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Home My WebLink AboutHICKORY COMMONS - PDP - PDP110005 - REPORTS - DRAINAGE REPORTPreliminary Drainage, Erosion Control and Water Quality Report For Hickory Commons Fort Collins, Colorado Prepared for: CHARLES MESERLIAN 700 NORTH COLLEGE AVENUE FORT COLLINS, CO 80524 Prepared by: AAAApex pex Engineering 908 LAPORTE AVENUE FORT COLLINS, CO 80521 970-219-2834 OCTOBER 24, 2012 Preliminary Drainage Report Hickory Commons ENGINEER’S CERTIFICATION I hereby state that this Preliminary Drainage and Erosion Control report for the Hickory Commons subdivision was prepared by me or under my direct supervision for the owners thereof and meets or exceeds the criteria in the City of Fort Collins Storm Drainage Design Criteria and Construction Standards. ------------------------------------------- Stacy J. Gowing Registered Professional Engineer State of Colorado No: 34290 Preliminary Drainage Report Hickory Commons TABLE OF CONTENTS I. INTRODUCTION ............................................................................................. 3 II. GENERAL LOCATION AND DESCRIPTION .............................................. 3 A. Property Location ...................................................................................................................... 3 B. Description of Property ............................................................................................................ 3 III. DRAINAGE BASINS AND SUB-BASINS ...................................................... 4 A. Major Basin Description ........................................................................................................... 4 B. Existing Conditions ..................................................................................................................... 4 C. Developed Conditions .............................................................................................................. 4 IV. DRAINAGE DESIGN CRITERIA .................................................................... 5 A. Development Regulations ........................................................................................................ 5 B. Development Criteria Reference and Constraints ............................................................. 5 C. Hydrological Criteria ................................................................................................................. 5 D. Hydraulic Criteria ...................................................................................................................... 5 V. DRAINAGE FACILITY DESIGN ..................................................................... 5 A. General Concept ........................................................................................................................ 5 B. Specific Details – Detention ..................................................................................................... 6 C. Specific Details – Stormwater Quality .................................................................................. 7 D. Specific Details – Swales ........................................................................................................... 7 E. Specific Details – Inlets and Storm Sewer ............................................................................. 7 F. Specific Details – Curb Cuts ..................................................................................................... 8 VI. SEDIMENT/EROSION CONTROL ................................................................ 8 A. General Concept ........................................................................................................................ 8 VII. CONCLUSIONS ............................................................................................... 8 A. Compliance with standards ...................................................................................................... 8 B. Drainage Concept ....................................................................................................................... 9 VIII. REFERENCES .................................................................................................. 10 IX. APENDICES ..................................................................................................... 11 Preliminary Drainage Report Hickory Commons I. INTRODUCTION This report presents the pertinent data, methods, assumptions, and references used in analyzing and preparing the final drainage, erosion control and water quality design for the Hickory Commons subdivision project (the "project"). II. GENERAL LOCATION AND DESCRIPTION A. Property Location 1. The project is located on the north side of Hickory Street. The legal description is: A tract of land located in the Southeast One-quarter of Section 2, Township 7 North, Range 69 West of the Sixth Principal Meridian being all of Lots 1 through 8, Block 21, of the Riverside Park Subdivision, a subdivision of record in the City of Fort Collins, except the West 5 feet thereof and together with the West Half of the vacated portion of Fourth Avenue; and all of Lots 9 through 18, Block 21, of the said Riverside Park Subdivision, together with the East Half of the vacated Alley and that part of the West Half of the vacated portion of Fourth Avenue in Block 21 of the said Riverside Park Subdivision, County of Larimer, State of Colorado. SITE Vicinity Map, NTS B. Description of Property 1. The project site is currently undeveloped. The proposed use is multi-use live/work project consisting of 26 two-story units in 7 separate buildings. The project also includes widening of Hickory Street, utilities and site improvements such as garages, parking areas, drive aisles, hardscape and landscaping. Preliminary Drainage Report Hickory Commons III. DRAINAGE BASINS AND SUB-BASINS A. Major Basin Description 1. The project site lies within the City of Fort Collins Cache La Poudre River Basin. 