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Home My WebLink AboutLIBERTY COMMON SCHOOL ADDITION - SITE PLAN ADVISORY REVIEW - 11-02 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTNo Text I I I 1 11 11 t I 1 o o z z a NUa O Hz mWwo i -� X4'z } WOQ � >o m W J F% a W I 3 s_ L W J W p H 'z Q M111�Y �0�� Wr Refrt IJi: OI�IfC Sw4 1'�tOW OYlyntl Bl YFI I I I I 1 1 I I 1 I 1 Exhibits L, Drainage Design Considerations Liberty Common School February 27, 2002 Davis, Miller & Wohnrade Civil Engineers, Inc. REFERENCES 1.) Storm Drainage Report for Vipont Manufacturing Facility, Stewart & Associates, August 1, 1988. 2.) Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, May, 1984. 3.) Drainage Criteria Manual, Volume 3, Urban Drainage and Flood Control District, Wright -McLaughlin Engineers, Denver, Colorado, March, 1969. Page 6 I Drainage Design Considerations Liberty Common School February 27, 2002 L Davis, Miller & Wohnrade Civil Engineers, Inc. VIII. CONCLUSIONS 8.1 Compliance with Standards ^ All drainage analyses have been performed according to the City of Fort Collins Storm Drainage Design Criteria Manual (SDDCM) and, the Urban Drainage and Flood Control District's Drainage Criteria Manual. No variances are requested „ as part of the proposed development. 8.2 Easements The Liberty Common School site drains to the Prospect Ponds Natural Area which is located east of the site. The Natural Area is owned by the City of Fort Collins and managed by the Natural Resources Department. The Natural p Resources Department has been contacted regarding the proposed gymnasium li addition. DMW is in the process of determining whether or not a drainage easement has P already been recorded in the vicinity of the Prospect Ponds Natural Area as part of the Prospect Industrial Park development. Virtually the entire Prospect Industrial Park development drains to the natural area and one would expect that li an easement has already been established. If this is the case, then an additional easement would not be required. aq Page 5 Drainage Design Considerations Liberty Common School February 27, 2002 Davis, Miller & Wohnrade Civil Engineers, Inc. 5.4 Detention Requirements Detention is not a requirement for the proposed development due to the proximity of the site to the Cache La Poudre River. 5.5 Street Capacity The street capacity of Sharp Point Drive has been determined based on design drawings for Prospect Industrial Park. The capacity of the street is based on the 2-year design storm and is estimated to be roughly 3.3 cfs. The 2-year peak discharge at Design Point 1, based on post -development conditions, is 2.9 cfs. The street capacity at Design Point 1 then, has not been exceeded. Appendix D contains calculations in support of this analysis. VI. EROSION CONTROL 6.1 Erosion Control Plan 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. A gravel inlet filter will be placed at the existing area inlet located west of the existing school. Temporary sediment control consisting of silt fencing will surround the area of the proposed gymnasium addition. VII. WATER QUALITY 7.1 Extended Detention The issue of water quality has been addressed for the Liberty Common School site. Runoff from the roof of the proposed gymnasium (0.43 acres) will be direct to an on -site water quality facility located adjacent to the gymnasium. Porous landscape extended detention will be used to treat stormwater runoff from the roof. A four(4)inch diameter PVC pipe will convey stormwater from the detention facility to March Court. A six(6)inch diameter pipe would have been preferable tl however, due to site constraints only a four(4)inch diameter pipe was feasible. Extended detention calculations can be found in Appendix E, and are based on Best Management Practices (BMP's) provided by the Urban Drainage and Flood Control District (UDFCD), Drainage Criteria Manual, Volume 3. I Page 4 C, Drainage Design Considerations Liberty Common School February 27, 2002 Davis, Miller & Wohnrade Civil Engineers, Inc. 4.2 Post -development Drainage Patterns The overall drainage pattern of the site will remain unchanged from pre to post - development conditions. Stormwater runoff from Basin 1 will drain overland to Sharp Point Drive and March Court as it has done historically. Basin 2 will continue to drain to the existing curb inlet and, Basin 3 will also follow the historic drainage pattern. 4.3 Post -development Drainage Basins The area of Basin 1 (4.6 acres) increased slightly compared to historic Basin H1 (4.5 acres.) The peak 2 and 100-year discharges at Design Point 1 are 2.9 and 13.0 cfs respectively (See Exhibit 3.) The area of Basin 2 (1.0 acres) has been reduced slightly compared to historic Basin H2 (1.1 acres.) Basin H3 will remain unchanged. V. DESIGN CONSIDERATIONS 5.1 Design References Drainage design criteria specified in both the City of Fort Collins Storm Drainage Design Criteria Manual,(SDDCM) and Storm Drainage Criteria Manual, Volume 3, by the Urban Drainage and Flood Control District have been referenced for this study. 