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HomeMy WebLinkAboutWARD ALTERNATIVE ENERGY - PDP - PDP160002 - SUBMITTAL DOCUMENTS - ROUND 1 - DRAINAGE REPORTFinal Drainage Report For Ward Alternative Energy Fort Collins, Colorado Prepared for: Ward Alternative Energy, LLC c/o Paul Nelson 5660 E. 58th Avenue Commerce City, CO 80022 Prepared by: 908 Laporte Avenue Fort Collins, CO 80521 (970) 219-2834 January 13, 2016 ENGINEER’S CERTIFICATION I hereby state that this Drainage Report for the Ward Alternative Energy project 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 TABLE OF CONTENTS I. INTRODUCTION ................................................................................................. 1 II. GENERAL LOCATION AND DESCRIPTION ........................................................ 1 A. Property Location ............................................................................................................... 1 B. Description of Property .................................................................................................... 2 C. Developed Conditions ...................................................................................................... 2 III. DRAINAGE BASINS AND SUBBBB-SU -BASINS ............................................................... 3 A. Major Basin Description ........................................................................................................ 3 IV. DRAINAGE DESIGN CRITERIA ............................................................................ 3 A. Detention Criteria ............................................................................................................... 3 B. Water Quality – the Four Step Process ............................................................................ 3 B. Development Criteria Reference and Constraints ....................................................... 4 C. Hydrological and Hydraulic Criteria .................................................................................. 4 V. DRAINAGE FACILITY DESIGN ............................................................................ 5 A. General Concept ...................................................................................................................... 5 B. Specific Details – Detention ................................................................................................. 5 C. Specific Details – Inlets and Storm Sewer ........................................................................ 6 VI. SEDIMENT/EROSION CONTROL ........................................................................ 6 VII. CONCLUSIONS ................................................................................................... 6 A. Compliance with standards ................................................................................................. 6 B. Drainage Concept ................................................................................................................... 6 VIII. REFERENCES ....................................................................................................... 7 IX. APENDICES ......................................................................................................... 7 1 I. INTRODUCTION This report presents the pertinent data, methods, assumptions, and references used in analyzing and preparing the final drainage and water quality design for the Ward Alternative Energy project (the "project"). II.GENERAL LOCATION AND DESCRIPTION A. Property Location The project is located within property owned by Larimer County, located at 614 East Vine Drive in Fort Collins, Colorado. The project is located on a 1.07 acre portion of the property known as the Larimer County Shops Minor Subdivision, which is located on the northeast corner of the intersection of Vine Drive and Redwood Street. Vicinity Map, NTS 2 B. Description Descrip tion of Property 1. The project site is within the “Larimer County Shops Minor Subdivision”, on land currently occupied by Larimer County facilities and fleet operations. The project site is intended to be subdivided into a separate lot. 2. The project site is currently developed, with a large metal building and asphalt paving. 3. There is no significant off-site runoff entering the site, and the site drains overland to the southwest. Stormwater is collected in a low area immediately northeast of the intersection of Vine and Redwood, discharging to an existing storm drain pipe. This pipe is connected to an existing inlet along the eastern curb/gutter of Redwood Street. 4. Existing surface soils are classified as Nunn Clay Loam. Underlying soils consist of sand and gravel, as identified by a soils investigation prepared by CTL/Thompson. These underlying soils are highly permeable. 