The URL can be used to link to this page

Home My WebLink AboutLEMAY AVENUE ESTATES - PDP - 37-04 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORT�re'q 4 ti Ruipm • •— Y � ,: lira ^ •. •: � 4 t ' r"" ��1 _ y .:: �.:i+nvt•.Nus nacre ati.:^CC d rh . • y'r A CL y r \ �T'� 4 rYY, •i '' + ' ...., r: , r arr 9`�1 � �IS�j�yiy�. i Rd m; Y '1 PROJECT h` SITE 14 i ,aIjRe t fi 1 Momid r, �TANTON CREEK d00—YR FLOODPLAIN LIMITS Turm In Dr b m ikkRrrN'iL .. AlOne Cis' C)iT ( tl VICINITY MAP ° 1500 1500 3000 ssco eet NORTHERN ENGINEERING ( IN FEET) SERVICES, INC. 1 inch = 1500 ft. 420 South Howes Street, Suite 202, Fort Collins, Colorado 80521 Phone: (970)221-4158,Fax (970)221-4159 APPENDIX A Vicinity Map Preliminary Drainage Report Lemay Avenue Estates February 2, 2005 REFERENCES Northern Engineering Services, Inc. 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, Latimer 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 9 Preliminary Drainage Report Lemay Avenue Estates February 2, 2005 Northern Engineering Services, Inc. made to minimize any negative impacts on the downstream receiving waters. A variance is requested to allow Basin OS-1, located at the northwest comer of the site, to release undetained into the eastern roadside ditch of Lemay Avenue. Basin OS-1 consists of the adjacent half -street of Lemay Avenue running along the northwest comer of the site and is 0.97 acres in size. Drainage from this basin will travel to the north in the roadside ditch. Drainage from this basin was not incorporated into the site drainage design, due to grade restrictions. Page 8 IPreliminary Drainage Report Northern Engineering Services, Inc. Lemay Avenue Estates ' February 2, 2005 V. WATER QUALITY 5.1 Water Quality Measures and Criteria 1:. The primary water quality method will be built into Detention Ponds 302, 303, and 304. Water quality capture volume (WQCV) will be provided in these ponds in order to ' remove sediment and other pollutants from developed runoff. Based on criteria for a 40- F hour dry extended detention basin outlined in the Urban Storm Drainage Criteria Manual '' Volume 3 — Best Management Practices by the Urban Drainage and Flood Control District (September 1999), the required water quality capture volume for Ponds 302, 303 and 304 is respectively, 0.54 ac-ft, 0.023 ac-ft, and 0.021 ac-ft. A steel orifice plate with 'c vertical perforations will be built into the outlet structures of these ponds to control the water quality capture volume. 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. Wattles will be placed in swales at an interval of no less than 200 feet (preferably at 2' vertical intervals). 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. VII. 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 Page 7 Preliminary Drainage Report Lemay Avenue Estates February 2, 2005 Northern Engineering Services,. Inc: carryover flow from Basin D1 will travel to the east to Inlet Al and Pond 302. The carryover flow from Basin D2 will travel to Inlet B I and Pond 301. Basin El and E2 Basins E1 and E2 are located in the eastern portion of the site. These basins consist of a mixture of residential lots and detention ponds. Composite C-values have been calculated for the basins based on the recommended C-values (and correction factors) based on impervious areas of each. An assumed house and driveway layout has been used to calculate impervious areas for the residential lots. This includes impervious area for driveways, sidewalks, and roofs (See Appendix C). Drainage from Basin E1 travels overland to discharge directly into detention Pond 301. Drainage from Basin E2 travels overland to discharge directly into detention Pond 302. Basin F1 Basin F1 is located in the northeastern portion of the site. This basin consists of the back half of two residential lots. Composite C-values have been calculated for the basin based on the recommended C-values (and correction factors) based on impervious areas. An assumed house and driveway layout has been used to calculate impervious areas for the residential lots. This includes impervious area for driveways, sidewalks, and roofs (See Appendix C). Drainage from Basin 171 travels overland to discharge directly into Stanton Creek. The difference in the 100-year developed runoff value for Basin F1 was compared to the 2-year historic runoff rate to establish the available release for Pond 302. Basin GI. G2, and G3 Basins Gl, G2, and G3 are located at the southern and eastern edge of the site. Basins G1 and G2 consist of the back half of residential lots. Composite C-values have been calculated for the basin based on the recommended C-values (and correction factors) based on impervious areas. An assumed house and driveway layout has been used to calculate impervious areas for the residential lots. This includes impervious area for driveways, sidewalks, and roofs (See Appendix Q. Basin G3 consists of the southern portion of Lemay Avenue as well as the back half of some of the residential lots. A Type R inlet will be placed on grade to intercept flow from Basin G3 and direct it into Pond 304. Drainage from Basin G1 will be directed by a Swale into Pond 303. Drainage from Basin G2 travel overland south and be