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Home My WebLink AboutTESTA BEAUTY SALON, 1635 S. LEMAY AVE. - PDP - 12-07 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFinal Drainage and Erosion Control Report DMW Civil Engineers, Inc. 1635 South Lemay Avenue May 15, 2007 REFERENCES 1) Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Fort Collins, Colorado, May, 1997, revised 1999. 2) Soil Survey of Larimer County Area, Colorado, United States Department of Agriculture, December 1980. 3) Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, Wright Water Engineers, Denver, Colorado, June, 2001. 4) Spring Creek Master Drainage Plan, Baseline Hydrologic Analyses, Volumes I & II, Anderson Consulting Engineers, Inc., Fort Collins, Colorado, May 5, 2003. 5) Hydrologic Modeling and Hydraulic Analyses for Spring Creek Downstream of Edora Park, Anderson Consulting Engineers, Inc., Fort Collins, Colorado, October 21, 2005. Page 7 d Final Drainage and Erosion Control Report DMW Civil Engineers, Inc. 1635 South Lemay Avenue May 15, 2007 floodproofed to 6" above the base flood elevation. A detailed cost list will need to be provided with the building permit application to determine the value'of the remodel. Base flood elevations on the plans are referenced to the NAVD 1988 datum. The FEMA recognized vertical datum offset to NGVD 1929 (unadjusted) for the Spring Creek floodplain is three (3.0) feet (i.e.: NAVD88=NGVD29+3.0). VI. CONCLUSIONS 6.1 .Compliance with Standards II drainage analyses have been performed according to the City of Fort Collins' Storm Drainage Design Criteria and Construction Standards manual and the Urban Storm Drainage Criteria Manual, Volume 3, by the Urban Drainage and Flood Control District. Floodproofing shall meet the requirements of City of Fort Collins City Code chapter 10. There will not be any critical facilities on this site per the definition in the City of Fort Collins City Code chapter 10. Page 6 Final Drainage and Erosion Control Report 1635 South Lemay Avenue May 15, 2007 DMW Civil Engineers, Inc. surrounding the areas of construction, wattle filters, and a temporary sediment control pond. All temporary structural sediment control measures shall be inspected and maintained as needed after every storm event. See the Grading and Erosion Control Plan for locations of proposed sediment control measures. 5.5 Water Qualitv The City of Fort Collins requests that 40 hour extended detention basins be used for water quality. Because of physical restraints of this site, this BMP was not practical. Constructability was a factor when evaluating the 40 hour extended detention basin. Because of the low flows routed through this pond, orifice sizing and trash rack construction would have been difficult. Also, a typical water quality outlet structure would require an outfall pipe that would have to cross private property. It was for these reasons that a porous landscape detention basin was used for water quality. The porous landscape detention consists of a low lying vegetated area underlain by a sand bed. This BMP allows water quality containment volume below the invert of the detention pond outlet. Accumulated runoff ponds in the vegetated zone and gradually infiltrates into the underlying sand bed and subgrade. A total water quality containment volume of 210 cubic feet is provided for the impervious areas on the site. 5.6 Floodplain Design Considerations According to FEMA Flood Insurance Rate Map for Fort Collins, Community Panel 08069C-0983-F Revised December 19, 2006 this Parcel is partly within the FEMA Designated Flood Zone "AE". The Zone "AE" boundary is indicated on this map as shown (see FIRM Panel 08069C-0983-F included with this application for zone boundaries). The FEMA Base Flood Elevation for the existing building is 4947.9 (NAVD88) which is equivalent to 4944.9 (NGVD29). The FEMA Base Flood Elevation for the existing garage is 4948.3 (NAVD88) which is equivalent to 4945.3 (NGVD29) A floodplain use permit is required for each building and each site construction element (detention ponds, bike paths, parking lots, Utilities, etc.) in the floodplain. A FEMA elevation certificate will be need to be completed and approved prior to CO being issued for any new structures or additions in the floodplain. If the value of the remodel is less than 50% of the value of the structure, then no additional work to comply with the floodplain regulations is required. If the value meets or