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HomeMy WebLinkAboutTHE SUMMIT ON COLLEGE PARKING GARAGE - MJA/FDP - FDP130056 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTPRELIMINARY DRAINAGE REPORT FOR THE SUMMIT ON COLLEGE PARKING GARAGE AT STUART STREET/CHOICE CENTER DRIVE FORT COLLINS, COLORADO FOR FORT COLLINS ASSOCIATES, L.P. 431 OFFICE PARK DRIVE BIRMINGHAM, ALABAMA 35223 DECEMBER 27, 2013 The Summit on College Parking Garage Preliminary Drainage Report Page 1 of 10 TABLE OF CONTENTS SECTION 1 – ENGINEER’S CERTIFICATION BLOCK ........................................................................ 3 SECTION 2 – SITE LOCATION AND PROJECT DESCRIPTION ............................................................ 4 BENCHMARK INFORMATION .................................................................................................. 4 SECTION 3 – STORM DRAINAGE CRITERIA .................................................................................. 5 SECTION 4 – DRAINAGE BASINS AND HISTORIC RUNOFF .............................................................. 6 HISTORIC BASINS ................................................................................................................. 6 PROPOSED DEVELOPED BASINS ............................................................................................ 6 DETENTION/WATER QUALITY POND ....................................................................................... 7 SECTION 5 – STORMWATER POLLUTION PREVENTION ................................................................... 8 TEMPORARY EROSION CONTROL .......................................................................................... 8 PERMANENT EROSION CONTROL........................................................................................... 8 SECTION 6 – CONCLUSIONS ..................................................................................................... 9 SECTION 7 – REFERENCES ....................................................................................................... 10 The Summit on College Parking Garage Preliminary Drainage Report Page 2 of 10 APPENDIX Appendix A – Hydrologic Computations 1. Site Vicinity Map 2. Soil Map - Natural Resources Conservation Services (NRCS) 3. City of Fort Collins 100 year Flood Map 4. FEMA Firmette – Panel 08069C0979H 5. Base Flood Elevation Interpolation and Exhibit 6. Figure 1- Existing Drainage Map 7. Rational Worksheets (Existing Flows) 8. Velocity Calculations for 30in RCP 9. Figure 2 - Developed Drainage Map 10. Rational Worksheets (Developed Flows) Appendix B – Referenced Information 1. Choice Center –Spring Creek LOMR Exhibits The Summit on College Parking Garage Preliminary Drainage Report Page 3 of 10 SECTION 1 – ENGINEER’S CERTIFICATION BLOCK I hereby certify that this Final Drainage Report for the Summit on College Parking Garage was prepared by me (or under my direct supervision) for the Owners thereof and meets or exceeds the criteria of the City of Fort Collins Stormwater Design Standards. Signature: ________________________________________________ Jason T. Claeys, PE Registered Professional Engineer State of Colorado No. 42122 The Summit on College Parking Garage Preliminary Drainage Report Page 4 of 10 SECTION 2 – GENERAL LOCATION AND DESCRIPTION SITE LOCATION AND PROJECT DESCRIPTION The Summit on College Parking Garage project site is located at the western termination of Stuart Street and Choice Center Drive in the City of Fort Collins, Colorado. Refer to Appendix A for the site vicinity map. The site is a portion of a property owned by Fort Collins Associates, L.P., recently developed as The Summit (previously known as Choice Center) student housing facility, and is currently occupied by a surface parking lot serving the Summit residents. In general, as part of this project, the proposed site improvements will