil Design Group, LLC Kevin Brazelton, PE Engineering Manager APPENDIX A Hydrology Calculations 401 South Mason Street Loveland, CO Runoff Summary Area Q2 Q100 (acre) (cfs) (cfs) A1 A1 0.06 60% 0.36 0.56 0.07 0.36 OS1 OS1 0.08 85% 0.63 0.75 0.15 0.61 OS2 OS2 0.10 93% 0.75 0.85 0.21 0.82 Onsite Total 0.24 81% 0.58 0.71 0.42 1.80 A1 A1 0.06 0.88 0.68 0.79 0.13 0.51 OS1 OS1 0.08 77% 0.53 0.67 0.12 0.55 OS2 OS2 0.10 83% 0.61 0.73 0.17 0.71 Onsite Total 0.24 82% 0.60 0.72 0.42 1.77 Proposed Onsite Basins Existing Onsite Basins C100 C2 Basin %I Design Point Calculations by: KRB Date: 10/9/2013 D:\Dropbox\U13008-401 Mason\Drainage\Hydrology\U13008-Runoff.xlsx 401 South Mason Street Fort Collins, CO Runoff Coefficients and % Impervious Roof (1) Walks(1) Streets(1) Landscape(1&3) %I = 90% %I = 90% %I =100% %I=2% acres sf sf sf sf sf C2 C100 Proposed Onsite Basins A1 A1 0.065 2829 1859 0 0 970 60% 0.36 0.56 OS1 OS1 0.083 3596 0 760 2346 490 85% 0.63 0.75 OS2 OS2 0.097 4244 0 1042 2993 209 93% 0.75 0.85 Onsite Total 0.245 10669 1859 1802 5339 1669 81% 0.58 0.71 Existing Onsite Basins A1 A1 0.065 2829 1847 0 832 150 88% 0.68 0.79 OS1 OS1 0.083 3596 0 442 2346 808 77% 0.53 0.67 OS2 OS2 0.097 4244 0 584 2993 667 83% 0.61 0.73 Onsite Total 0.245 10669 1847 1026 6171 1625 82% 0.60 0.72 Notes: (1) Recommended % Imperviousness Values from USDCM Vol 1 - Ch 5 - Table RO-3. Increased Lawns from 0% to 2% Impervious. (2) Runoff C is based on %I, UDFCD Eq RO-7 and correction factors in Table RO-4. (3) The landscaped area of Basin A1 denotes the approximate area of green roof being proposed with this project. Composite Runoff Basin Coefficients (2) Areas Composite Imperviousness (%I) Total Total Design Pt. Calculations by: KRB Date: 10/9/2013 D:\Dropbox\U13008-401 Mason\Drainage\Hydrology\U13008-Runoff.xlsx 401 South Mason Street Fort Collins, CO Time of Concentration Area Length Slope ti (2) Length Slope Velocity (3) t t (4) Check tc? Total Length tc (5) acres ft % min ft % fps min min u = urban ft min min Proposed Onsite Basins A1 A1 2,829 Roof 0.73 55 2 3.9 10 2 20 2.8 0.1 4.0 u 65 10 5 OS1 OS1 3,596 Street 0.90 30 4 1.2 35 0.2 20 0.9 0.7 1.9 u 65 10 5 OS2 OS2 4,244 Street 0.90 27 5 1.1 43 0.2 20 0.9 0.8 1.9 u 70 10 5 Existing Onsite Basins A1 A1 2,829 Roof 0.73 60 2 4.1 21 0.6 20 1.5 0.2 4.3 u 81 10 5 OS1 OS1 3,596 Street 0.90 30 4 1.2 35 0.2 20 0.9 0.7 1.9 u 65 10 5 OS2 OS2 4,244 Street 0.90 27 5 1.1 43 0.2 20 0.9 0.8 1.9 u 70 10 5 Notes: (1) C5 based initial ground type and Table RO-5 (4) tt =L/(V*60 sec/min) (2) ti = [1.8(1.1-C5 )L 1/2 ]/S 1/3 , S= slope in %, L=length of overland flow (400' max) (5) tc check (for urban or developed areas only) = total length/180 + 10 (3) V=Cv S 0.5 , S=watercourse slope in ft/ft, UDFCD Equation RO-4 (6) min tc = 5 min Final tc (6) tc Check for Urbanized Basin Initial Overland Flow Time (ti) Travel/Channelized Time of Flow (tt) Design Pt. 401 South Mason