exceeds the 50% value, then the structure will have to be elevated or Page 5 Final Drainage and Erosion Control Report 1635 South Lemay Avenue May 15, 2007 DMW Civil Engineers, Inc. the site (conveyance element 420) occurs at approximately 3 hours and 28 minutes. Runoff calculations for the 1635 South Lemay Avenue site indicate that peak runoff rates are generated at a time of approximately five (5) minutes. Due to the site's close proximity to the main channel for the Spring Creek Basin, the peak flows generated on site significantly "beat the peak" of the main channel. Therefore, the site -generated peak flow does not significantly affect the overall peak for Spring Creek. According to the Spring Creek Master Drainage Plan, updated by Anderson Consulting Engineers, Inc. on May 5, 2003, the 1635 South Lemay Avenue site is situated in sub -basin 220. Impervious percentages for sub -basins in the Spring Creek Master Drainage Plan were generally assumed based upon current land use and zoning classifications. For example, the three zoning classifications within sub - basin 220 are NC (Neighborhood Commercial), MMN (Medium Density Mixed -Use Neighborhood), and LMN (Low Density Mixed -Use Neighborhood) and have assumed impervious percentages of 90%, 70%, and 50%, respectively. Sub -basin 220 was determined in the master plan to have an impervious percentage of 65%. Although the composite calculations are not included for each sub -basin in the Spring Creek Basin, the value for sub -basin 220 was confirmed by DMW, using the assumptions listed in the Master Plan, to be 59%. This demonstrates that the 1635 South Lemay Avenue site was assumed to have an impervious percentage of at least 90% in the Spring Creek Master Drainage Plan based upon the NC zoning of the site. DMW performed an analysis of actual conditions for the NC zoned area surrounding the 1635 South Lemay Avenue site. Of the 3.96 acre area, 1.77 acres, or 45 percent, is impervious. Therefore, the site will maintain an impervious percentage below that which was assumed in the Master Drainage Plan and will be in compliance with that plan. This demonstrates that the proposed improvements at 1635 South Lemay Avenue will not adversely affect the detention pond located at the Burlington Northern Railroad Crossing near Timberline Road and Lemay Avenue. 5.4. Erosion Control The erosion control plan presented here is intended to control rainfall erosion. The Erosion Control Reference Manual for Construction Sites (ECRM), City of Fort Collins, has been referenced for this erosion control plan. Appendix E contains worksheets for erosion control design as well as for erosion control escrow security. The proposed rainfall erosion control plan during construction will consist of minimizing soil exposure, protection of exposed soils and temporary structural sediment control measures. Temporary structural sediment control for the site will consist of silt fence Page 4 Final Drainage and Erosion Control Report DMW Civil Engineers, Inc. 1635 South Lemay Avenue May 15, 2007 V. DRAINAGE FACILITIES DESIGN 5.1 Proposed Site Development Development of the 1635 South Lemay Avenue site will consist of remodeling the structure to convert it from residential use to commercial use as a beauty salon. The proposed site infrastructure includes a new parking and sidewalks. Approximately 68% of the 0.38 acre site will be disturbed with the construction of this project. The runoff coefficient for the overall site after construction is estimated to be approximately 0.56 for the design storm. 5.2 Developed Drainage Patterns The developed site has been divided into three (3) onsite drainage basins. Stormwater runoff will be conveyed overland,, through concrete gutters and chases, and grass lined swales. • Basin 1 (0.18 acres) includes half of the building and the site west of the building. Runoff -from this basin drains to the southeast to a proposed water quality pond. The 10 and 100-year peak discharges from the basin are 0.4 and 1.1 cfs, respectively. Basin 2 (0.17 acres) includes half of the building and the site east of the building. Runoff from this basin drains to the southwest to a proposed water quality pond. The 10 and 100-year peak discharges from the basin are 0.4 and 1.3 cfs, respectively. The 10 and 100-year peak discharges from both basins into the pond are 1.0 and 2.4 cfs, respectively. Basin 3 (0.03 acres) includes the eastern portion of the site that drains to Lemay Avenue. Runoff from this basin drains to the east directly into Lemay Avenue. The 10 and 100-year peak discharges from the basin are 0.1 and 0.3 cfs, respectively. 