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Home My WebLink About637 COWAN STREET - PDP - 21-03 - REPORTS - DRAINAGE REPORT(� 295� A�01:f- �i3�, Drainage Design Considerations 637 Cowan Street November 5, 2003 REFERENCES DMW Civil Engineers, Inc. 1) Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, May, 1997, revised 1999 2) Urban Storm Drainage Criteria Manual, Urban Drainage and Flood Control District, Wright McLaughlin Engineers, Denver, Colorado, June, 2001. Page 5 Drainage Design Considerations DMW Civil Engineers, Inc. ! 637 Cowan Street November 5, 2003 ! Vill. CONCLUSIONS 8.1 Compliance with Standards All 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. M Drainage Design Considerations DMW Civil Engineers, Inc. ! 637 Cowan Street November 5, 2003 ! 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. 5.3 Hydraulic Criteria ' The computer program "Flowmaster" has been used to analyze the capacity of proposed pipes and chases for the site. VI. EROSION CONTROL 6.1 Erosion Control Plan and Criteria ' 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. - The proposed rainfall erosion control plan during construction will consist of ' temporary structural erosion control measures. Temporary sediment control consisting of silt fencing will surround areas of the proposed construction. In addition to silt fence, Pond 1 will be utilized as a sediment basin for additional ' sediment control. See the Grading and Erosion Control Plan for locations of proposed erosion control measures. VII. WATER QUALITY 7.1 Porous Landscape Detention tThe 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 also 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. It was for these reasons that a porous landscape detention basin is proposed 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 t; of the 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 176 cubic feet is provided for the developed site. _ Page 3 i Drainage Design Considerations DMW Civil Engineers, Inc. t 637 Cowan Street November 5, 2003 IV. DEVELOPED CONDITIONS ' 4.1 Proposed Site Development Development of 637 Cowan Street will consist of construction of a new 3-unit, multi- family residence. The proposed site infrastructure includes onsite parking and ' utility services. ' 4.2 Developed Drainage Patterns The developed site has been divided into two (2) onsite drainage basins. Stormwater runoff will be conveyed overland to an onsite water quality area and ' allowed to infiltrate into the ground. Overflow from the water quality pond will flow into Cowan Street via a 2' metal sidewalk culvert. The peak 100-year developed discharge from the site will remain virtually unchanged from that which is outlined in the Old Town Masterplan. Runoff from Basin 1 (0.29 acres) drains overland to a water quality pond located ' just east of the existing building. Flows in excess of the water quality capture volume flow into Cowan Street. The peak 2 and 100-year flows from Basin 1 are 0.2 and 1.1 cfs respectively. Runoff from Basin 2 (0.08 acres) flows along the gutter of Cowan Street and combines with runoff from Basin 1. The peak 2 and 100-year flows for both basins are 0.4 and 1.4 cfs respectively. 4.3 Detention ' Onsite water quantity detention has not been provided for 637 Cowan Street. With an imperviousness value of 0.58, the site is only slightly less pervious that the 0.50 t used in the Old Town Masterplan. The difference in runoff coefficients results in an increase of runoff from the site of 0.1 and 0.4 cfs for the peak 2 and 100-year flows . respectively. Calculations are provided in Appendix B to illustrate the impact of additional flows. Due to site constraints, location and relatively small impact to the overall basin, a variance is being requested for a waiver of the onsite water quantity detention requirement. V. DESIGN CRITERIA 5.1 Design References Drainage design criteria specified in the Cityof 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. 