Street Fort Collins, CO Rational Method Peak Runoff Final tc (6) I2 I100 Q2 Q100 sf min in/hr in/hr cfs cfs Proposed Onsite Basins A1 2,829 5 0.36 0.56 2.85 9.95 0.068 0.364 OS1 3,596 5 0.63 0.75 2.85 9.95 0.147 0.613 OS2 4,244 5 0.75 0.85 2.85 9.95 0.209 0.820 Onsite Total 10,669 0.424 1.796 Existing Onsite Basins A1 A1 2,829 5 0.68 0.79 2.85 9.95 0.126 0.510 OS1 OS1 3,596 5 0.53 0.67 2.85 9.95 0.124 0.552 OS2 OS2 4,244 5 0.61 0.73 2.85 9.95 0.169 0.710 Onsite Total 10,669 0.419 1.771 Design Pt. Peak Discharge Area Basin Runoff Coefficients Rainfall Intensity C2 C100 Calculations by: KRB Date: 10/9/2013 D:\Dropbox\U13008-401 Mason\Drainage\Hydrology\U13008-Runoff.xlsx APPENDIX B LID Water Quality Calculations Sheet 1 of 2 Designer: Company: Date: Project: Location: 1. Basin Storage Volume A) Effective Imperviousness of Tributary Area, Ia Ia = 60.0 % (100% if all paved and roofed areas upstream of rain garden) B) Tributary Area's Imperviousness Ratio (i = Ia/100) i = 0.600 C) Water Quality Capture Volume (WQCV) for a 12-hour Drain Time WQCV = 0.19 watershed inches (WQCV= 0.8 * (0.91* i3 - 1.19 * i2 + 0.78 * i) D) Contributing Watershed Area (including rain garden area) Area = 2,829 sq ft E) Water Quality Capture Volume (WQCV) Design Volume VWQCV = cu ft Vol = (WQCV / 12) * Area F) For Watersheds Outside of the Denver Region, Depth of d6 = 0.60 in Average Runoff Producing Storm G) For Watersheds Outside of the Denver Region, VWQCV OTHER = 62 cu ft Water Quality Capture Volume (WQCV) Design Volume H) User Input of Water Quality Capture Volume (WQCV) Design Volume VWQCV USER = cu ft (Only if a different WQCV Design Volume is desired) 2. Basin Geometry A) WQCV Depth (12-inch maximum) DWQCV = 0.25 in B) Rain Garden Side Slopes (Z = 4 min., horiz. dist per unit vertical) Z = 0.00 ft / ft (Use "0" if rain garden has vertical walls) C) Mimimum Flat Surface Area AMin = 41 sq ft D) Actual Flat Surface Area AActual = 970 sq ft E) Area at Design Depth (Top Surface Area) ATop = 970 sq ft F) Rain Garden Total Volume VT= 20 cu ft (VT= ((ATop + AActual) / 2) * Depth) 3. Growing Media 4. Underdrain System A) Are underdrains provided? B) Underdrain system orifice diameter for 12 hour drain time i) Distance From Lowest Elevation of the Storage y = 2.50 ft Volume to the Center of the Orifice ii) Volume to Drain in 12 Hours Vol12 = 62 cu ft iii) Orifice Diameter, 3/8" Minimum DO = 0.17 in MINIMUM DIAMETER = 3/8" Design Procedure Form: Rain Garden (RG) KRB United Civil Design Group, LLC. October 9, 2013 401 South Mason Street Basin A1 Choose One Choose One 18" Rain Garden Growing Media Other (Explain): YES NO UD-BMP_v3.02_RG-Basin 1.xls, RG 10/9/2013, 9:16 AM Sheet 2 of 2 Designer: Company: Date: Project: Location: 5. Impermeable Geomembrane Liner and Geotextile Separator Fabric A) Is an impermeable liner provided due to proximity of structures or groundwater contamination? 