consist of construction of a multi-tiered parking garage in place of the existing surface lot. The existing parking footprint will be retained for the ground level of the garage, with the upper levels overhanging approximately 7,685 square feet to the south. This proposed covered ground area will be utilized for additional bicycle parking and for water quality improvements. The property is located within the 100 year floodplain as shown on the City of Fort Collins Flood Map and the Federal Emergency Management Agency (FEMA) community panel # 08069C0979H, revised on May 2, 2012, attached in Appendix A. As part of the Choice Center project, a CLOMR was completed revising the floodplain and floodway boundaries of Spring Creek running to the south of the property as well as the historic drainageway located along the Burlington Northern Railroad to the west which discharges into it. The LOMR for that project is currently under final review and will be approved within 45-90 days. Refer to the Choice Center LOMR exhibits prepared by Nolte Engineers attached in Appendix B. The proposed parking garage project will proceed using the floodplain/floodway boundaries as-built with the Choice Center LOMR and the Floodplain Use Permit for that project will be amended to include the parking garage before construction commences. Base Flood Elevation was interpolated from the current Spring Creek hydrologic model provided by the City of Fort Collins. See calculations and exhibit in Appendix A. The garage itself will not be elevated to the Regulatory Flood Protection Elevation and is proposed to be vented to allow floodwaters to pass through the structure, per the requirements of the City Municipal Code, Section 10-39. The elevator located in the northeast corner of the garage will be elevated to the RFPE. A FEMA Elevation Certificate will be completed and approved before a Certificate of Occupancy is issued. The main purpose of this report is to summarize the changes in impervious area and the stormwater quality improvements associated with the site improvements for the proposed parking structure. BENCHMARK INFORMATION Horizontal datum is Colorado State Plate Coordinates NAD 83(2007) Datum and vertical datum is referenced from Fort Collins Benchmark C-322, Record Elevation = 4,986.22, NGVD 1929 (unadjusted). The Summit on College Parking Garage Preliminary Drainage Report Page 5 of 10 SECTION 3 – STORM DRAINAGE CRITERIA This report was prepared to meet or exceed the City of Fort Collins stormwater criteria. The City of Fort Collin’s Storm Drainage Design Criteria and Construction Manual (with all current 1997 Revisions and 2012 Amendments) (CoFC-SDDCCM) and the Urban Drainage Flood Control District’s (UDFCD) Drainage Criteria Manual (USDCM) Volumes 1, 2 and 3 were referenced as guidelines for this design. HYDROLOGIC CRITERIA The rational method was performed to calculate the peak historic runoff rates for each basin. The City of Fort Collins runoff coefficients were used for the analysis. Weighted percent impervious was calculated for each basin using Table RO-3 in the Urban Storm Drainage Criteria Manual. The weighted runoff coefficients were calculated for each basin using Tables 3-2 and 3-3 in the City of Fort Collins – Storm Drainage Design Criteria and Construction Standards (CoFC– SDDCCS). The time of concentration was calculated using the equations given within section 2.4.1 of the USDCM equation RO-3. The intensity was calculated using the corresponding storm rainfall depth and USDCM Equation RA-3. To account for the City of Fort Collins’ IDF Curve, Coefficient 3 of the UDFCD’s intensity formula was adjusted to 0.7867. The City of Fort Collins area has 5-yr 1-hr rainfall depth of 1.14 inches, a 10-yr 1 hr rainfall depth of 1.40 inches and a 100-yr 1 hr rainfall depth of 2.86 inches. These depths do account for the 1997 adjusted rainfall depths. The