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Home My WebLink AboutLEMAY AVENUE ESTATES - FDP - 37-04B - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFinal Drainage Report Lemay Avenue Estates June 29, 2005 Northern Engineering Services, Inc. REFERENCES 1) Drainage Criteria Manual, Urban Drainage and Flood Control District, Wright Water Engineers, Inc., Denver, Colorado, Updated June 2001. 2) Erosion Control Reference Manual for Construction Sites, City of Fort Collins, Colorado, Hydrodynamics, Inc., January 1991. 3) Fossil Creek Drainage Basin Master Drainageway Planning Study, City of Fort Collins, Larimer County, Colorado, Simons, Li & Associates, Inc., August, 1982. 4) Storm Drainage Design Criteria and Construction Standards, City of Fort Collins, Colorado, Updated April 1999. Page 6 I 7 7 7 7 Final Drainage Report Northern Engineering Services, Inc. Lemay Avenue Estates June 29, 2005 Drainage and Flood Control District (September 1999). A steel orifice plate with vertical perforations will be built into the outlet structures of these ponds to control the water quality capture volume as shown on the construction drawings for the development. VI. EROSION CONTROL PLAN 6.1 Erosion Control Criteria The erosion control plan presented here is intended to control both wind and rainfall erosion. The Erosion Control Reference Manual for Construction Sites (ECRM), City of Fort Collins, has been referenced for this erosion control plan. 6.2 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 (including Type R and Combination). Sediment traps will be placed at all pond outlet structures. Straw bales will be placed in swales at an interval of no less than 200 feet. Silt fencing will be installed at the locations shown on the Grading and Erosion Control Plan. Vegetative erosion control consisting of straw mulch with temporary seeding will be used on all open space areas that are disturbed with this project. All temporary erosion control structures are to remain in place until permanent vegetation has been established. The proposed erosion control plan after construction will consist of permanent riprap, which will be provided at the locations specified on the construction plans. All open space areas and grass -lined swales will be seeded with seed mixtures as specified in the planset. VH. CONCLUSIONS 7.1 Compliance with Standards All drainage design considerations are in accordance with the City of Fort Collins Storm Drainage Design Criteria Manual and the Urban Drainage and Flood Control District's Drainage Criteria Manual. Additionally, drainage stipulations outlined in previous drainage studies and master plans for the area have been strictly followed. Off -site stormwater will be safely routed around the site without being detained. Overall, the drainage system proposed within this report and the supporting construction documents provides adequate conveyance, detention and water quality enhancement for the developed stormwater runoff from the proposed development. Every attempt has been made to minimize any negative impacts on the downstream receiving waters. Page 5 ' Final Drainage Report Northern Engineering Services, Inc. Lemay Avenue Estates June 29, 2005 • The computer program "F1owMaster v6.1 [614o]" by Haestad Methods has been I used to analyze swales and major storm street capacities. • The Excel spreadsheet "UD Inlet vl.06a" by Urban Drainage and Flood Control District has been used to analyze inlet sizes. • An Excel spreadsheet based on Urban Drainage and Flood Control Street Capacity equations has been used to analyze street capacities. ' 4.5 Detention The primary function of the proposed detention ponds is to control release from the overall site such that the maximum allowable release from the historic 2-year storm is observed. Ponds 302, 303, 304 and 305 will also be utilized to provide water quality capture volume in their lower stage. I I 7 Pond 301 will discharge into a pipe which will daylight at Pond 302. Pond 302 will discharge into Stanton Creek. The release rate from Pond 302 was determined based on the 2-year release from historic basin EX-1 of 7.46 cfs. Since developed basins F1 and G2 flow into Stanton Creek undetained, the difference between developed 100-year flows and historic 2-year flows were subtracted from the 7.46 cfs. Also, the release from Pond 303 was subtracted from the 7.46 cfs, leaving Pond 302 with an allowable release rate of 1.0 cfs. Table 2, below summarizes detention pond peak discharges and detention volumes: TABLE 2 Detention Storage Summary Maximum Maximum 100-year Detention Discharge Volume Pond (cfs) (ac-ft) 301 5.00 6.30 302 1.00 3.80 303 0.50 0.09 304 0.20 0.33 305 0.14 2.30 Each pond will be controlled by an orifice plate to limit the peak discharge. Additionally, a water quality capture volume will. be provided at the bottom of the surface detention Ponds 302, 303, 304 and 305. An outlet box with vertical perforations will control the water quality volume. V. WATER QUALITY 5.1 Water Quality Measures and Criteria The primary water quality method will be built into Detention Ponds 302, 303, 304, and 305. Water quality capture volume (WQCV) will be provided in these ponds in order to remove sediment and other pollutants from developed runoff. Design of these ponds has been based on criteria for a 40-hour dry extended detention basin outlined in the Urban Storm Drainage Criteria Manual, Volume 3 — Best Management Practices by the Urban 7 Page 4 Final Drainage Report Northern Engineering Services, Inc. Lemay Avenue Estates June 29, 2005 IV. POST -DEVELOPMENT CONDITIONS 4.1 Post -development Conditions The proposed development will include the following: • residential lots for single family homes • on -site and off -site roadway improvements • drainage and utility