5.3 Detention .Prior to construction, the 1635 South Lemay Avenue site had runoff coefficients of 0.34 and 0.43 for the 10 and 100-year storms, respectively. The proposed runoff coefficients for the site are 0.56 and 0.70 for the 10 and 100-year storms, respectively. The increase of runoff generated by the increase in imperviousness is 0.6 and 1.3 cfs for the 10 and 100-year storms, respectively. This increase in runoff is not detained due to the physical limitations of the site, and due to the site's close proximity to Spring Creek. The peak for this runoff for the site will occur much earlier than the peak for the Spring Creek Basin at this point. Therefore increase in the overall peak of Spring Creek attributable to the 1635 South Lemay Avenue project is negligible. Per the Spring Creek Master Drainage Plan, the peak for Spring Creek adjacent to Page 3 Final Drainage and Erosion Control Report DMW Civil Engineers, Inc. 1635 South Lemay Avenue May 15, 2007 the City of Fort Collins Master Drainage Plan. Spring Creek is a major watercourse that flows from Spring Canyon Dam at Horsetooth Reservoir to its confluence with the Poudre River. The Spring Creek drainage basin encompasses nearly nine square miles in central Fort Collins. The basin is dominated by residential development, but it also includes open space, parks and isolated areas of commercial and industrial development. 3.2 Sub -Basin Description Stormwater runoff from the 1635 South Lemay Avenue site drains overland generally from north to south at slopes ranging from 1.0% to 2.0% into adjacent property and then into Spring Creek. Stormwater runoff is currently conveyed from the existing site towards the south overland. The flows are conveyed overland directly to Spring Creek. Spring Creek ultimately discharges into the Poudre River. IV. DESIGN CRITERIA 4.1 Design Criteria and Constraints Drainage design criteria specified in the City of Fort Collins Storm Drainage Design Criteria and Construction Standards manual and the Urban Storm Drainage Criteria Manual, Volume 3 by the Urban Drainage and Flood Control District have been referenced in the preparation of this study. 4.2 Hydrologic Criteria The rational method has been used to estimate peak stormwater runoff from the project site. An initial 10-year and major 100-year design storms have been used to evaluate the proposed. drainage system. Calculations made as part of this investigation, along with other supporting material, are contained in Appendix A. Rainfall intensity data for the rational method has been taken from rainfall intensity data tables contained in the City of Fort Collins Storm Drainage Design Criteria and Construction Standards manual (see Figure 3-1 a). Composite runoff coefficients were generated using Table 3-3 and 3-4 of the City of Fort Collins Storm Drainage Design Criteria and Construction Standards manual. 4.3 Hydraulic Criteria Spreadsheets, provided by the.Urban Drainage and Flood Control District have also been used as a design aid for swales and water quality calculations. Hydraulic calculations are included in Appendix B. Page 2 i Final Drainage and Erosion Control Report for 1635 South Lemay Avenue _ Fort Collins, Colorado May 15, 2007 I. INTRODUCTION 1.1 Objective This study documents the results of a final hydrologic and hydraulic analysis of post -development conditions for the proposed 1635 South Lemay Avenue project. The utility plans which accompany this report are entitled Final Utility Plans for 1635 South Lemay Avenue prepared by DMW Civil Engineers, Inc. This report will also assist the contractor in the preparation of a Stormwater Management Plan j� (SWMP). 1.2 Mapping and Surveying Field survey information and topographic mapping with a contour interval of 1-foot was obtained by DMW Civil Engineers from Frederick Land Surveying, Loveland, Colorado. Additional topography outside of the project boundary was taken from City of Fort Collins Aerial Topography with a two (2) foot contour interval. All elevations in this report are on NGVD29 datum. FEMA flood elevations have been converted from NAVD88 to NGVD29. II GENERAL LOCATION AND DESCRIPTION 2.1 Location The site is located in the northwest quarter of Section 24, Township 7 North, Range 69 West of the 6th Principal Meridian in the City of Fort Collins, Colorado. The site is bounded by Lemay Avenue to the east, Spring Creek to the south, and developed lots to the north and west (see vicinity map). 