5.2 Hydrologic Criteria The Rational Method has been used to estimate peak stormwater runoff from the developed site. The initial 2 and 10-year and, major 100-year design storms have been used in the evaluation of pre and post -development drainage conditions (See Appendix C.) Rainfall intensity data for the pre -development condition has been taken from the old intensity curves (Figure 3-1 of the SDDCM.) Rainfall intensity data for post -development conditions has been taken from the new rainfall intensity data ( Figure 3-1 b.) The time of concentration to Design Point 1 remained the same for both pre and post -development conditions. 5.3 Hydraulic Criteria The computer program "Flowmaster" has been used to analyze the capacity of the proposed PVC pipe which conveys stormwater from the extended detention facility to March Court. Page 3 Drainage Design Considerations Liberty Common School February 27, 2002 Davis, Miller & Wohnrade Civil Engineers, Inc. 2.3 Site Description Liberty Common School is located on Lot 8 of Prospect Park East P.U.D. and, Lots 1 , 2, 3, 6 and part of Lot 23 of Prospect Industrial Park. The site is approximately 7.76 acres and is partially developed with an existing building, driveway, parking lot and playground (See Exhibit 2). Lots 3 and 6 remain undeveloped at this time and may be used in the future as playing fields. III. PREDEVELOPMENT CONDITIONS 3.1 Major Drainage Basin The site is located in the Poudre River drainage basin and, partially in the Spring Creek drainage basin according to the City of Fort Collins stormwater basin map. 3.2 Pre -Development Drainage Basins The pre -developed site has been divided into three distinct drainage basins. The basin boundaries delineated by DMW are consistent with the boundaries on Sheet 8 of 8 from the 1988 report by Stewart (See Drawing 1). Basin H1 (4.5 acres) drains overland from northwest to southeast at a slope of 1.20% to Sharp Point Drive and March Court. Basin H1 includes both on and off -site areas draining to Design Point H1. Basin H2 (1.1 acres) drains to an existing four (4) foot curb inlet located west of the existing school. Stormwater is conveyed from the inlet thru a storm sewer to an existing pond located north of the project site. The roof of the existing building makes up the majority of Basin H3. Runoff from the roof is directed to the north to the existing pond mentioned previously. Stormwater runoff from all three basins is eventually routed to the Prospect Ponds Natural Area which is located to the east of the site. IV. POSTDEVELOPMENT CONDITIONS 4.1 Proposed Site Improvements Planned development for the Liberty Common School site includes the addition of a gymnasium. The area of the gymnasium roof is 18,918 sf (0.43 acres.) The area to be occupied by the proposed gymnasium is currently covered with asphalt and concrete sidewalks and,"a gravel playground. The overall imperviousness of the site will be increased due to the gymnasium addition. Page 2 I Drainage Design Considerations for Liberty Common School Fort Collins, Colorado February 27, 2002 Ul I. INTRODUCTION 1.1 Objective To provide documentation of a drainage evaluation for both pre and post - development conditions for the Liberty Common School site. Specific objectives as part of this study are: 1. To address the street capacity of Sharp Point Drive, at a design point located downstream of the project site, for both pre and post -development conditions; 2. To provide the design of an extended detention, water quality facility; 3. To consider any possible adverse effects downstream of the development due to developed stormwater. 1.2 Project History and Previous Studies The Liberty Common School site was formerly the Vipont manufacturing facility. A drainage report (Reference 1 and Appendix A) was prepared for the Vipont development in 1988 by Stewart & Associates. 1.3 Mapping and Surveying Aerial topographic mapping of the site at a two (2) foot contour interval was obtained from the City of Fort Collins Geologic Information System department r and is dated April, 1999. L. 1.4 Site Reconnaissance A site visit was conducted on February 11, 2002 by the project engineer. Based on the topographic mapping, existing drainage basins and land use were confirmed as well as existing structures. II. SITE LOCATION AND DESCRIPTION 2.1 Site Location The site is located in the NE Quarter of Section 20, Township 7 North, Range 68 West of the 6th Principal Meridian in Fort Collins, Colorado. The project is bounded by Sharp Point Drive on the east and East Prospect Road on the north. (See Vicinity Map). 