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Home My WebLink AboutSWIFT ADDITION TO FOSSIL LAKE P.U.D. - COUNTY REFERRAL - 33-01(I) - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFinal Drainage Study Swift Addition to Fossil Lake P.U.D. July 20, 1999 Northern Engineering Services, Inc. REFERENCES 1). McClellands Basin Master Drainage Plan, City of Fort Collins, Colorado, Greenhome & O'Mara, Inc., June 20, 1986. 2.) Fossil Creek Drainage Basin Master Drainageway Planning Study, City of Fort Collins, Larimer County, Colorado, Simons, Li & Associates, Inc., August 1982. 3.) Larimer County Stormwater Management Manual, Resource Consultants Inc., Fort Collins, Colorado, April 1979. 4.) Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, May, 1984. 5.) Drainage Criteria Maunal, Volume 1-3, Urban Drainage and Flood Control District, Wright -McLaughlin Engineers, Denver, Colorado, March, 1969. P, Final Drainage Study Northern Engineering Services, Inc. Swift Addition to Fossil Lake P.U.D. ' July 20, 1999 The developer will design and construct all irrigation related facilities associated with this development. This Drainage Study and associated Utility Plans will not provide details of any irrigation related structure or facility. I I I I r 5 I I ['1 O Final Drainage Study Northern Engineering Services, Inc. Swift Addition to Fossil Lake P.U.D. July 20, 1999 7.2 Grass -Lined Swales Grass -lined swales will be used to collect overland flows from roadways, yards and parking lots. The swales will be used to limit the extent of directly connected impervious areas. VIII. EROSION CONTROL 8.1 Erosion Control Plan and Criteria Erosion control will be provided to control both rainfall and wind erosion. Evaluation of the rainfall erosion control plan will be completed first, with the wind erosion control plan to follow. The Erosion Control Reference Manual for Construction Sites (ECRM), City of Fort Collins, will be referenced for this erosion control plan which will be provided at final design. 8.2 Rainfall Erosion Control Plan The proposed rainfall erosion control plan during construction will consist of temporary structural erosion control measures. Gravel inlet filters will be placed at all curb inlets. Straw bale inlet protection will be placed at the upstream end of the outlet pipe from Pond 100. Vegetative erosion control will be used in association with this project by using straw mulch with temporary seeding. It will be clearly noted on the Final Grading, Drainage and Erosion Control Plan that no soils shall remain exposed for more than thirty days before requiring temporary or permanent erosion control measures, unless approved by Stormwater Utility. Performance standards for the City of Fort Collins will be used for "During Construction" activities. The "Construction Sequence" for the proposed development will be given on the Final Grading, Drainage and Erosion Control Plan. 8.3 Wind Erosion Control Plan The proposed wind erosion control plan during construction will consist of silt fencing. From the Wind Erodibility Map for Fort Collins, Colorado, the site is located in a moderate erodibility zone. The Final Grading, Drainage and Erosion Control Plan will identify locations of proposed erosion control measures. IX. CONCLUSIONS 9.1 Compliance with Standards All drainage analyses have been performed according to the Larimer County Stormwater Management Manual, the City of Fort Collins Storm Drainage Design Criteria Manual and the Urban Drainage and Flood Control District's Drainage Criteria Manual. There are no variances requested as part of the proposed development. 9.2 Irrigation Facilities Final Drainage Study Northern Engineering Services, Inc. Swift Addition to Fossil Lake P.U.D. July 20, 1999 V. HYDROLOGIC ANALYSIS 5.1 Design Criteria Modeling criteria contained in the Larimer County Stormwater Management Manual, (LCSMM, Reference 3), the City of Fort Collins Storm Drainage Design Criteria Manual (SDDCM, Reference 4) and Storm Drainage Criteria Manual by the Urban Drainage and Flood Control District (Reference 5) have been referenced for this Final Drainage Study. The Rational Method has been used to estimate peak stormwater runoff within the developed site for the initial 2-year and major 100-year design storms. Rainfall intensity data for the Rational Method has been taken from the City of Fort Collins Rainfall Intensity and Duration Frequency Curves (See Figure 3-1). 