Summit on College Parking Garage Preliminary Drainage Report Page 6 of 10 SECTION 4 – DRAINAGE BASINS AND HISTORIC RUNOFF HISTORIC BASINS Currently, the northeast portion of the existing parking lot, designated sub-basin H1, drains to a combination type-13 concrete inlet at the intersection of Choice Center Drive and Stuart Street, shown on the attached Existing Drainage Figure 1 in Appendix A. This runoff is conveyed through an existing storm sewer system that eventually discharges into Spring Creek at a headwall in Creekside Park. The remainder of the existing site, sub-basins H2 & H3, sheet flows to the south across the lot, through a series of curb cuts and into a 20’ infiltration area followed by a grass buffer at the edge of Spring Creek. For each basin the total runoff in Cubic Feet per Second (CFS) was calculated to determine an equivalent runoff for the entire site. Rational method calculations with peak flows for the individual sub-basins are attached in Appendix A. Additionally, there is an existing 30” reinforced concrete pipe storm drain line installed as part of the Choice Center improvements that conveys overflow from the off-site pond to the west of the Burlington Northern Railroad into the low flow section of Spring Creek to the south and east. The existing alignment of this system cuts diagonally across the southwest portion of the proposed garage and must be relocated outside the structure. Consideration was given to abandoning this system since very little runoff flows through it on a daily basis, but that option was rejected due to the system’s critical role in preventing overtopping of the BNRR ROW by floodwaters during large storm events. No runoff from the proposed garage site enters this system. Due to grade constraints and the need to keep this line in service, the proposed realignment results in a slope of 0.0037 ft/ft for the two sections of pipe to be installed, for a total of 351 lineal feet. For a 30 inch reinforced concrete pipe flowing at only 3 inches depth of water, the flow velocity in the pipe is 2.04 feet per second, providing minimum cleansing velocity and eliminating the need for a variance request. See attached velocity calculations in Appendix A. PROPOSED DEVELOPED BASINS The proposed drainage patterns are to remain similar to current patterns. As before, three designated sub-basins will convey stormwater runoff to Spring Creek. Sub-basin A1 consists of the north portion of the existing surface lot and will serve as the access approach to the entrance of the garage. The runoff from this area will continue to be collected at the existing combination type-13 inlet. The proposed layout will increase flows into this inlet by approximately 0.53 cfs for the 100-yr storm event. The existing inlet has capacity to handle this flow increase. The Summit on College Parking Garage Preliminary Drainage Report Page 7 of 10 Sub-basins A2 and A3 represent the runoff collected from the open top tier of the proposed garage that will be piped to the existing ground surface and into a proposed water quality pond located at the south end of the structure, in the vicinity of the existing grass buffer/infiltration area. A bio- swale and underdrain is proposed to provide water quality treatment, ultimately draining through an outlet structure that will discharge into the existing storm sewer system and Spring Creek. The weighted historic and developed percent impervious was calculated based on the current City of Fort Collins Stormwater Criteria Manual and the Urban Storm Drainage Criteria Manual. The weighted percent impervious and composite runoff coefficient calculations, along with the rational calculations are attached for reference. The existing site has an overall percent impervious of 80.1%, and the proposed improvements will increase the percent impervious to 99.7% (+19.6%). The increase in impervious area