2.2 Floodplain Based on the City of Fort Collins GIS information, the Liberty Common School is located outside of the regulatory floodplain of the Cache La Poudre River (See Exhibit 1.) The Flood Insurance Rate Map (FIRM) has also been referenced which confirms that the site is located outside of the Special Flood Hazard Area (See Appendix B.) Vicinity Ma - Liberty Common School —4 oiiasae�rn '�; - n K Legend Parcels .T Railroads 4 Street Centerines tRiver, O 44�, Streams, and Ditches w d� g _ ■ lakes and Water Bodies r" T City Limits D r- i n D � W�nC+ry L.m4s O i li IAap crczded with Arc IMS-Copyright] 198242M ESRllnc. 01777= Drainage Design Considerations for Liberty Common School EXHIBITS Exhibit 1 City of Fort Collins GIS Floodplain Mapping Exhibit 2 Pre -Development Drainage Plan Exhibit 3 Post -Development Drainage Plan APPENDICES Appendix A: Excerpts from the 1988 Vipont Drainage Report Appendix B: FIRM Floodplain Mapping Appendix C: Rational Method Runoff Calculations Appendix D: Street Capacity Calculations Appendix E: Extended Detention Calculations DRAWINGS Drawing 1 Sheet 8 of 8, from the Storm Drainage Report for Vipont Manufacturing Facility, Stewart & Associates, August 1, 1988. Drainage Design Considerations for Liberty Common School TABLE OF CONTENTS VICINITY MAP INTRODUCTION Page No. 1.1 Objective.......................................................................................... 1 1.2 Project History and Previous Studies .............................................. 1 1.3 Mapping and Surveying................................................................... 1 1.4 Site Reconnaissance....................................................................... 1 II SITE LOCATION AND DESCRIPTION 2.1 Site Location.................................................................................... 1 2.2 Floodplain........................................................................................ 1 2:3 Site Description............................................................................... 2 III PRE -DEVELOPMENT CONDITIONS 3.1 Major Drainage Basin...................................................................... 2 3.2 Pre -development Drainage Basins .................................................. 2 IV POST -DEVELOPMENT CONDITIONS 4.1 Proposed Site Improvements........................................................... 2 4.2 Post -development Drainage Patterns .............................................. 3 4.3 Post -development Drainage Basins ................................................ 3 V DESIGN CONSIDERATIONS 5.1 Design References.......................................................................... 3 5.2 Hydrologic Criteria............................................................................ 3 5.3 Hydraulic Criteria............................................................................ 3 5.4 Detention Requirements.................................................................. 4 5.5 Street Capacity ................................................................................ 4 VI EROSION CONTROL 6.1 Erosion Control Plan........................................................................ 4 VII WATER QUALITY 7.1 Extended Detention......................................................................... 4 Vill CONCLUSIONS 8.1 Compliance with Standards...............:............................................. 5 8.2 Easements....................................................................................... 5 REFERENCES........................................................................................... 6 DMW Davis, Miller * Wohnrade Give/ En sneers, Inc. 435 W. 97 Street, Loveland, Colorado 80538 9 Phone: 970-46 I -266 I ,Fax: 970-461 -2665 February 27, 2002 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: Liberty Common School Fort Collins, Colorado Project Number: 0203.00-LCS Dear Staff: Davis, Miller & Wohnrade Civil Engineers, Inc. (DMW) is pleased to submit this report for Liberty Common School for a Site Plan Advisory Review. This report was prepared in compliance with technical criteria set forth in the City of Fort Collins Storm Drainaoe Desian Criteria and Construction Standards manual. If you should have any questions or comments as you review this report, please feel free to contact me at your convenience. Sincerely, Davis, Miller & Wohnrade Civil Engineers, Inc. . v'J Mary B. Wohnrade;-P.E. Project Manager Drainage Design Considerations for Liberty Common School Fort Collins, Colorado February 27, 2002 Prepared for: Liberty Common School 1725 Sharp Point Drive Fort Collins, Colorado 80525 Prepared by: DMW Dav15, Miller t Wohnrade Civil lfngmeer5, Inc. 1435 W. 29' Street Loveland, Colorado 80535 Phone: (970)461-2GG 1, Fax: (970)46 I -2665 Project Number: 0203.00-LC5