released undetained into Stanton Creek. The difference in the 100-year developed runoff value for Basin G2 was compared to the 2- year historic runoff rate to establish the available release for Pond 302. Basin OS-1 Basin OS-1 is located on the western edge of the site. Basin OS-1 consists of the northern portion of Lemay Avenue (eastern half of roadway). Drainage from this basin was not incorporated into the site drainage design, due to grade restrictions. A variance will be requested to allow the drainage from this portion of the site to discharge off -site undetained. Page 6 ' Preliminary Drainage Report Lemay Avenue Estates ' February 2, 2005 Nor -them Engineering Services, Inc. 4.6 Drainage Patterns Basin AI Basins Al is located in the northeastern portion of the site. These basins consist of a mixture of residential lots and proposed roadway. Composite C-values have been calculated for the basins based on the recommended C-values (and correction factors) based on impervious areas of each. An assumed house and driveway layout has been used to calculate impervious areas for the residential lots. This includes impervious area for driveways, sidewalks, and roofs (See Appendix Q. Drainage from Basin Al travels overland to the eastern portion of Rawah Drive. Rawah Drive slopes to the east to a sump condition in the cul-de-sac where Inlet Al will intercept flows and discharge into Pond 302. Basin B1, B2, B3 and B4 Basins B 1 through B4 are located in the central portion of the site. These basins consist of a mixture of residential lots and proposed roadway. Composite C-values have been calculated for the basins based on the recommended C-values (and correction factors) based on impervious areas of each. An assumed house and driveway layout has been used to calculate impervious areas for the residential lots. This includes impervious area for driveways, sidewalks, and roofs (See Appendix C). Drainage from Basins B1, B2 and B3 travels overland to Showline Road, Diamond Tail Drive, Honholtz Drive, and Laramie River Drive. Drainage from Basins B4 travels overland to the southern portion of Rawah Drive and Laramie River Drive. Laramie River Drive and Honholtz Drive slopes to the east to a sump condition directly east of Detention Pond 301. Inlets B1 and B2 will intercept flow and discharge into Pond 301 via Storm Line B. Basin CI Basin C 1 is located in the western -central portion of the site. The basin consists of a mixture of residential lots and proposed roadway. Composite C-values have been calculated for the basins based on the recommended C-values (and correction factors) based on impervious areas of each. An assumed house and driveway layout has been used to calculate impervious areas for the residential lots. This includes impervious area for driveways, sidewalks, and roofs (See Appendix Q. Drainage from Basin C1 travels overland to Robert's Run. Robert's Run slopes to the east to a sump condition in the cul- de-sac where Inlet Cl will intercept flow and discharge into Pond 301. Basin DI and D2 Basins D 1 and D2 are located in the northwestern portion of the site. These basins consist of a mixture of residential lots and proposed roadway. Composite C-values have been calculated for the basins based on the recommended C-values (and correction factors) based on impervious areas of each. An assumed house and driveway layout has been used to calculate impervious areas for the residential lots. This includes impervious area for driveways, sidewalks, and roofs (See Appendix C). Drainage from Basins D1 and D2 travels overland to Showline Road and Diamond Tail Drive. Showline Road slopes to the north and then travels east toward Pond 301. On -grade combination Inlets D 1 and D2 will intercept approximately 75% of flow and discharge into Pond 301. The Page 5 Preliminary Drainage Report Northern Engineering Services, Inc. Lemay Avenue Estates ' February 2, 2005 design. • The computer program "FlowMaster v6.1 [614o]" by Haestad Methods will be used to analyze swales and major storm street capacities. • The Excel spreadsheet "UD-Inlet v1.06a" by Urban Drainage and Flood Control District will be used to analyze inlet sizes and minor storm 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, and 304 will also be utilized to provide water quality capture volume in their lower stage. 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 calculated by taking the allowable 2-year historic release rate of 11.3 cfs (37.8 ac. x 0.299 cfs/ac) and subtracting off the difference between proposed Basins F1 and G2 100-year runoff value (8.91 cfs) and their 2-year historic runoff value (2.1 cfs). This results in a final allowable release rate from Pond 302 of 4.5 cfs (11.3 cfs — (8.91 cfs — 2.1 cfs)). Basins F1 and G2 drainage was subtracted off because these basins will discharge directly into Stanton Creek undetained. Pond 303 will discharge into Stanton Creek. The release rate from Pond 303 of 0.56 cfs is based on the allowable 2-year historic release rate of 0.299 cfs per acre. Pond 304 will discharge into the existing roadside ditch along the east side of Lemay Avenue. The release rate from Pond 304 of 0.33 cfs is also based on the allowable 2-year historic release rate of 0.299 cfs per acre. Table 2 summarizes the detention pond results. TABLE 2 Detention Storage Summa Maximum Maximum Detention plus 100-year Water Quality Discharge Capture Volume Pond (cfs) (ac-ft) 301 4.0 6.60 (detention only) 302 3.0 2.94 303 0.56 0.21 304 0.33 0.20 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 and 304. An outlet box with vertical perforations will control the water quality volume. Page 4 Preliminary Drainage Report Northern Engineering Services, Inc. Lemay Avenue Estates ' February 2, 2005 I 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. Four 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 and 304 were sized using the FAA Method (See Appendix Q. There will be two outfalls into Stanton Creek, one from Pond 302 and one from Pond 303. 