6. Inlet / Outlet Control A) Inlet Control 7. Vegetation 8. Irrigation NO SPRINKLER HEADS ON THE FLAT SURFACE A) Will the rain garden be irrigated? Notes: Design Procedure Form: Rain Garden (RG) KRB United Civil Design Group, LLC. October 9, 2013 401 South Mason Street Basin A1 Choose One Choose One Choose One Sheet Flow- No Energy Dissipation Required Concentrated Flow- Energy Dissipation Provided Plantings Seed (Plan for frequent weed control) Sand Grown or Other High Infiltration Sod Choose One YES NO YES NO UD-BMP_v3.02_RG-Basin 1.xls, RG 10/9/2013, 9:16 AM APPENDIX C Drainage Exhibits X X X X X LOT 7 LOT 8 CITY HIGH RISK FLOODWAY CITY HIGH RISK FLOODWAY CITY HIGH RISK 100-YEAR FLOODPLAIN EXISTING LOT LINE EXISTING INLET EXISTING INLET 100-YEAR FLOOD ELEVATION-4994 (FTC NVDG-29) FLOODPLAIN CROSS SECTION #2446 FLOODPLAIN CROSS SECTION #2510 100-YEAR FLOOD ELEVATION-4993 (FTC NVDG-29) A1 OS1 OS2 PREPARED FOR: DATE SUBMITTED: The engineer preparing these plans will not be responsible for, or liable for, unauthorized changes to or uses of these plans. All changes to the plans must be in writing and must be approved by the preparer of these plans. CAUTION COIN STREET MASON, LLC. 10/9/2013 401 SOUTH MASON STREET 7 U13008 PRELIMINARY PLANS NOT FOR CONSTRUCTION Civil Engineering & Consulting 1501 Academy Court, Suite 203 Fort Collins, CO 80524 (970) 300-2508 www.unitedcivil.com NONE KEVIN D:\DROPBOX\U13008-401 MASON\CADD\ET HISTORIC DRAINAGE EXHIBIT.DWG 10/9/2013 8:45:01 AM SME HISTORIC DRAINAGE EXHIBIT DR-1 N/A 10' 1 LEGEND NOTES 1. PORTIONS OF THIS PROJECT ARE LOCATED WITHIN A CITY-REGULATED FLOODWAY AND FLOOD FRINGE OF THE OLD TOWN BASIN AND IS SUBJECT TO THE REQUIREMENTS OF CHAPTER 10 OF THE CITY CODE. EXISTING CURB & GUTTER EXISTING CONCRETE EXISTING BUILDING EXISTING PROPERTY LINE EXISTING LOT LINE EXISTING FENCE EXISTING GRAVEL EXISTING PAVEMENT STRIPING EXISTING WATER X X X X X LOT 7 LOT 8 CITY HIGH RISK FLOODWAY CITY HIGH RISK FLOODWAY CITY HIGH RISK 100-YEAR FLOODPLAIN EXISTING LOT LINE EXISTING INLET EXISTING INLET 100-YEAR FLOOD ELEVATION-4994 (FTC NVDG-29) FLOODPLAIN CROSS SECTION #2446 FLOODPLAIN CROSS SECTION #2510 100-YEAR FLOOD ELEVATION-4993 (FTC NVDG-29) FFE=92.60 A1 OS1 OS2 PREPARED FOR: DATE SUBMITTED: The engineer preparing these plans will not be responsible for, or liable for, unauthorized changes to or uses of these plans. All changes to the plans must be in writing and must be approved by the preparer of these plans. CAUTION COIN STREET MASON, LLC. 10/9/2013 401 SOUTH MASON STREET 7 U13008 PRELIMINARY PLANS NOT FOR CONSTRUCTION Civil Engineering & Consulting 1501 Academy Court, Suite 203 Fort Collins, CO 80524 (970) 300-2508 www.unitedcivil.com NONE KEVIN D:\DROPBOX\U13008-401 MASON\CADD\CP C5.00_DRAINAGE.DWG 10/8/2013 4:39:34 PM SME DRAINAGE EXHIBIT C5.00 N/A 10' 0 10' 20' SCALE: 1" = 10' 5' CHECKED BY: CHECKED BY: CHECKED BY: CHECKED BY: CHECKED BY: APPROVED: