The URL can be used to link to this page

Home My WebLink About800, 808 & 814 W. PROSPECT RD. MIXED-USE (OBSERVATORY PARK) - PDP - 41-02A - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT (3)Drainage Design Considerations Frazier Subdivision April28, 2004 DMW Civil Engineers The proposed rainfall erosion control plan during construction will consist of temporary structural erosion control measures. Temporary sediment control consisting ofsiltfencing will surround areas of the proposed construction. Avehicle tracking area will be used during construction as well as a straw bale barrier at the northeast corner of the site. See the' Grading and Erosion Control Plan for locations of proposed erosion control measures. In addition to silt fence, Detention Pond 1 will be utilized as a sediment basin for additional sediment control during construction. Erosion Control calculations are included in Appendix G. 5.5 Water Quality Structural Best Management Practices (BMPs) are proposed for the Frazier Subdivision site to improve water quality of runoff as recommended by the Urban Storm Drainage Criteria Manual. The detention pond incorporates an extended detention basin for water quality purposes. An extended detention basin (EDB) is a sedimentation basin which uses a much smaller outlet that extends the emptying time of the more frequently occurring runoff events to facilitate pollutant removal. Soluble pollutant removal can be somewhat enhanced by providing a small wetland marsh or ponding area in the basin's bottom to promote biological uptake. The basins are considered to be "dry" because they are designed not to have a significant permanent pool of water remaining between storm runoff events. However, EDB may develop wetlandvegetation and sometimes shallow pools in the bottom portions of the facilities. Pond 1 has been designed to provide 2500 cubic feet (0.06 ac-ft) of water quality capture volume in addition to 500 cubic feet (0.01 ac ft) of sediment storage with a water surface elevation of 5022.22. Release of the captured water is controlled by a steel plate with one column of five (5) 0.5625" (9/16") diameter circular perforations. For detention calculation purposes, this volume has been added to the 100-year storage requirements. Water quality calculations are included in Appendix E. VI. CONCLUSIONS 6.1 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. Page 5 Drainage Design Considerations DMW Civil Engineers Frazier Subdivision April28, 2004 Basin 3 (0.15 acres) consists of parking area and landscaping to the west of the proposed building. Basin 3 drains overland to a low point in the southwest corner of the parking area. Runoff is conveyed through a curb cut to an 18" culvert which outlets into Detention Pond 1. Calculations for the curb opening and storm pipe capacity are attached in Appendix B. The peak 2 and 100-year_flows from Basin 3 are 0.3 and 1.5 cfs respectively. ■ Basin 4 (0.46 acres) consists of the proposed building roof and Detention Pond 1. Runoff from Basin 4 (0.46 acres) drains overland and in roof drains directly into Detention Pond 1. The peak 2 and 100-year flows from Basin 4 are 0.8 and 3.4 cfs respectively. The peak 2 and 100-year flows into Detention Pond 1 from Basins 2, 3 and 4 are 2.4 and 10.0 cfs respectively. Basin 5 (0.31 acres) is comprised entirely of the northern portion of West Prospect Road and Right -of -Way that is adjacent to the site. Runoff from Basin 5 drains overland to the northern curb and gutter on Prospect. The peak 2 and 100-year flows from Basin are'0.5 and 2.1 cfs respectively. It is not possible for stormwater runoff from this basin to enter Detention Pond 1. 5.3 Detention The outlet to Detention Pond 1 is located at the southeast corner of the Frazier Subdivision site. Detention volume is utilized in two hydraulically connected areas. The first portion of Detention Pond 1 is located along the southern edge of the Frazier Subdivision site between West Prospect Road and the proposed building. As stormwater is detained, Detention Pond 1 expands to the north via the 24" storm pipe and encompasses the landscape area east of the parking area as well as part of the parking area north of the proposed building. Detention in the parking area is less than 18 inches deep and the 24" storm pipe is adequately sized to allow the two detention areas to behave as a single pond. The pond will utilize a single stage release consisting of a 3" high by 7" wide rectangular orifice. In addition to water quality containment volume, Detention Pond 1 provides 10675 cubic feet (ac-ft) of volume to detain the peak 100-year developed discharge from the site and release it at the historic 2-year rate. The maximum 100-year release from Pond 1 is 1.5 cfs with an associated water surface elevation of 5023.22. Detention pond calculations