is due to the increase in the proposed garage top level footprint versus the existing surface lot footprint. DETENTION/WATER QUALITY POND On-site storm water detention is not required. Refer to the Final Drainage and Erosion Control Report for Choice Center, prepared by Jim Sell Design, Inc., dated August 1, 2011. The property occupied by the Summit student housing facility, an area defined as SWMM basin 122 in the Hydrologic Modeling and Hydraulic Analyses and Revised Flood Hazard Mapping for Spring Creek, dated February 8, 2006, was modeled pre-development for an assumed imperviousness of 75%. Because the Choice Center improvements resulted in an overall impervious of 68%, no runoff detention was required. The portion of the Choice Center site that is the proposed parking garage represents 8.8% of the total developed site area. The increase in impervious area on this portion of the site (19.6%) is equivalent to less than 1% increase in impervious area on the entire Choice Center site, for a total of ±69% impervious area. This is still less than the modeled 75% for the same area defined as SWMM basin 122, and therefore does not require any runoff to be detained. The proposed water quality pond has been designed to capture stormwater runoff from basins A2 and A3. Water Quality Capture Volume (WQCV) requirement was calculated to be 0.044 AC-FT based on UDFCD Best Management Practice calculation spreadsheet. The Summit on College Parking Garage Preliminary Drainage Report Page 8 of 10 SECTION 5 – STORMWATER POLLUTION PREVENTION TEMPORARY EROSION CONTROL A temporary erosion control plan is to be implemented for the site during construction. Temporary erosion control measures include, but not limited to, slope and swale protection provided by the use of erosion control wattles/sediment control logs, inlet protection, etc. All temporary erosion control measures are to be removed after they are deemed unnecessary. PERMANENT EROSION CONTROL Permanent erosion control measures include, but not limited to, the constructed water quality pond, riprap pads placed for culvert outlet protection, seeding and mulch placed to enable and established vegetative growth, etc. Long-term maintenance of these erosion control measures shall be the responsibility of the owner of the property. The Summit on College Parking Garage Preliminary Drainage Report Page 9 of 10 SECTION 6 – CONCLUSIONS This Drainage Report for the Summit on College Parking Garage has been prepared to comply with the stormwater criteria set by the City of Fort Collins. The proposed drainage systems presented in this report are designed to convey the proposed peak stormwater runoff through the site to the proposed water quality pond and the existing storm sewer system at Stuart Street. Through calculations and review of the existing storm drain system, there is adequate capacity to convey the proposed flows. This report also proposes best management practices for erosion control, permanent landscaping, riprap, and on-site construction facilities. It can therefore be concluded that the proposed parking garage development complies with all of the stormwater jurisdictional criteria and will not adversely affect the existing streets, storm drain system, or Spring Creek floodplain/floodway. The Summit on College Parking Garage Preliminary Drainage Report Page 10 of 10 SECTION 7 – REFERENCES 1. Urban Storm Drainage Criteria Manual (Volumes 1, 2, and 3), Urban Drainage and Flood Control District, June 2001, Revised April 2008. 2. Storm Drainage Criteria Manual and Construction Standards, City of Fort Collins Storm Water Utility, City of Fort Collins, Colorado, Updated January, 1997 with 2012 amendments. 