5. There is no City or FEMA 100-year floodplain or floodway located on the project site. However, portions of the project site are located within the Poudre River shaded FEMA Zone X (500-year) flood zone, as shown on FIRM panel 08069C0977G. An annotated copy of the Firmette for this area is included in the Appendix. C. Developed Conditions 1. The proposed project is a natural gas fueling station, consisting of 5 fuel islands with canopy covers, and a masonry enclosure to house equipment. This project is a joint effort between Larimer County and Ward Alternative Energy, with Ward in the developer role. As a result, there is also an “off-site” improvement consisting of a paved drive aisle to the rear portion of the Larimer County shops. 2. The project includes private driveways off Vine Drive and Redwood Street and paved drive aisles for customers; and the drive aisle for the Larimer County shop. As a result, the detention drainage area is somewhat larger than the actual proposed lot. 3. The project will be constructed in one phase. 4. The developed site will drain from northeast to southwest in the same direction as the existing condition. A drainage/extended detention pond is proposed for an area west of the site, within an unused remnant right- of-way (ROW). This ROW was originally envisioned for Redwood Street, 3 however the planned alignment of Redwood was changed and this area is currently not in use for any public purpose. It is expected that a use agreement will be entered into with the City of Fort Collins to allow the detention pond to be located within the ROW. III.DRAINAGE BASINS AND SUB-SUB -BASINS A. Major Basin Description 1. The project site lies within the Dry Creek drainage basin. The Dry Creek Masterplan calls for developing property to manage runoff to a flowrate of 0.20 CFS/acre. IV. DRAINAGE DESIGN CRITERIA A. Detention Criteria 1. As previously mentioned, the project site is within the Dry Creek Basin. Detention is required to mitigate the increased runoff anticipated due to development of the site. The release rate for the site is 0.20 CFS/acre. BBBB. . Water Quality –––– the Four Step Process The stormwater management strategy for the project is the “Four Step Process”, with the goal of minimizing adverse impacts of urbanization on receiving waters. The following is a description of the steps employed to achieve this goal. 1. Employ Runoff Reduction Practices a. Pervious interlocking concrete paves will comprise over 25% of the new paving proposed. These pavers are located in two distinct areas, which will treat contributing drainage areas. The underlying soils are sands and gravels; and are very porous. This will allow pervious pavers with no under drain system, resulting in infiltration and runoff reduction. b. The detention pond area is expansive and located over underlying sands and gravels. There is a naturalized drainage swale in that area that will be left undisturbed. It is expected that the combination of a broad shallow storage area and the pervious underlying soils will encourage a significant amount of infiltration and runoff reduction. 2. Implement BMP’s That Provide a Water Capture Volume (WQCV) with Slow Release. 4 a. The steps described above will provide attenuation for peak rates of runoff. b. Additionally, runoff attenuation and water quality treatment is provided by an Extended Detention Basin. This basin receives a large majority of runoff from the site prior to exiting the site. 3. Stabilize Drainageways. a. There are no existing significant drainageways or conveyances within the project site, and the site drains directly to existing storm sewer systems. However, off-site benefit is achieved through the use of stormwater detention and extended detention for a site that currently has neither. By providing these improvements, discharges are attenuated and treated for water quality. b. Stormwater impact fees and month stormwater utility fees will be paid by this development. This additional revenue will contribute to the overall City programs to stabilize drainageways throughout the city. 4. Implement Site Specific and Other Source Control BMP’s. a. A Grass Buffer strip is proposed to provide additional LID treatment for runoff from the site. This combination of water quality treatment through Low Impact Development (LID) techniques will allow for a reduction in particulates and adhered pollutants as compared the existing condition. The LID and contributing drainage areas are shown on the enclosed Drainage Exhibit. A summary of LID treatment parameters is also included in the Appendix. B. Development Criteria Reference and Constraints 1. There are no known development-related drainage studies for the site. 2. The proposed project is intended to comply with current City of Fort Collins development drainage criteria. C. Hydrological and Hydraulic CCCCrrrriiiitttteeeerrrriiiiaaaa 1. Hydrologic and hydraulic criteria is as per the City of Fort Collins Storm Drainage and Design Criteria and Construction Standards. 