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HomeMy WebLinkAboutHOUSKA AUTOMOTIVE EXPANSION - BDR - BDR150010 - REPORTS - DRAINAGE REPORT (3)Final Drainage Report For Houska Automotive Repair Fort Collins, Colorado Prepared for: D and N Houska Family, Family , LLLLLLLLCCCC c/o Dennis Houska 899 Riverside Drive Fort Collins, Colorado Prepared by: 908 Laporte Avenue Fort Collins, CO 80521 (970) 219-2834 March 30, 2016 ENGINEER’S CERTIFICATION I hereby state that this Drainage Report for the Houska Automotive Repair 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 FOR REVIEW ONLY TABLE OF CONTENTS I. INTRODUCTION ................................ ................................ ................................ ......... 1111 II. GENERAL LOCATION AND DESCRIPTION ................................ ........................... 1111 A. Property Location .................................................................................................... 1 B. Description of Property .......................................................................................... 2 C. Developed Conditions ............................................................................................ 2 III. DRAINAGE BASINS AND SUB-SUB -BASINS ................................ ................................ ... 3333 A. Major Basin Description .............................................................................................. 3 IV. DRAINAGE DESIGN CRITERIA ................................ ................................ ................. 3333 A. Four Step Process .......................................................................................................... 3 B. Development Criteria Reference and Constraints ............................................... 4 C. Hydrological and Hydraulic Criteria......................................................................... 5 V. DRAINAGE FACILITY DESIGN ................................ ................................ .................. 5555 A. General Concept ........................................................................................................... 5 B. Specific Details – Detention ........................................................................................ 5 C. Specific Details – Inlets and Storm Sewer ............................................................... 5 D. Specific Details – Stormwater Quality ..................................................................... 6 VI. SEDIMENT/EROSION CONTROL ................................ ................................ ............. 8888 VII. CONCLUSIONS ................................ ................................ ................................ ............ 8888 A. Compliance with standards ....................................................................................... 8 B. Drainage Concept ......................................................................................................... 8 VIII. REFEEEERRRREEEENNNNCCCCEEEESSSS REF ................................ ................................ ................................ ................ 9999 IX. APENDICES ................................ ................................ ................................ .................. 9999 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 Houska Automotive Repair project (the "project"). II.GENERAL LOCATION AND DESCRIPTION A. Property Location The project is located on the south side of Riverside Avenue, just southeast of the existing Houska Automotive site at 899 Riverside Avenue, and is intended to function as an extension of the existing Houska Automotive use. The site is an infill site completely surrounded by existing development. SITE Vicinity Map, NTS 2 B. Description of Property 1. The project site is an undeveloped parcel located between the existing Houska Automotive site and the private drive aisle into the Albertson’s shopping center along the south side of Riverside Avenue. 2. The project site is currently undeveloped; and is 2.28 acres in size. 3. The site is currently covered with weeds, native and volunteer vegetation; with an existing vegetative cover of approximately 60%. 4. There is no significant off-site runoff entering the site, and the site drains overland to the south curb and gutter of Riverside Avenue. 5. Existing surface soils, according to the National Resources Conservation Service, consist of Satanta Loam. The soil type is classified as hydrologic soil group B. 6. Existing soils underlying the proposed work are classified as clayey sand (SC), as identified by a soils investigation prepared by Terracon. 7. There are no irrigation ditches or stormwater conveyance systems on the property. 8. Portions of the project site are located within the City regulatory Old Town 100-year floodplain. The property is located outside the City regulatory Old Town 100-year floodway, however floodway is located inside the Riverside right-of-way adjacent to the property, as shown on the City’s online floodplain mapping. C. Developed Conditions 1. The proposed project consists of 3 buildings to support additional automotive repair uses, such as tire maintenance and general automotive repair. None of these buildings are located within the FEMA or City of Fort Collins Old Town Masterplan 100-year floodplain or floodway. 