improvements Developed drainage patterns will generally follow historic flow paths with drainage traveling from west to east into Stanton Creek. Five detention ponds will be provided on - site to intercept drainage and release discharge at the historical 2-year rate. Detention Ponds 301 and 302 were sized using the computer program SWMM (See Appendix D). Detention Ponds 303, 304, and 305 were sized using the FAA Method (See Appendix Q. I There will be two outfalls into Stanton Creek, one from Pond 302 and one from Pond 303. I 1 The site hydrology was completed using a Rational C-value of 0.95 for developed areas with asphalt, concrete, or roof material. A C-value of 0.50 was used for gravel areas. A C-value of 0.15 was used for lawns and landscaped areas, assuming a sandy soil value, based on NRCS soil mapping of the site. The majority of lots are graded so that drainage will be directed to the street or backyard swale. The streets are graded to low points that will discharge into the detention ponds on -site. Additional on -grade inlets have been provided to intercept roadway drainage and discharge into Pond 301. 4.2 Design Criteria and References Drainage criteria outlined in both the City of Fort Collins Storm Drainage Design Criteria Manual, (SDDCM) and the Urban Storm Drainage Criteria Manual (USDCM) by the Urban Drainage and Flood Control District have been referenced for this study. 4.3 Hydrologic Criteria . The Rational Method has been used to estimate peak stormwater runoff within the developed site. The minor 2-year and major 100-year design storms have been used in the design of the proposed drainage system, which includes inlets, storm sewer, and surface detention. The FAA Method has been used to size Detention Ponds 303, 304, and 305. The computer program "UDSWMM2000" by Urban Drainage and Flood Control District has been used to size the Detention Ponds 301 and 302. Rainfall intensity data for the Rational Method and the FAA Method has been taken from Figure 3-la updated by the City of Fort Collins in 1999. Rainfall data for SWMM has been taken from Figure 3-1c, also updated by the City of Fort Collins in 1999. 4.4 Hydraulic Criteria The following computer programs have been used in the proposed design of the storm systems for the site at final design: • The computer program "Hydraflow" by Intelisolve has been used to design and analyze the storm sewer lines and outlet pipes in final design. 1 Page 3 i �oo I Final Drainage Report Lemay Avenue Estates June 29, 2005 Northern Engineering Services, Inc. a sanitary sewer line owned by South Fort Collins Sanitation District. An existing drainage easement for Stanton Creek lies adjacent to the eastern property line also. Existing gas, telephone, overhead utility, fiber optic and irrigation lines run along the western edge of the site in the Lemay Avenue right-of-way. III. PRE -DEVELOPMENT CONDITIONS 3.1 Major Basin Description The site is located in the Fossil Creek Drainage Basin, which has recently been revised by the City of Fort Collins. New detention requirements in this basin now restrict the 100- year developed release rate to the 2-year historic rate. The portion of Stanton Creek that runs adjacent to the project site is included in the modeling for the Fossil Creek Drainageway Planning Study (Study Reach 25). The proposed development will be entirely out of the floodplain boundary and erosion buffer for Stanton Creek; therefore, there are no floodplain considerations for this development. 3.2 Pre -development Drainage Patterns The site drains generally from west to east, at slopes ranging from 1.0% to 6.0%, towards Stanton Creek. Slopes directly adjacent to Stanton Creek range from 4:1 to 2.3:1, with the creek running south to north at slopes ranging from 0.4% to 2.2%. Runoff from the existing single-family residence currently flows to the irrigation ditch surrounding the house. This area was not included in the historic calculations, but will be included in the proposed improvements for the site. A historic drainage exhibit along with a Rational Method analysis is included with this study. The results of hydrologic estimates and hydraulic analyses are summarized in Table 1. TABLE 1 Historic Drainaoe Outfalls Maximum 2-year Release Area Peak Flow Rate Location (Acres) (cfs) (cfs/ac) Existing undeveloped field 43.33 7.46 0.17 Off -site drainage from the north has historically been intercepted in a drainage swale that runs along the northern edge of the site and discharges directly into Stanton Creek. Drainage from the northeastern portion of Lemay Avenue runs in a roadside swale to the north. Drainage from the southeastern portion of Lemay runs in a roadside swale that discharges to the south. The 100-year floodplain boundary for Stanton Creek has been shown on the drainage exhibit for the project, and will not be altered by this development. The proposed site plan for Lemay Avenue Estates is entirely out of the floodplain boundary and erosion buffer. Release from the detention ponds on -site will be allowed at the bottom of the creek bed. Stanton Creek is dry for the majority of the year, with seasonal releases. Stanton Creek historically flows to Fossil Creek, which ultimately discharges into Fossil Creek Reservoir located east of the site. 7 Page 2 Final Drainage Report Lemay Avenue Estates June 29, 2005 Final Drainage Report for Lemay Avenue Estates Fort Collins, Colorado June 29, 2005 I. INTRODUCTION 1.1 Obiective Northern Engineering Services, Inc. This report summarizes the results of a comprehensive analysis of both pre- and post - development hydrologic and hydraulic conditions for the Lemay Avenue Estates site in Fort Collins, Colorado. Specifically, this report will serve the following: • Preserve existing drainage release rates and patterns for the site • Minimize any adverse effects downstream of the project due to the developed conditions 1.2 Mapping and Surve dung The initial land survey of the project site was provided by King Surveyors Incorporated; Windsor, Colorado. The survey was performed in July of 2004. The existing topography was given at a one -foot contour interval. Additionally, existing structures, roadways, utilities, etc. were also provided. All vertical elevations have been referenced to City of Fort Collins Benchmark 7-96 located at the southwest corner of Lemay Avenue and Province Drive (elevation = 4959.34, NGVD 1929). Horizontal locations have been referenced from Colorado State Plane Coordinates NAD 83 (1992) datum. 