are included in Appendix C. 5.4 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. Page 4 Drainage Design Considerations DMW Civil Engineers Frazier Subdivision April28, 2004 4.3 Hydraulic Criteria The computer program "Flowmaster" has been used to analyze the capacity of proposed pipes and chases for the site. Also, custom spreadsheets as well as the computer program "Watershed Modeling Module" by Eagle Point Software has been used in the design of proposed detention ponds. V. DRAINAGE FACILITIES DESIGN 5.1 Proposed Site Development Development of the Frazier Subdivision site will consist of demolition of the existing buildings and construction of a new 3 story, 94 unit, multi -family apartment building. The proposed site infrastructure includes a parking lot, new utility services, and stormwater facilities. 5.2 Developed Drainage Patterns The developed site has been divided into five (5) onsite drainage basins. Stormwater runoff will be conveyed overland to an onsite detention and water quality pond and released into West Prospect Road. The peak 100-year developed discharge from the new impervious area added to the site will be released at a historic 2-year rate. Basin 01 (0.37 acres) is an offsite basin made up single family residences. Runoff �. from Basin 01 drains overland and enters Basin 1 on the westerly portion of Frazier Subdivision. The peak 2 and 100-yr flow are 0.3 and 1.3 cfs respectively. Basin 1 (0.05 acres) is comprised of a small landscape area on the northern and western portions of the site. Runoff from Basins 1 and 01 drains overland and through concrete pans to a sidewalk chase which discharges offsite. Offsite flows from Basin 01 are conveyed through Basin 1 to maintain historic flow patterns. The peak 2 and 100-year flows from Basins 01 and 1are 0.3 and 1.3 cfs respectively. No flows from these basins enter Detention Pond 1. Basin 2 (0.78 acres) consists of the parking area and landscape islands north of the proposed building. Basin 2 drains overland and in curbs and gutters to a low point on the east edge of the parking area. Stormwater runoff then travels to a 24" storm pipe via a curb opening and concrete pan. This storm pipe carries the runoff to Detention Pond 1. Calculations for the curb opening and storm pipe capacity are attached in Appendix B. In the 100-yr storm event this pipe will back up and the landscape island as well as a part of the parking lot will become part of the required storage for Detention Pond 1. The 100-yr WSEL for Detention Pond 1 is shown on the drainage plan. The peak 2 and 100-year inflows to Detention Pond 1 from Basin 2 are 1.6 and 6.2 cfs respectively Page 3 Drainage Design Considerations DMW Civil Engineers Frazier Subdivision 02 April28, 2004 - III. DRAINAGE BASINS AND SUB -BASINS 3.1 Major Basin Description The Frazier Subdivision site is within the Spring Creek Drainage Basin as identified by the City of Fort Collins Master Drainage Plan but not within any regulatory floodplains designated by either the City or FEMA. 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 Frazier Subdivision site historically drains overland to two separate basins. The northern portion of the site drains from southwest to northeast at slopes ranging from 1 % to 5%. These flows continue northeast from the site where they eventually enter Lake Street. The southern portion of the site drains from northwest to southeast at slopes ranging from 2%-14%. These flows travel overland onto West Prospect Road where they are conveyed downstream to the east in roadway gutters. IV. DRAINAGE DESIGN CRITERIA 4.1 Design Criteria and Restraints 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 2-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 3-1a). 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. Page 2 FI Final Drainage Report for Frazier Subdivision Fort Collins, Colorado April 28, 2004 I. INTRODUCTION 1.1 Objective This study documents the results of a comprehensive hydrologic and hydraulic analysis of both historic and post -development conditions for the proposed Frazier Subdivision development. The construction plans which accompany this report are entitled Final Construction Plans for Frazier Subdivision prepared by DMW Civil Engineers. 1.2 Project History and Previous Studies The Frazier Subdivision site was originally constructed as three single family residences and there are no existing drainage studies for the site other than the City of Fort Collins Master Plan. 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 Stuart & Associates, Fort Collins, Colorado. Additional topography outside of the project boundary was taken from City of Fort Collins Aerial Topography with, a two (2) foot contour interval. 