2. The project site is located outside the 100-year and 500-year floodplains, as shown in the following image from the City of Fort Collins website: SITE B. Existing Conditions 1. The project site is currently undeveloped. The site is currently covered with native and volunteer vegetation, and slopes gently from north to south at approximately 1%. C. Developed Conditions 1. The site will drain from north to south through a series of storm sewers and overland flow paths. The majority of the developed flows will ultimate drain through a detention/water quality pond to a proposed storm outfall pipe along Hemlock Street towards the west. A small portion of the flows on the west, east, and south edges of the site will run off the site undetained. These flows are significantly less than the existing flows leaving the site. 2. The off-site storm outfall pipe will be a public line, serving adjacent properties as well as the Hickory Commons site. Preliminary Drainage Report Hickory Commons IV. DRAINAGE DESIGN CRITERIA A. Development Regulations 1. Design criteria from the City of Fort Collins Storm Drainage and Design Criteria and Construction Standards were followed for this drainage report. B. Development Criteria Reference and Constraints 1. The proposed storm water release rate is 4.71 CFS, which is the capacity of an 18” RCP pipe at 0.2%. The outfall pipe is proposed as a 21” RCP, which has capacity for 7.11 CFS. The remaining capacity of 2.4 CFS is allocated to adjacent properties as shown on the enclosed Drainage and Erosion Control Plan. C. Hydrological Criteria 1. Peak flow rates for the 100-year storm have been calculated in accordance with the City of Fort Collins Storm Drainage and Design Criteria and Construction Standards. Please see these calculations in the Hydrology section of Appendix I. D. Hydraulic Criteria 1. The City of Fort Collins Storm Drainage and Design Criteria and Construction Standards are used to determine the adequacy of the hydraulic structures associated with the project. 2. Analyses are performed using methodologies presented in Urban Storm Drainage Criteria Manual Volumes 1 and 2; Urban Drainage and Flood Control District, Denver, Colorado, September, 1999. Please see the various computation spreadsheets in the Hydraulics section of Appendix 1. V. DRAINAGE FACILITY DESIGN A. General Concept 1. The general direction of proposed storm water flow is from north to south. 2. Storm water from the improved section along Hickory Street and the majority of the site flow though a series of storm sewers to a proposed detention pond located at the southwest corner of the site. Additional detention is provided within the drive aisle. The detention pond ultimately discharges to a proposed off-site storm outfall pipe located within the ROW for Hemlock Street. This Preliminary Drainage Report Hickory Commons pipe ultimately discharges to a natural drainageway near the entrance to the McMurry Natural Area. 3. No easements are required from Natural Areas since the entire off-site outfall pipe is located within the public ROW along Hemlock Street. B. Specific Details – Detention 1. The drainage area for the site is 2.09 acres, which includes the project site and Hickory Street located along the frontage of the site. Only 1.89 acres on the project site is able to drain to the detention pond, however 2.09 acres is the calculated area that will be treated for detention and water quality by the new detention pond. a. The release rate for the project is proposed to be 4.71 CFS, which is the capacity of an 18” RCP at 0.2% slope. It should be noted that additional capacity is provided in the 21” RCP outfall storm pipe to allow for adjacent properties to drain to this public storm drain pipe. b. The drainage basin is 80% impervious, which requires 0.069 acre-feet of extended detention volume. The water quality volume is provided at elevation 4973.23’. The calculations for the water quality volume are located in the appendix. c. The required detention volume was calculated using the City’s rational formula based detention pond design worksheet. The required detention volume is 0.196 acre-feet. The total required volume of 0.265 acre-feet is provided at elevation 4974.68’. The calculations for the detention volume are located in the appendix. d. A relatively small amount of detention volume is provided in the drive aisle. The maximum depth of the 100-year ponding in the drive aisle is 0.5’. e. There are 0.20 acres of the site on the west, south, and east borders that will not drain to the detention pond and will instead runoff the site undetained and untreated. These flows which are represented by Basin B and C and total 1.01 cfs for the 100-year storm and 0.19 cfs for the 2-year storm. This is less than the existing 100-year runoff from the site, which is 2.79 cfs, but more than the existing 2-year runoff from the site which is only 0.06 cfs. If it is critical that the proposed 2-year runoff be reduced, additional BMP’s such as a rain garden, sand filter or dry well will be incorporated into the design. 2. As previously mentioned, the detention pond drains to a proposed public off- site storm outfall pipe located within the ROW for Hemlock Street, ultimately discharging to the Cache La Poudre River. Preliminary Drainage Report Hickory Commons 3. An emergency spillway path is provided in the emergency vehicle access off Hemlock Street. The spill elevation for this structure is 4974.7’. The depth required to convey the developed un-detained 100-year discharge from the site is 0.5’. C. Specific Details – Stormwater Quality 1. Water quality will be provided in accordance with Best Management Practices as presented in the Urban Storm Drainage Criteria Manual Volume 3, Best Management Practices; Urban Drainage and Flood Control District, Denver, Colorado, September, 1999. 