1.3 Site Reconnaissance Several site visits have been conducted by Northern Engineering Services, Inc.. Existing drainage patterns and land use were among the items confirmed during these visits. IL SITE LOCATION AND DESCRIPTION 2.1 Site Location The project site is located south of East Trilby Road and east of South Lemay Avenue in Fort Collins, Colorado. More specifically, the site is located in the northwest corner of the southwestem quarter of Section .18, Township 6 North, Range 68 West of the 6`h Principal Meridian in the City of Fort Collins, County of Larimer, State of Colorado. The project is bounded to the north by Stanton Creek Subdivision (Second Filing), to the east by Greenstone P.U.D., to the south by a single-family residence, and to the west by Lemay Avenue (See Vicinity Map — Appendix A). 2.2 Site Description The project site is approximately 48.47 acres and has historically been a single-family residence and undeveloped alfalfa field. The existing home and garage are located in the westem-central portion of the site. The site soils are primarily loam, and are classified as Hydrologic Group B by the Natural Resources Conservation Service (Loveland Quadrangle). A 20'easement intersects the eastern property boundary at several locations and contains Page I Table of Contents VICINITY MAP Page I. INTRODUCTION 1.1 Objective.......................................................................................... 1 1.2 Mapping and Surveying................................................................... 1 1.3 Site Reconnaissance......................................................................... 1 U. SITE LOCATION AND DESCRIPTION 2.1 Site Location.................................................................................... 1 2.2 Site Description................................................................................. 1 III. PRE -DEVELOPMENT CONDITIONS 3.1 Major Basin Description.................................................................. 2 3.2 Pre -development Drainage Patterns ................................................ 2 IV. POST -DEVELOPMENT CONDITIONS 4.1 Post -development Conditions.......................................................... 3 4.2 Design Criteria and References....................................................... 3 4.3 Hydrologic Criteria.......................................................................... 3 4.4 Hydraulic Criteria............................................................................ 3 4.5 Detention.......................................................................................... 4 V. WATER QUALITY 5.1 Water Quality Measures and Criteria .............................................. 4 VI. EROSION CONTROL PLAN 6.1 Erosion Control Plan and Criteria .................................................... 5 6.2 Rainfall Erosion Control Plan .......................................................... 5 VII. CONCLUSIONS 7.1 Compliance with Standards............................................................. 5 REFERENCES.......................................................................................... 6 APPENDICES Appendix A — Historic Drainage Exhibit and Calculations Appendix B — Developed Drainage Calculations Appendix C — Street Capacity Calculations Appendix D — Inlet Calculations Appendix E — Stone Line Calculations Appendix F — Swale Calculations Appendix G — Detention Pond 303, 304, 305 Calculations Appendix H — SWMM Input Data, SWMM Modeling Output Appendix I — Water Quality Calculations Appendix J — Riprap Calculations BACK MAP POCKET Developed Drainage Exhibit VICINITY MAP /I% NORTHERN ENGINEERING NESERVICES, INC. June 29, 2005 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: Lemay Avenue Estates Fort Collins, Colorado Project Number: 110-004 Dear Staff: Northern Engineering Services, Inc. is pleased to submit this Final Drainage Report for Lemay Avenue Estates for your review. In general, this report serves to document the historical drainage patterns for the site and the proposed drainage design for Lemay Avenue Estates. We understand that review by the City of Fort Collins is to assure general compliance with standardized criteria contained in the Storm Drainage Design Criteria and Construction Standards. This report was prepared in compliance with technical criteria set forth in the City of Fort Collins Storm Drainage Design Criteria and Construction Standards manual. I If you should have any questions or comments as you review this report, please feel free to contact us at your convenience. Sincerely, N THERN GINEERING SERVICES, INC. Aaron Cvar, P.E. Senior Engineer 420 SOUTH HOWES, SUITE 202 / FORT COLLINS, COLORADO 80521 / 970.221.4158 / FAX 970.221.4159 Final Drainage Report for Lemay Avenue Estates Fort Collins, Colorado June 29, 2005 Prepared For: Everitt Company 3030 South College Avenue Fort Collins, Colorado 80525 Phone: (970) 226-1500 Prepared By: NORTHERN ENGINEERING SERVICES, INC. 420 S. Howes, Suite 202 Fort Collins, Colorado 80521 Phone: (970) 221-4158 Fax: (970) 221-4159 Project Number: 110-004