5 2. Analyses are performed using City of Fort Collins spreadsheets and the methodologies presented in Urban Storm Drainage Criteria Manual Volumes 1, 2 and 3; Urban Drainage and Flood Control District, Denver, Colorado. V. DRAINAGE FACILITY DESIGN A. General Concept 1. The general direction of proposed storm water flow is from northeast to southwest, which matches the existing drainage pattern. 2. Storm water runoff from the site is directed via overland flow towards a detention/water quality pond located adjacent to the southwest corner of the site. 3. There is one drainage basin for the detention pond, referred to as Basin A. As previously discussed, this basin is 1.50 acres in size. 4. Additional drainage sub-basins are delineated for the various LID features internal to the site. These include Q1, Q2 and Q3. Q1 and Q2 discharge to pervious paving. Q3 discharges to a grass buffer strip. 5. The Water Quality Capture Volume is treated with extended detention located within the detention pond. 6. These drainage features are shown on the Drainage Exhibit in the Appendix. B. Specific Details –––– DDDDeeeetttteeeennnnttttiiiioooonnnn 1. As previously mentioned the drainage area for detention is 1.5 acres. The allowable release rate is 0.20 CFS/acre, therefore the release for the detention pond is 0.30 CFS. Due to topographic constraints, 0.14 acres is not able to drain to the proposed stormwater management pond. 2. The detention pond is located off-site in remnant ROW. The topography of this area is very conducive to a detention pond. The area is low and drains through an existing pipe to an existing inlet on the eastern curb/gutter of Redwood Street. The proposed pond outlet structure is simply added to the end of the existing storm pipe; and a limited amount of grading is needed to create the required storage volume. 3. The required detention volume was calculated using the City’s FAA rational formula based detention pond design worksheet. 6 4. An emergency spillway path is provided for the un-detained 100-year flow from the site. This path is located in the drive aisle onto Vine Drive. The section consists of an inverted crown with curb/gutter and concrete paving. The location of the spillway is shown on the enclosed Drainage Exhibit. A weir analysis indicates that the capacity of the weir is 36.8 CFS, which far exceeds the calculated un-detained 100-year peak runoff under developed conditions of 13 CFS. CCCC. . Specific Details –––– Inlets and Storm Sewer 1. There are no inlets or storm sewers proposed with the project. VI. SEDIMENT/EROSION CONTROL Temporary erosion control measures will be implemented with this project, as detailed under a separate report entitled “Erosion and Sediment Control Report”, prepared by Apex Engineering. Please see that document for more information on the temporary best management practices proposed to control sediment and erosion during construction. VII. CCCCOOOONNNNCCCCLLLLUUUUSSSSIIIIOOOONNNNSSSS A. Compliance with standards 1. All drainage design conforms to the criteria and requirements of City of Fort Collins Storm Drainage Design Criteria and Construction Standards. 2. Proposed drainage improvements conform to the concepts and recommendations of the Dry Creek Basin master plan. B. Drainage Concept 1. The proposed drainage plan concept for the project will effectively manage both peak rates of discharge and water quality impacts, conforms to City of Fort Collins standards. 7 VIII. RRRREEEEFFFFEEEERRRREEEENNNNCCCCEEEESSSS 1. Fort Collins Stormwater Criteria Manual, City of Fort Collins, Colorado, as adopted by Ordinance No. 174, 2001, and referenced in Section 26-500 © of the City of Fort Collins Municipal Code. 2. Urban Storm Drainage Criteria Manual Volume 1-3; Urban Drainage and Flood Control District, Denver, Colorado, April 2008. 3. Geotechnical investigation, Proposed Storage Building and Fueling Facility”; CTL/Thompson (project number FC07179-125), dated 12/17/2015. IX. APENDICES Appendix I - Hydrologic Calculations  Peak Discharge Calculations Appendix II - Hydraulic and Detention Calculations  Detention Pond FAA Worksheet  Detention/WQ Pond Sizing Worksheet  Emergency Spillway Sizing Report Appendix III - Mapping and Plans  Firm Panel 08069C0977G  Drainage Exhibit (24”x36”) 8 Appendix 1 – Hydrologic Calculations 9 10 11 12 Appendix II – Hydraulics 13 14 15 16 Appendix III – Mapping and Plans 17