LEGEND NOTES 1. PORTIONS OF THIS PROJECT ARE LOCATED WITHIN A CITY-REGULATED FLOODWAY AND FLOOD FRINGE OF THE OLD TOWN BASIN AND IS SUBJECT TO THE REQUIREMENTS OF CHAPTER 10 OF THE CITY CODE. 2. THE FIRST FLOOR OF THE PROPOSED MIXED-USE BUILDING IS BEING FLOOD PROOFED. REFER TO ARCHITECTURAL PLANS FOR FLOOD PROOFING DETAILS AND SPECIFICATIONS. ALL FLOOD PROOFING MEASURES SHALL ADHERE TO SECTION 10-38 OF CITY CODE AND THE REQUIREMENTS SET FORTH WITHIN THE CITY'S "FLOODPROOFING GUIDELINES". A FLOOD PROOFING CERTIFICATE WILL BE REQUIRED PRIOR TO THE ISSUANCE OF A CERTIFICATE OF OCCUPANCY. 3. ALL DEVELOPMENT WITHIN THE CITY REGULATORY FLOODWAY MUST BE PRECEDED BY AN APPROVED FLOODPLAIN USE PERMIT AND $25 FEE. 4. ALL DEVELOPMENT WITHIN THE CITY REGULATORY FLOODWAY MUST BE PRECEDED BY AN APPROVED NO-RISE CERTIFICATION FOLLOWED BY RE-CERTIFICATIONOF NO-RISE IN THE AS-BUILT CONDITION. 5. ALL SPOT ELEVATIONS AND BASE FLOOD ELEVATIONS AS SHOWN ON THIS DRAWING ARE PER CITY OF FORT COLLINS VERTICAL CONTROL DATUM (NVDG 29 - UNADJUSTED). 6. NO STORAGE OF MATERIAL OR EQUIPMENT MAY OCCUR AT ANY TIME IN THE FLOODWAY BEFORE, DURING OR AFTER CONSTRUCTION. LIMITS OF DISTURBANCE EXISTING CURB & GUTTER EXISTING CONCRETE EXISTING BUILDING EXISTING PROPERTY LINE EXISTING LOT LINE EXISTING FENCE EXISTING GRAVEL EXISTING PAVEMENT STRIPING EXISTING WATER EXISTING SANITARY EXISTING OVERHEAD ELECTRIC EXISTING CABLE TV EXISTING ELECTRIC EXISTING STORM SEWER EXISTING GAS BASIN DESIGNATION BASIN AREA (ACRE) 2 - YR RUNOFF COEFF. 100 - YR RUNOFF COEFF. BASIN BOUNDARY DESIGN POINT FLOW DIRECTION EXISTING CONTOUR PROPOSED CONTOUR CITY HIGH RISK FLOODWAY CITY HIGH RISK 100-YEAR FLOODPLAIN RUNOFF SUMMARY Basin Design Point Area %I C2 C100 Q2 Q100 (acre) (cfs) (cfs) A1 A1 0.06 60% 0.36 0.56 0.07 0.36 OS1 OS1 0.08 85% 0.63 0.75 0.15 0.61 OS2 OS2 0.10 93% 0.75 0.85 0.21 0.82 Onsite Total 0.24 81% 0.58 0.71 0.42 1.80 A1 A1 0.06 0.88 0.68 0.79 0.13 0.51 OS1 OS1 0.08 77% 0.53 0.67 0.12 0.55 OS2 OS2 0.10 83% 0.61 0.73 0.17 0.71 Onsite Total 0.24 82% 0.60 0.72 0.42 1.77 EXISTING SANITARY EXISTING OVERHEAD ELECTRIC EXISTING CABLE TV EXISTING ELECTRIC EXISTING STORM SEWER EXISTING GAS BASIN DESIGNATION BASIN AREA (ACRE) 2 - YR RUNOFF COEFF. 100 - YR RUNOFF COEFF. BASIN BOUNDARY DESIGN POINT FLOW DIRECTION EXISTING CONTOUR CITY HIGH RISK FLOODWAY CITY HIGH RISK 100-YEAR FLOODPLAIN 0 10' 20' SCALE: 1" = 10' 5' RUNOFF SUMMARY Basin Design Point Area %I C2 C100 Q2 Q100 (acre) (cfs) (cfs) A1 A1 0.06 60% 0.36 0.56 0.07 0.36 OS1 OS1 0.08 85% 0.63 0.75 0.15 0.61 OS2 OS2 0.10 93% 0.75 0.85 0.21 0.82 Onsite Total 0.24 81% 0.58 0.71 0.42 1.80 A1 A1 0.06 0.88 0.68 0.79 0.13 0.51 OS1 OS1 0.08 77% 0.53 0.67 0.12 0.55 OS2 OS2 0.10 83% 0.61 0.73 0.17 0.71 Onsite Total 0.24 82% 0.60 0.72 0.42 1.77 Initial Ground Type C5 (1) Cv ti+tt Calculations by: KRB Date: 10/9/2013 D:\Dropbox\U13008-401 Mason\Drainage\Hydrology\U13008-Runoff.xlsx