1.4 Site Reconnaissance The project engineer performed a site visit to the Frazier Subdivision site in Fort Collins in February, 2004. Existing drainage patterns and structures were observed for use in defining drainage basin boundaries and flow patterns. II GENERAL LOCATION AND DESCRIPTION 2.1 Site Location The site is located in the southwest quarter of Section 14, Township 7 North, Range 69 West of the 6th Principal Meridian in the City of Fort Collins, Colorado. The site is bounded by Prospect Road on the south, and residential properties to the west, north and east (See Vicinity Map). 2.2 Site Description The Frazier Subdivision site is approximately 1.56 acres of developed land. The site is situated on three existing residential lots: 800, 808 and 814 West Prospect Road. There are several small buildings existing on the site and vegetation consists of grasses, planting beds, shrubs and trees. The site is zoned H-M-N (High Density Mixed -Use Neighborhood District) and is surrounded with existing single family and multi family housing. �r i i i i i 08 v,,spe ad - ia!'omn,oraca' i i i i i i i 105-07.000, W 105-06.000, W 1O5._CROOO' W WGS64 1O5RO4.00O' W �E r• NLt.M. Grand,le J " r' �.J '^>fy` Mtlan f(> ✓ s�.r + r• '� • `,^ f�� r '; •-�•L' Z - • Mums n LrL� ,!i I Golf CO.'se �' - _ 1 • V-� - [ri .0 . • i _ _ FORT sf •. ., jw..•c_�:.• - ��.i�9•� •C ...•� iIk! al 9FRRY IA _ MNy�£ebv ` C MI 1 �^ • D • �. ... t _77— lip s y/ czt A, ,55E ' TL y RAM sr •s .b -'iG �_ a `3a3ii• �' S �; r .>: - 1 �`Lt ._l'REJRNSIN i'' ��y' o r• _ ccoencT� sr .......... -. > T` L :1i .rLii� `'.._ rn Yr Y1==1 _ �_Sch S -r• R ��...:... .. _ ... 4t�` j"\_�; .4'a111 ` t 'cam`".":---• '.L — Pep r !`. ' + '�\ S �L tR• 1' -_. �111 wr.�. _: N rh 4h • YLi1. 11 3 f l soli m ��' 11 �•'�..f •, , • . . :` .• •�ti..iF"y v.UEoceL �i� '_ y i# 1..cIn�l�1 L•.L. y4Sf •+tP1F But. 0 Jill if IL 21 A� jl ` i ' �..'�) /Y/ �- wR<rt= �aRUA•= i �`L<)�. —_ DAARF ROAD t •_ A. s 1O50O7.00O' W 1O50O6.00O' W 1O5005.00O, W WGS64 105004,000' W I#,,,,,, o s i MtE 30°", �mI°°°IEEI fl _ _ :�0 = =1000 METE Printed fr=TOP0! ®2000 Wildflower Productions (www.topo Mm) Final Drainage Report for Frazier Subdivision EXHIBITS Exhibit•1 Frazier Subdivision Historic Drainage Plan Exhibit 2 Frazier Subdivision Developed Drainage Plan APPENDICES Appendix A Hydrology Calculations Appendix B Hydraulic Calculations Appendix C Detention Pond Calculations Appendix D Water Quality Calculations Final Drainage Report for Frazier Subdivision TABLE OF CONTENTS Page No. -1 INTRODUCTION 1.1 Objective .................................................1 1.2 Project History and Previous Studies ............................ 1 1.3 Mapping and Surveying ...................................... 1 1.4 Site Reconnaissance ........................................1 11 SITE LOCATION AND DESCRIPTION 2.1 Site Location ..............................................1 2.2 Site Description ............................................1 III DRAINAGE BASINS AND SUB -BASINS 3.1 Major Basin Description ...................................... 2 3.2 Sub -Basin Description ....................................... 2 IV DRAINAGE DESIGN CRITERIA 4.1 Design Criteria and Constraints ................................ 2 4.2 Hydrologic Criteria .......................................... 2 4.3 Hydraulic Criteria ........................................... 3 V DRAINAGE FACILITIES DESIGN 5.1 Proposed Site Development .................................. 3 5.2 Developed Drainage Patterns ................................. 3 5.3 Detention .................................................4 5.4 Erosion Control ............................................ 4 5.5 Water Quality .............................................. 5 VI CONCLUSIONS 6.1 Compliance with Standards ................................... 5 REFERENCES ..................................................6 I r ICIVIL ENGINEERS April 28, 2004 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 . Re: Final Drainage Report for Frazier Subdivision Fort Collins, Colorado Dear Staff: 1435 WEST 29" STREET LovELAND, CO 60536 (970) 461-2661 FAX (970) 461-2665 WWW.DMWCIVIL-ENOINEERS.COM DMW Civil Engineers is pleased to submit this drainage study for Frazier Subdivision for your review. This report complies with technical criteria set forth in the City of Fort Collins' Storm Drainaae 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 conformancewith 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 U• 33 85 ' (FOR REVIEW PURPOSES ONLY) SS/ONAL��`~ i Jade P. Miller, P.E. (CO #33885) Project Engineer �s. Final Drainage Report for Frazier Subdivision Fort Collins, Colorado April 28, 2004 Prepared for: Mr. Kevin Frazier Frazier and Company Ventures, LLC 141 South College Avenue, Suite 103 Fort Collins; CO 80524 Prepared by: pm"6beool 1435 W. 291' Street Loveland, Colorado 80538 Phone: (970)461-2661 Fax: (970)461-2665 Project Number: 0403.00-FRZ