2. The project includes the relocation of the existing Houska access to provide a single access for both the existing and proposed uses, which necessitates the relocation of two existing inlets on Riverside. The project also includes private drive aisles, parking, and associated hardscape and landscaping. 3. None of the proposed buildings are located within the City regulatory Old Town 100-year floodplain or floodway. 3 4. The improvements proposed within the floodplain include a driveway, sidewalks, drainage improvements and miscellaneous site improvements. 5. The project is currently envisioned to be built in two phases. Phase one includes building one, all the public infrastructure and a temporary parking area. Phase two includes buildings two and three. The drainage design for phase one encompasses all phases of the project. 6. The developed site will drain from south to north via overland flow and swales to a proposed regional water quality pond located at the northwest corner of the site. III.DRAINAGE BASINS AND SUB-SUB -BASINS A. Major Basin Description 1. The project site lies within the Old Town drainage basin. 2. The project site currently drains overland from south to north, exiting the site along the western and northern lot lines. Runoff is received by the existing storm drainage system in Riverside Avenue and the Locust Street Outfall. IV. DRAINAGE DESIGN CRITERIA A. 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. Two bioretention ponds are proposed for the project site. These will collect much of the runoff from the developed areas. Infiltration will be encouraged and directly connected impervious areas will be minimized. This design, in combination with the highly permeable underlying soils (clayey sands) results in infiltration opportunities that do not currently exist on site. b. The percentage of proposed impervious cover is 74%. This impervious cover rate is less than allowed, and less than typical for intensive commercial development. 4 c. The vegetated areas will be heavily landscaped, in contrast to the sparse existing vegetation currently existing, allowing for decreased effective runoff coefficients. 2. Implement BMP’s That Provide a Water Capture Volume (WQCV) with Slow Release. a. The steps described above will provide attenuation for peak rates of runoff. b. Additionally, runoff attenuation and water quality treatment is provided by a regional extended detention basin to be located on the development site. This basin receives a large majority of runoff from the site prior to exiting the site. 3. Stabilize Drainageways. a. There are no 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 extended detention for a site that currently has none. 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. The combination of intensive vegetative establishment and water quality treatment through Low Impact Development (LID) techniques will allow for a reduction in particulates and adhered pollutants as compared the existing condition. B. Development Criteria Reference and Constraints 1. As previously discussed, historic drainage patterns are maintained with the proposed project. 2. As an infill project, existing topography along the boundary is maintained. 5 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. 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 south to north. Storm water runoff from the site is directed towards a proposed regional water quality pond located on the northwest corner of the site. This pond connects to the Locust Street Outfall, which runs south-to-north immediately west of the site. 2. Existing drainage patterns are maintained by the project. Runoff from the site in both conditions is collected by adjacent storm sewer systems. 3. Water quality treatment is provided with extended detention (through a regional water quality pond located on site) and Low Impact Development techniques as discussed below. B. Specific Details –––– DDDDeeeetttteeeennnnttttiiiioooonnnn 1. The project is located near at the bottom of the Old Town basin, adjacent to the Locust Street Outfall. This regional outfall consists of a 108-inch pipe directly connected to the Poudre River. Because of the location of the site, detention on site would be counter-productive since it would only serve to delay the site developed peak runoff to more closely coincide with the peak runoff from the overall drainage basin. Stormwater is proposed to runoff un-detained, allowing the runoff peak to flow into and through the outfall pipe before the larger peak from the overall basin arrives. 2. City stormwater staff, as part of the overall cooperative effort on the regional water quality pond, has modified the hydrologic modeling in the Old Town Masterplan and verified that detention is not required, nor advised, for the development. Detention is not included in the project. CCCC. . Specific Details –––– Inlets and Storm Sewer 1. Two existing storm drain inlets are located under the proposed driveway and must be relocated. It is expected that these inlets are adequately 6 sized, so identical inlets are being proposed for areas just outside of the proposed driveway. Both inlets are relocated in such a way as to ensure they continue to drain to the same receiving drainage system. a. The 5’ Type R curb inlet on the eastern side of the proposed driveway is moved approximately 17’ towards the east along Riverside. To accomplish this, the existing pipe to the existing inlet is extended to a new manhole behind the curb/gutter. The new single curb inlet is connected to the new manhole. b. The 15’ Type R curb inlet on the western side of the driveway is moved approximately 25’ towards the west along Riverside Avenue. This inlet drains to a new manhole placed on the existing receiving storm pipe from the existing inlet. The existing and proposed inlets drain to the storm vault along the Locust Street Outfall. 