5.2 Developed Basins and Future Filings All storm drainage facilities for this development will be designed to accommodate future developed conditions, which will far exceed the maximum runoff from adjacent undeveloped basins. Consideration will be given to future development of adjacent filings which will impact the design of proposed inlets, swales, storm sewers and detention facilities. VI HYDRAULIC ANALYSIS 6.1 Design Criteria Modeling criteria contained in the Larimer County Stormwater Management Manual (Reference 3) the City of Fort Collins Storm Drainage Design Criteria Manual, (SDDCM, Reference 4) and Storm Drainage Criteria Manual by the Urban Drainage and Flood Control District (Reference 5) will be referenced for the Final Drainage Study. In addition to the aforementioned criteria manuals, the following four computer programs will be used in the design of inlets, swales, culverts and storm sewers: 1) "UDINLET" has been used in the design of inlets; 2) "Flowmaster" has been used in the design of all swales; 3) "HY8" has been used in the design of all culverts; 4) "Storm Sewer Module", by Eagle Point software has been used in the design of all storm sewers. VH. WATER QUALITY 7.1 Design Intent and Criteria Water quality measures will be implemented for the proposed development and will include extended detention and grass -lined swales. Pond 100 will be designed with a longer than usual drain time, from 12 hours to a 40 hour drain time, for further water quality enhancement. Criteria contained in the Urban Storm Drainage Criteria Manual Volume 3-Best Management Practices (Reference 5) will be used in the design of all water quality facilities. Final Drainage Study Swift Addition to Fossil Lake P.U.D. July 20, 1999 Northern Engineering Services, Inc. drains to the Fossil Creek Reservoir. This ditch will remain in service. M. HISTORIC CONDITIONS 3.1 Maior Drainage Basin The site lies entirely in the Fossil Creek Reservoir major drainage basin (see Historic Plan). Basin HI is roughly 55.0 acres (See Exhibit). According to the Fossil Creek Drainage Basin Master DraiMeway Planning Study (Reference 2), detention is not a requirement in the Fossil Creek Basin. 3.2 Historic Drainage Patterns Basin Hl slopes from the north to the south at slopes ranging from 0.7 to 3.0% towards Fossil Lake Reservoir.. The 2 and 100-year discharges from this basin are 11.4 and 51.6 cfs respectively. 3.3 Off -Site Flows Off -site runoff enters the Swift Addition to Fossil Lake P.U.D. site from the west from Basin OS 1 (see Historic Exhibit). The anticipated 2 and 100-year discharges from this basin are ' 6.7 and 29.1 cfs respectively. The proposed improvements to the site will intercept and route runoff from Basin OS south to Fossil Creek Reservoir. IV. DEVELOPED DRAINAGE 4.1 Proposed Development The Swift Addition to Fossil Lake Village P.U.D. development consists of one filing and is proposed as one phase. The proposed development includes residential lots. Tracts and Outlots will be provided for open space parks and landscape areas. The open space area identified as Outlot D will also serve as stormwater quality area. This area will convey stormwater through a grass lined Swale to the water quality pond to the south of the site. 4.2 Development Drainage Basins Stormwater runoff from the proposed development will be routed to an off -site water quality facility via overland flow, storm sewers and swales. Basins 10-30, a total of 50.9 acres, will be routed to Pond 100 for water quality treatment. Pond 100 will release to the south to the Fossil Creek Reservoir. Basin 40, a total of 3.8 acres, will be released undetained to the McClelland's Drainageway. The anticipated 2 and 100-year discharges from this basin are 1.7 and 7.6 cfs respectively With the final drainage study we will provide calculations that show this small release will have no impact on the peak flow in the McClellands drainageway during a storm event. Preliminary Drainage Study for Swift Addition to Fossil Lake P.U.D. First Filing Fort Collins, Colorado July 19, 1999 I. INTRODUCTION 1.1 Objective This report summarizes a preliminary hydrologic and hydraulic analysis of both existing and developed conditions for the Swift Addition to Fossil Lake P.U.D. residential development, based on design criteria adopted by Larimer County and the City of Fort Collins, Colorado. 1.2 Mapping and Surveying Aerial topographic mapping with a contour interval of one (1) foot was used in conjunction with field survey information, which was provided by King Surveyors of Windsor, Colorado. 1.3 Site Reconnaissance ' A site visit was conducted on July 1, 1999 by the project engineer. Based on the topographic mapping, existing drainage basins and land use were confirmed as well as existing structures and utilities. The location and dimensions of existing storm drainage facilities were ' verified as well as their condition and flow direction. J '1 i I I II. SITE LOCATION AND DESCRIPTION 2.1 Site Location The Swift Addition to Fossil Lake P.U.D. is located in the east Half of Section 9, Township 6 North, Range 68 West of the Third Principal Meridian in Larimer County, Colorado (see Vicinity Map). The site is bounded by The Fossil Lake PUD on the west, County Road 36 on the north and County Road 7 on the east.