3. “Hydrologic Group Rating for Larimer County Area, Colorado”, USDA-Natural Resources Conservation Service, National Cooperative Soil Survey. Web Soil Survey URL: http://websoilsurvey.nrcs.usda.gov. [12/12/2013] 4. Drainage and Erosion Control Report for Choice Center, prepared by Jim Sell Design, Inc., Dated August 1, 2011 APPENDIX A – HYDROLOGIC COMPUTATIONS 1. Site Vicinity Map 2. Soil Map - Natural Resources Conservation Services (NRCS) 3. City of Fort Collins 100 year Flood Map 4. FEMA Firmette – Panel 08069C0979H 5. Base Flood Elevation Interpolation and Exhibit 6. Figure 1- Existing Drainage Map 7. Rational Worksheets (Existing Flows) 8. Velocity Calculations for 30in RCP 9. Figure 2 - Developed Drainage Map 10. Rational Worksheets (Developed Flows) THE SUMMIT ON COLLEGE PARKING GARAGE FORT COLLINS, COLORADO VICINITY MAP NOT TO SCALE The Summit on College Parking Garage City of Fort Collins Flood Map This map is a user generated static output from the City of Fort Collins FCMaps Internet mapping site and is for reference only. Data layers that appear on this map may or may not be accurate, current, or otherwise reliable. 9,452 City of Fort Collins - GIS 0.3 1: WGS_1984_Web_Mercator_Auxiliary_Sphere 0 0.15 0.3 Miles Notes Legend Parcels FEMA Floodplain FEMA High Risk - Floodway FEMA High Risk - 100 Year FEMA Moderate Risk - 100 / 500 Year City Floodplains City High Risk - Floodway City High Risk - 100 Year City Moderate Risk - 100 Year City Limits THE SUMMIT PARKING GARAGE Base Flood Elevation Determination Design Engineer: Design Firm: Project Number: Date: DESIGN CRITERIA FEMA Firm Map # 08069C0979H Effective Date: May 2, 2012 Spring Creek HEC-RAS Model from Spring Creek PMR BFE ELEVATION (FT) XS STATION (FT) Floodplain Fringe Velocity (FPS) 4982.060 16069 1.560 4982.880 16198 2.610 4984.710 16451 0.000 BFE Interpolation based on determined drainage way station from current effective HEC-RAS model alignment Station Interpolated BFE Elevation (NGVD 29) Interpolated BFE Elevation (NAVD 88) Interpolated Floodplain Fringe Velocity (FPS) 161+61.95 4982.65 4985.63 2.32 Furthest Upstream (Southwest) Building Corner 163+37.01 4983.89 4986.87 1.18 Southeast Building Corner Description K. Brigman JVA Inc. 1788.5c December 12, 2013 1788.5c Base Flood Elevation Interpolation Page 1 of 1 12/12/13 The Summit on College Parking Garage PROPOSED COMPOSITE C AND IMPERVIOUS AREA CALCULATION Design Engineer: Design Firm: Project Number: Date: DESIGN CRITERIA: Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised April 2008) BASINS: C2 C5 C100 0.71 0.73 0.81 0.04 0.10 0.38 0.89 0.90 0.96 0.71 0.73 0.81 0.02 0.08 0.35 Sub-basin Atotal Aroof Aparks Apaved Awalk Alawn Designation (acres) (acres) (acres) (acres) (acres) (acres) C2 C5 C100 H1 0.15 0.00 0.01 0.14 0.00 0.00 94.4% 0.78 0.80 0.87 H2 0.74 0.00 0.03 0.71 0.00 0.00 96.8% 0.82 0.84 0.90 H3 0.19 0.00 0.19 0.00 0.00 0.00 5.0% 0.04 0.10 0.38 Historic Overall 1.08 0.00 0.23 0.86 0.00 0.00 80.1% 0.57 0.60 0.70 A1 0.20 0.00 0.00 0.17 0.03 0.00 98.6% 0.86 0.87 0.93 A2 0.61 0.00 0.00 0.61 0.00 0.00 100.0% 0.89 0.90 0.96 A3 0.27 0.00 0.00 0.27 0.00 0.00 100.0% 0.89 0.90 0.96 Proposed Overall 1.08 0.00 0.00 1.05 0.03 0.00 99.7% 0.88 0.89 0.95 % Impervious values from Table RO-3 and C Values obtained from Table RO-5 in the Urban Storm Drainage Criteria Manual C VALUE Land Use % Impervious Roofs 90.0% for Hydrologic Soil Classification B K. Brigman JVA, Inc. 1788.5c December 12, 2013 City of Fort Collins Stormwater Criteria Manual (Ordinance No. 174, 2011) Weighted % COMPOSITE Impervious Streets Parks 100.0% Lawns 0.0% 5.0% Drives & Walks 90.0% JVA, Incorporated 25 Old Town Sq, Suite 200 Fort Collins, CO 80524 Ph: 970.225.9099 Fax: 970.225.6923 1788.5c Proposed Rational - COMPOSITE C Page 1 of 1 JVA, Inc. The Summit on College Parking Garage PROPOSED DRAINAGE SUMMARY Design Engineer: Design Firm: Project Number: Date: DRAINAGE BASIN SUMMARY TABLE 1 H1 0.15 0.78 0.80 0.87 5.00 0.33 0.47 1.28 2 H2 0.74 0.82 0.84 0.90 8.12 1.45 2.05 5.56 3 H3 0.19 0.04 0.10 0.38 10.76 0.02 0.06 0.55 Historic Overall 