2. Four storm drain pipes are proposed as part of the regional water quality pond. a. Two 24-inch storm drain pipes (storm pipes 6 and 7) are proposed along the north boundary as part of the regional water quality pond. Storm pipe 7 terminates at an area drain at a point near the eastern boundary, and will serve to convey off-site discharges to the proposed regional pond. The size and general locations of these pipes are as per direction from City stormwater staff. b. A 24-inch storm drain pipe (storm pipe 5), storm manhole and a 30- inch storm drain pipe (storm drain 4) are proposed to connect the outfall structure for the regional water quality pond to the existing vault located on the Locust Street Outfall. DDDD. . Specific Details –––– Stormwater Quality 1. The City of Fort Collins, in cooperation with the developer, intends to construct a regional water quality pond within the development site. This pond will provide extended detention for a large regional drainage area, and will also provide treatment for the project site. The regional water quality pond has a storage volume of approximately 0.66 acre-feet at elevation 4961.0’. a. The City will acquire easements for the regional water quality pond and conveyance elements as needed for the regional project. b. Unfortunately, an area for Low Impact Development (LID) treatment needed for the development project will be lost to accommodate the regional project. In particular, the regional conveyance is located within areas needed for LID treatment for 7 buildings 1 and 2. Because of this, the site’s LID requirement of 75% treatment is reduced by 0.64 acres, which is the amount of LID treatment originally proposed by the developer within the lost area. The LID requirement for the development is reduced to 0.62 acres of treated drainage area (which is 1.68 acres x 75% - 0.64 acres). c. The City’s regional water quality pond will also provide standard water quality treatment for the development site through extended detention. d. The City will pay for the design, construction and other costs associated with the regional water quality pond. These costs will be offset by benefits to the development project as subsequently negotiated. e. An emergency spillway path is provided for the un-detained 100- year flow through the water quality pond. This path is towards Riverside Avenue, where the proposed elevations at the back of the sidewalk are 4961.42. This area acts as a spillway with a level crest length of 80 feet and a depth of 0.20 feet. The shallow depth combined with the concrete sidewalk, curb/gutter and paving results in a stable overflow path for emergency flows. 2. Low Impact Development (LID) water quality treatment is required for 75% of the proposed impervious area, minus 0.64 acres as previously discussed. The modified LID water quality treatment area is 0.62 acres. Two LID techniques are used to accomplish this, as follows: a. Rain Garden Bioretention Pond 1 is located in the southwestern portion of the site. This pond is located in an area that was previously constructed as a bioswale for the existing development in the Houska South development. This existing bioswale will be redesigned and reconstructed as a rain garden and bioretention pond. The new pond will handle 1.00 acres of Houska South (identified as drainage basin 5 in the drainage report for that project and drainage basin Q1B in this report) and 0.41 acres (identified as basin Q1A in this report) of new development. The total area treated is 1.41 acres. b. Rain Garden Bioretention Pond 2 is located in the northwestern portion of the site. This pond receives runoff from the central drive aisle and treats 0.29 acres. c. The total LID treated drainage area is 0.70 acres, which is higher than the required 0.62 acres as discussed above. The net LID treatment percentage for the site is 79.7%, once the credit for the lost LID treatment opportunity is accounted for. 8 3. The sizing calculations and an LID summary are included in the appendix. 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”, dated 3/30/2016, 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 Old Town Basin master plan. 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. 9 VIII. RRRREEEEFFFFEEEERRRREEEENNNNCCCCEEEESSSS 1. City of Fort Collins Storm Drainage and Design Criteria and Construction Standards. 2. Old Town Drainage Master Plan; Anderson Consulting, July 15, 2003. 3. Urban Storm Drainage Criteria Manual Volume 1-3; Urban Drainage and Flood Control District, Denver, Colorado, April 2008. 4. Geotechnical Engineering Report, Houska Large Truck Facility; Terracon (project number 20155048), dated 11/11/2015. 5. Final Drainage and Erosion Control Report, Houska Automotive Auto Parts Warehouse; North Star Design, April 9, 2012. IX. APENDICES Appendix I - Hydrologic Calculations  Peak Discharge Calculations Appendix II - Hydraulic and Water Quality Calculations  LID Stormwater Management Summary Worksheet  Bioretention Sizing Worksheets  Outfall Pipe Sizing Worksheet  Emergency Spillway Sizing Report Appendix III - Mapping and Plans  Annotated Flood Insurance Rate Map  Drainage Exhibit (24”x36”) 10 Appendix I – Hydrology