(See vicinity map) 2.2 Existing Site Description The Swift Addition to Fossil Lake P.U.D. site is an approximately 55 acre agricultural parcel. The site slopes generally from northwest to southeast at slopes ranging from 0.7% to 3.0%, towards Fossil Creek Reservoir. There are no existing residences on the site. 2.3 Irrigation Ditches and Reservoirs There are two existing irrigation ditches located on or adjacent to the site, Muskrat Ditch and Mail Creek Ditch. Muskrat Ditch is located at the north end of the site and flows from west to east. The improvements proposed as part of the First Filing will not interfere with this concrete lined ditch. Mail Creek Ditch flows along the west property line of the site from north to south and 1 TABLE OF CONTENTS Page I. INTRODUCTION 1.1 Objective............................................................................................... 1 1.2 Mapping and Surveying........................................................................ 1 1.3 Site Reconnaissance ............................................................................. I II. SITE LOCATION AND DESCRIPTION 2.1 Site Location......................................................................................... 1 2.2 Existing Site Description....................................................................... 1 2.3 Irrigation Ditches and Reservoirs.......................................................... 1 III. HISTORIC CONDITIONS 3.1 Major Basin Description....................................................................... 2 3.2 Historic Drainage Patterns.................................................................... 2 3.3 Off -Site Flows....................................................................................... 2 IV. DEVELOPED DRAINAGE 4.1 Proposed Development......................................................................... 2 4.2 Developed Drainage Basins................................................................... 2 V. HYDROLOGIC ANALYSIS 5.1 Design Criteria...................................................................................... 3 5.2 Developed Basins and Future Filings .................................................... 3 VI. HYDRAULIC ANALYSIS 6.1 Design Criteria..................................................................................... 3 VII. WATER QUALITY 7.1 Design Intent and Criteria.................................................................... 3 7.2 Grass -Lined Swales................................................................................ 4 VIR. EROSION CONTROL 8.1 Erosion Control Plan and Criteria......................................................... 4 8.2 Rainfall Erosion Control Plan ............................................................... 4 8.3 Wind Erosion Control Plan .................................................................. 4 IX. CONCLUSIONS 9.1 Compliance with Standards.................................................................. 4 9.2 Irrigation Facilities................................................................................ 5 REFERENCES................................................................................................... 6 B6' L z " SITE , j. ;�, : I o M?ft CREKK Da f _• cB7627 sl .. IN 4917 FossdCrerkP. D. ,! ' .. •10 Fossil Greek i 4865Aft rs NJ) AApo 17 16 a S'+ncdc Luke - Duck Lake r fa9n ✓ \ 161997 WddBowa Pioductims (www.tcPo.com) 1 A --I — rJ „ r O R T H E R N N E N G I N E E R I N G SERVICES INC July 20, 1999 f Larimer County Engineering Department P.O. Box 1190 Fort Collins, Colorado 80522 RE: Swift Addition to Fossil Lake P.U.D. iLarimer County, Colorado iDear Staff: Northern Engineering Services, Inc. is pleased to submit this Preliminary Drainage Study for the Swift Addition to Fossil Lake P.U.D. for your review. This report was prepared in compliance with technical criteria contained in the Larimer County Stormwater Management Manual and the City of Fort Collins, Storm Drainage Design I Criteria and Construction Standards Manual. If you should have any questions or comments as you review this report, please feel free ito contact me at your convenience. Sincerely, NORTHERN ENGINEERING SERVICES, INC. George Schock Project Manager 420. SOUTH HOWES, SUITE 202, FORT COLLINS, COLORADO 80521, (970) 221-4158, FAX (970) 221.4159 Preliminary Drainage Study for Swift Addition to Fossil Lake P.U.D. Fort Collins, Colorado July 20, 1999 Prepared For: The Everitt Companies Fort Collins, Colorado 80525 Project Number: SWF 9925.00 Prepared By: Norihem Engineering Services, Inc 420 S. Howes. Suite 202 Fort Collins, Colorado 80521 Phone: (970)2214158