1.08 0.57 0.60 0.70 1.80 2.58 7.39 1 A1 0.20 0.86 0.87 0.93 5.00 0.48 0.67 1.81 2 A2 0.61 0.89 0.90 0.96 5.00 1.49 2.10 5.62 3 A3 0.27 0.89 0.90 0.96 5.00 0.67 0.95 2.54 Proposed Overall 1.08 0.88 0.89 0.95 2.65 3.72 9.97 Q100 (cfs) DRAINAGE REMARKS DESIGN POINT TRIBUTARY SUB-BASIN AREA (acres) C2 C5 K. Brigman JVA, Inc. 1788.5c Q5 (cfs) December 12, 2013 Q2 (cfs) tc (min) C100 JVA, Incorporated 25 Old Town Sq, Suite 200 Fort Collins, CO 80524 Ph: 970.225.9099 Fax: 970.225.6923 1788.5c Proposed Rational - Summary Page 1 of 1 JVA, Inc. The Summit on College Parking Garage RATIONAL METHOD - 5 YEAR PROPOSED STORM Design Engineer: Design Firm: Project Number: Date: DESIGN CRITERIA: Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised April 2008) EQUATIONS: Q5 = 5-yr peak discharge (cfs) I = rainfall intensity (in/hr) C5 = 5-yr runoff coefficient P1 = one-hour point rainfall depth (in) I5 = 5-yr rainfall intensity (in/hr) tc = time of concentration (min) A = drainage area (ac) P1-5yr = 1.14 in. BASINS: Design Sub-basin AREA Runoff tc C(A) I Q5 ΣΣΣΣQ5 Point Ac Coeff. (C5 ) Min Ac In/Hr Cfs Cfs 1 H1 0.15 0.80 5.00 0.12 3.86 0.47 0.47 2 H2 0.74 0.84 8.12 0.62 3.33 2.05 2.52 3 H3 0.19 0.10 10.76 0.02 2.99 0.06 2.58 1 A1 0.20 0.87 5.00 0.17 3.86 0.67 0.67 2 A2 0.61 0.90 5.00 0.54 3.86 2.10 2.77 3 A3 0.27 0.90 5.00 0.25 3.86 0.95 3.72 DIRECT RUNOFF Note 3.35 cfs/acre 2.78 cfs/acre 0.30 cfs/acre K. Brigman JVA, Inc. 1788.5c December 12, 2013 City of Fort Collins Stormwater Criteria Manual (Ordinance No. 174, 2011) 3.46 cfs/acre 3.07 cfs/acre 3.46 cfs/acre JVA, Incorporated 25 Old Town Sq, Suite 200 Fort Collins, CO 80524 Ph: 970.225.9099 Fax: 970.225.6923 1788.5c Proposed Rational - 5-yr Storm Drainage Page 1 of 1 JVA, Inc. The Summit on College Parking Garage RATIONAL METHOD - 100 YEAR PROPOSED STORM Design Engineer: Design Firm: Project Number: Date: DESIGN CRITERIA: Urban Storm Drainage Criteria Manual by Urban Drainage and Flood Control District, June 2001 (Revised April 2008) EQUATIONS: Q100 = 100-yr peak discharge (cfs) I = rainfall intensity (in/hr) C100 = 100-yr runoff coefficient P1 = one-hour point rainfall depth (in) I100 = 100-yr rainfall intensity (in/hr) tc = time of concentration (min) A = drainage area (ac) P1-100yr = 2.86 in. BASINS: Design Sub-basin AREA Runoff tc C(A) I Q100 ΣΣΣΣQ100 Point Ac Coeff. (C100 ) Min Ac In/Hr Cfs Cfs 1 H1 0.15 0.87 5.00 0.13 9.68 1.28 1.28 2 H2 0.74 0.90 8.12 0.67 8.35 5.56 6.84 3 H3 0.19 0.38 10.76 0.07 7.50 0.55 7.39 1 A1 0.20 0.93 5.00 0.19 9.68 1.81 1.81 2 A2 0.61 0.96 5.00 0.58 9.68 5.62 7.43 3 A3 0.27 0.96 5.00 0.26 9.68 2.54 9.97 DIRECT RUNOFF Note 9.02 cfs/acre 7.54 cfs/acre 2.84 cfs/acre K. Brigman JVA, Inc. 1788.5c December 12, 2013 City of Fort Collins Stormwater Criteria Manual (Ordinance No. 174, 2011) 9.25 cfs/acre 8.42 cfs/acre 9.25 cfs/acre JVA, Incorporated 25 Old Town Sq, Suite 200 Fort Collins, CO 80524 Ph: 970.225.9099 Fax: 970.225.6923 1788.5c Proposed Rational - 100-yr Storm Drainage Page 1 of 1 JVA, Inc. Worksheet Worksheet for Circular Channel untitled.fm2 12/18/13 03:29:38 PM JVA, Inc © Haestad Methods, Inc. 37 Brookside Road Waterbury, CT 06708 USA +1-203-755-1666 Project Engineer: Kevin Tone FlowMaster v7.0 [7.0005] Page 1 of 1 Project Description Worksheet Circular Channel - 1 Flow Element Circular Channel Method Manning's Formula Solve For Discharge Input Data Mannings Coefficient 0.013 Channel Slope 0.003700 ft/ft Depth 0.25 ft Diameter 30.0 in Results Discharge 0.52 cfs Flow Area 0.3 ft² Wetted Perimeter 1.61 ft Top Width 0.00 ft Critical Depth 0.23 ft Percent Full 10.0 % Critical Slope 0.004944 ft/ft Velocity 2.04 ft/s Velocity Head 0.06 ft Specific Energy 0.31 ft Froude Number 0.87 Maximum Discharge 26.84 cfs Discharge Full 24.95 cfs Slope Full 0.000002 ft/ft Flow Type Subcritical APPENDIX B – REFERENCED INFORMATION 1. Choice Center – Spring Creek LOMR Exhibits