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 0.25 was used for lawns and landscaped areas, assuming a clayey soil value. 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 and 304. 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 3-1 a updated by the City of Fort Collins in 1999. Rainfall data for SWMM has been taken from Figure 3-1 c, also updated by the City of Fort Collins in 1999. 4.4 Hydraulic Criteria The followingcomputer programs will be used in the proposed design P p gr p p of the storm systems for the site at final design: The computer program "StormCAD v4.1.1 [4.2014a]" by Haestad Methods will be used to design and analyze the storm sewer lines and outlet pipes in final Page 3 1 Preliminary Drainage Report Lemay Avenue Estates February 2, 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 Drainage Outfalls Maximum 2-year Release Area Peak Flow Rate Location (Acres) (cfs) (cfs/ac) Existing undeveloped field 43.33 13.0 0.299 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 I00-year floodplain boundary for Stanton Creek has been shown on the drainage exhibit for the project, and will not be altered by this t 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 currently runs empty 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. Page 2 Preliminary Drainage Report Northern Engineering Services, Inc. Lemay Avenue Estates February 2, 2005 Preliminary Drainage Report for Lemay Avenue Estates Fort Collins, Colorado February 2, 2005 1►Y Y:T�Zi11li�I�Ti7�i 1.1 Obi ective This report summarizes the results of a comprehensive analysis of both pre- and post - development hydrologic and hydraulic conditions for the Graece Property 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 Surveying 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 comer 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. II. 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 southwestern quarter of Section 18, Township 6 North, Range 68 West of the 6a' 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 western -central portion of the site. The site soils are primarily sandy lean clay, 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 1 Table of Contents VICINITY MAP Page I. INTRODUCTION 1.1 Objective.......................................................................................... 1 1.2 Mapping and Surveying................................................................... 1 1.3 Site Reconnaissance......................................................................... 1 II. SITE LOCATION AND DESCRIPTION f2.1 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 =kz 4.4 Hydraulic Criteria .............. 3 4.5 Detention.......................................................................................... 4 4.6 Drainage Patterns............................................................................. 5 V. WATER QUALITY 5.1 Water Quality Measures and Criteria .............................................. 7 VI. EROSION CONTROL PLAN 6.1 Erosion Control Plan and Criteria .................................................... 7 6.2 Rainfall Erosion Control Plan .......................................................... 7 ' VII. CONCLUSIONS P 7.1 Compliance with Standards............................................................. 7 REFERENCES.......................................................................................... 9 APPENDICES APPENDIX A - Vicinity Map APPENDIX B - Historic Drainage Analysis APPENDIX C - Rational Method Hydrology and FAA Calculations APPENDIX D - SWMM Modeling & Water Quality Calculations I NORTHERN ENGINEERING NESERVICE% INC. February 2, 2005 City of Fort Collins Stormwater Utility 700 Wood Street Fort Collins, Colorado 80521 RE: Lemay Avenue Estates Fort Collins, Colorado Project Number: 04-088.00 Dear Staff: Northern Engineering Services, Inc. is pleased to re -submit this Preliminary 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. If you should have any questions or comments as you review this report, please feel free to contact us at your convenience. Sincerely, NORTHERN ENGINEERING SERVICES, INC. L L- Aaron Cvar, P.E. A04i Senior Engineer 7vi-45—, ........ •'.i 420 SOUTH HOWES, SUITE 202 / FORT COLLINS, COLORADO 80521 1 970.221.4158 / FAX 970.221.4159 Preliminary Drainage Report for Lemay Avenue Estates Fort Collins, Colorado February 2, 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: GRA (04-088.00)