2. Permanent structural BMP’s will consist of extended detention within the proposed detention pond. See the above discussion of the detention pond for more details. D. Specific Details – Swales 1. There is an 8’ wide swale with 5:1 side slopes to the east of the property boundary on City of Fort Collins Parks property. This swale is designed to convey the 133% of the 100-year storm for Basin B. This 8’ wide swale and landscaping adjacent to the 10’ wide concrete trail will be maintained by the developer as per an agreement between the two parties. E. Specific Details – Inlets and Storm Sewer 1. Runoff discharges from Hickory Street are collected in a proposed Type R inlet located in a sump condition. The drainage area to this inlet is quite small, and a 5’ Type R inlet is more than adequate to collect the developed 100- year runoff discharge. 2. The majority of the discharges from the site are collected by proposed Type 13 inlets in the drive aisle. These flows are conveyed along with the flows from Hickory Street through a series of storm sewers to the detention pond. 3. The minor flows on the western side of the site will be collected in a trench drain adjacent to the sidewalk. 4. Detailed sizing calculations for storm sewer within the site will be provided with the Final Drainage Report at a later date. The storm sewers are proposed at a slope of 0.4%. The total discharge through this on-site pipe network is expected to be 9.90 CFS, which can be adequately conveyed by a 21” RCP. Therefore, the proposed storm sewer sizes will range from 15” to 21” in size. 5. An off-site storm sewer is proposed to convey discharges from the site to the Poudre River. This 21” RCP has a capacity of 7.11 CFS. As previously Preliminary Drainage Report Hickory Commons discussed, the release rate for the project site has been established as 4.71 CFS. Since the release rate for future developments contributing to this storm sewer is 0.20 CFS/acre, the excess capacity of 2.40 CFS will accommodate 12 acres of additional development from adjacent properties. The only property that does not have the ability to connect to this new storm outfall is the property immediately to the west. This property (identified as basin OS1) is 1.09 acres in size, and will generate 0.22 CFS of discharge in the developed and detained condition. A pipe is currently being shown to the western property boundary which could allow that property to connect to this property’s storm sewer system. Any additional excess capacity will be available for other properties in the area as needed. F. Specific Details – Curb Cuts 1. There are no curb cuts proposed with the project. VI. SEDIMENT/EROSION CONTROL A. General Concept 1. Temporary erosion control measures will be installed with this project. These measures will include: a. Silt fence along the property lines. b. Straw bale barriers surrounding the inlets and the discharge structure of the pond. c. Water trucks and soil terracing to address construction dust abatement. d. Vehicle tracking pad at the construction entrances. e. The detention pond will act as a sediment basin during construction. 2. Permanent sediment\erosion control measures will consist of paving, concrete hardscape, and landscaping to stabilize the disturbed areas. 3. Maintenance of all sediment\erosion control devices will remain the responsibility of the contractor until the project is completed. VII. CONCLUSIONS A. Compliance with standards 1. All drainage design conform to the criteria and requirements of City of Fort Collins Storm Drainage and Design Criteria and Construction Standards. 2. Proposed drainage improvements conform to the concepts and recommendations of the Dry Creek Basin master plan. Preliminary Drainage Report Hickory Commons 3. Proposed sediment/erosion control measures conform to the recommendations of City of Fort Collins Storm Drainage and Design Criteria and Construction Standards and generally accepted erosion control procedures. B. Drainage Concept 1. The proposed drainage plan concept for the project will be effective for the control of stormwater runoff and water quality for the proposed site and conforms to City of Fort Collins standards. Preliminary Drainage Report Hickory Commons VIII. REFERENCES • City of Fort Collins Storm Drainage and Design Criteria and Construction Standards • The Dry Creek Basin Master Plan • Urban Storm Drainage Criteria Manual Volume 1; Urban Drainage and Flood Control District, Denver, Colorado, March, 1969. • Urban Storm Drainage Criteria Manual Volume 2; Urban Drainage and Flood Control District, Denver, Colorado, March, 1969. • Urban Storm Drainage Criteria Manual Volume 3, Best Management Practices; Urban Drainage and Flood Control District, Denver, Colorado, September, 1999. Preliminary Drainage Report Hickory Commons IX. APENDICES Appendix I - Hydrologic Calculations Runoff Curve Number Time of Concentration and Peak Discharge Appendix II - Hydraulic and Detention Calculations Water Quality Calculations Detention Pond Sizing Worksheet Pond Stage-Storage Worksheet Storm Sewer Calculations Appendix III - Mapping and Plans Drainage and Erosion Control Plan (24”x36”) Preliminary Drainage Report Hickory Commons Appendix 1 – Hydrology Preliminary Drainage Report Hickory Commons Preliminary Drainage Report Hickory Commons Preliminary Drainage Report Hickory Commons Preliminary Drainage Report Hickory Commons Preliminary Drainage Report Hickory Commons Preliminary Drainage Report Hickory Commons Preliminary Drainage Report Hickory Commons Preliminary Drainage Report Hickory Commons Appendix II - Hydraulics Preliminary Drainage Report Hickory Commons Preliminary Drainage Report Hickory Commons Preliminary Drainage Report Hickory Commons Preliminary Drainage Report Hickory Commons Preliminary Drainage Report Hickory Commons Preliminary Drainage Report Hickory Commons Preliminary Drainage Report Hickory Commons Appendix III – Mapping and Plans