5.2 Hydrologic Criteria The rational method has been used to estimate peak stormwater runoff from the project site. An initial 2-year and major 100-year design storms have been used to evaluate the proposed drainage system. Calculations made as part of this Page 2 Drainage Design Considerations for 637 Cowan Street Fort Collins, Colorado November 5, 2003 I. INTRODUCTION 1.1 Objective This study documents the results of a comprehensive hydrologic and hydraulic analysis of developed conditions for the proposed 637 Cowan Street development. The utility plans which accompany this report are entitled Final Construction Plans for 637 Cowan Street prepared by DMW Civil Engineers, Inc. 1.2 Proiect History and Previous Studies The proposed development is located at 637 Cowan Street. The site is within`the Old Town drainage basin but not within any regulatory floodplains. The City has no drainage study on file for this site. 1.3 Mapping and Surveying Field survey information and topographic mapping with a contour interval of 1-foot was obtained by DMW Civil Engineers from Cornerstone Land Surveying, Berthoud, Colorado. Additional topography outside of the project boundary was taken from City of Fort Collins Aerial Topography with a two (2) foot contour interval. II SITE LOCATION AND DESCRIPTION 2.1. Site Location The proposed development is located at 637 Cowan Street. The site is located in the northeast quarter of Section 13, Township 7 North, Range 69 West of the 6th Principal Meridian in the Town of Fort Collins, Colorado and is described as Part of Block 186, City of Fort Collins (See Vicinity Map). 2.2 Site Description The proposed development site is approximately 0.25 acres. The site has an existing single-family residence and detached garage. 111. HISTORIC CONDITIONS 3.1 Historic Drainage Patterns Stormwater runoff from 637 Cowan Street drains overland generally from west to east at slopes ranging from 0.5% to 1% toward the existing street. There is an existing low point immediately east of the existing house which retains some stormwater runoff. i Vicinity Map 637 Cowan Street - Fort Collins, Colorado 0 0 0 to M i5' iA O O O 7 M G TIMN0 S i ese ICE" ®°0° FEET 0 an t000 METERS PrmtedNomTOPOIWWOWildflowerPmdoctio (www.topo.00m) r Drainage Design Considerations for r 637 Cowan Street r EXHIBITS ' Exhibit 1 637 Cowan Street Drainage Plan APPENDICES 1 Appendix A: Hydrology Calculations Appendix B: Hydraulic Calculations Appendix C: Erosion Control Calculations Appendix D: Water Quality Calculations 1 1 M 1 1 1 r 1 Drainage Design Considerations for 637 Cowan Street TABLE OF CONTENTS VICINITY MAP Page No. I INTRODUCTION 1.1 Objective.................................................1 1.2 Project History and Previous Studies ............................. 1.3 Mapping and Surveying......................................1 1 II SITE LOCATION AND DESCRIPTION 2.1 Site Location..............................................1 2.2 Site Description............................................1 III HISTORIC CONDITIONS 3.1 Historic Drainage Patterns ..................................... 1 IV DEVELOPED CONDITIONS 4.1 Proposed Site Development .................... :............. 2 4.2 Developed Drainage Patterns ................................. 4.3 Detention Pond 1........................................... 2 2 V DESIGN CRITERIA 5.1 Design References.........................................2 5.2 Hydrologic Criteria .......................................... 2 5.3 Hydraulic Criteria ........................................... 3 - VI EROSION CONTROL 6.1 Erosion Control Plan and Criteria .............................. 3 VII WATER QUALITY, 7.1 Porous Landscape Detention ................................. 3 ' VIII CONCLUSIONS 8.1 'Compliance with Standards ................................... 4 REFERENCES..................................................4 �i 4 m`= ' CIVIL ENGINEERS ' November 5, 2003 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 1 43 5 WEST 29' STREET LOVELAND, CO BO53B (970) 461-2661 FAX (970) 461-2565 WWW.DMWCIVILENGINEERS.COM Re: Drainage Design Considerations for 637 Cowan Street Fort Collins, Colorado ' Dear Staff: DMW Civil Engineers is pleased to submit this drainage study for 637 Cowan Street for your review. This report complies with 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 CIVIL ENGINEERS Jade P. Miller, P.E. (CO #33885) key, Project Manager Drainage Design Considerations for 637 Cowan Street Fort Collins, Colorado November 5, 2003 Prepared for: Barry Schram PO Box 270887 Fort Collins, Colorado 80527 Prepared by: PM1/!EERS 1435 W. 29'° Street Loveland, Colorado 80538 Phone:(970)461-2661 Fax: (970)461-2665 Project Number: 0301.00-COW