2.2 Description of Property The 1635 South Lemay.Avenue site is approximately 0.38 acres. The existing site has approximately 60% pervious coverage which consists of irrigated turf grass and landscaping. Onsite soils are predominantly Hydrologic Group C, according to the Soil Survey for Larimer County;, by the Soil Conservation Service. The existing runoff coefficient for the overall site prior to construction is estimated to be 0.56 for the design storm. The site is zoned Neighborhood Commercial District (NC). This site is within Flood Insurance Zone AE, the areas determined to be within the 100- year flood plain according to the FEMA Flood Insurance Rate Map, Community - Panel No. 08069C-0983F, dated December 19, 2006. III. DRAINAGE BASINS AND SUB -BASINS 3.1 Major Basin Description The 1635 South Lemay Avenue site is within the Spring Creek Basin according to PROJECT LOCATION e VICINITY MAP rlqlsw:Ao SCALE: 1 "=2000' Final Drainage and Erosion Control Report for [� 1635 South Lemay Avenue _ EXHIBITS Exhibit 1 100-Year Floodplain/Floodway Map, Spring Creek Master Drainage Plan Exhibit 2 8.5"x11" FIRM, Community -Panel No.08069C-0983F Exhibit 3 24x36" Developed Drainage Plan APPENDICES Appendix A Hydrology Calculations Appendix B Hydraulic Calculations Appendix C Water Quality Pond Calculations Appendix D Impervious calculations and excerpts from the Spring Creek Master Drainage Plan Appendix E Erosion Control Calculations Final Drainage and Erosion Control Report _ for [� 1635 South Lemay Avenue - TABLE OF CONTENTS VICINITY MAP Page No. I INTRODUCTION 1.1 Objective.................................................1 1.2 Mapping and Surveying ...................................... 1 II GENERAL LOCATION AND DESCRIPTION 2.1 Location..................................................1 2.2 Description of Property .. 1 III DRAINAGE BASINS AND SUB -BASINS 3.1 Major Basin Description ...................................... 1 3.2 Sub -Basin Description ....................................... 2 IV DESIGN CRITERIA 4.1 Design Criteria and Constraints ................................ 2 4.2 Hydrologic Criteria .......................................... 2 4.3 Hydraulic Criteria ........................................... 2 V DRAINAGE FACILITIES DESIGN 5.1 Proposed Site Development .................................. 3 5.2 Developed Drainage Patterns ................................. 3 5.3 Detention.................................................3 5.4 Erosion Control ............................................ 4 5.5 Water Quality .............................................. 5 5.6 Floodplain Design Considerations .............................. 5 I� VI CONCLUSIONS 6.1 Compliance with Standards ................................... 6 REFERENCES..................................................7 J PV1MNGEERS May 15, 2007 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 Re: Final Drainage and Erosion Control Report for 1635 South Lemay Avenue Fort Collins, Colorado Dear Staff: 1435 WEST 29' STREET LOVELAND, CO 60538 (970) 461-2661 FAx (970) 461-2665 WWW. DMWCIVILENC.INEERS.COM DMW Civil Engineers, Inc. is pleased to submit this Final drainage and erosion control report for 1635 South Lemay Avenue for your review. I hereby certify that this report was prepared by me, or under my direct supervision, in accordance with the technical criteria set forth in the City of Fort Collins' Storm Drainage Design Criteria and Construction Standards manual and the Urban Storm Drainage Criteria Manual, Volume 3, by the, Urban Drainage and Flood Control District. �} We acknowledge that the City of Fort Collins''review of this study is only for general conformance with submittal requirements, current design criteria and standard engineering principles and practices. If you should have any questions or comments as you review this report, please feel free to contact me at your convenience. Sincerely, DMW CIVI GINEERS, INC. PP�O RFG�S `o`QPM/ 9` 33885 F.' Jade P. Miller, P.E. (CO #33885) Project Engineer Final Drainage and Erosion Control Report for 1635 South Lemay Avenue Fort Collins, Colorado May 15, 2007 Prepared for: Mr. John Testa 4221 Cobb Lake Drive Fort Collins, CO 80524 Prepared by: I IPMJG EERS 1; 1435 W. 29°i Street Loveland, Colorado 80538 Phone: (970)461-2661 Fax: (970)461-2665 Project Number. TBS