Loading...
HomeMy WebLinkAboutHOUSKA AUTOMOTIVE EXPANSION - BDR - BDR150010 - REPORTS - DRAINAGE REPORTFinal 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 February 10, 2016 ENGINEER’S CERTIFICATION I hereby state that this Drainage and Erosion Control 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 ................................ ................................ ............. 7777 VII. CONCLUSIONS ................................ ................................ ................................ ............ 7777 A. Compliance with standards ....................................................................................... 7 B. Drainage Concept ......................................................................................................... 7 VIII. REFEEEERRRREEEENNNNCCCCEEEESSSS REF ................................ ................................ ................................ ................ 8888 IX. APENDICES ................................ ................................ ................................ .................. 8888 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 it 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. 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 storm drain system located at the northwest corner of the site. A small portion of the flows on the east and south edges of the site will run off the site un-detained. These flows are significantly less than the existing flows leaving 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. Vegetated bioswales are proposed along the northern, eastern and western boundaries of the project site. These will convey much of the runoff to the proposed regional stormwater management pond and minimize directly connected impervious areas. The soft surface swale located in the stormwater management pond is serpentine in shape and will be heavily vegetated. This design, in combination with the highly permeable underlying soils (clayey sands) results in infiltration opportunities that do not currently exist on site. 4 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. 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 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 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. 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. 5 2. As an infill project, existing topography along the boundary are maintained. 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 north south 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 which is directly connected to the Poudre River. Because of the location of the site, detention on site would be counter-productive. 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. 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 sized, so identical inlets are being proposed for areas just outside of the 6 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. DDDD. . Specific Details –––– Stormwater Quality 1. As previously mentioned, the City of Fort Collins, in cooperation with the developer, intends to construct a regional water quality pond on site. This pond will provide extended detention for a large regional drainage area, and will include treatment for the project site. The regional water quality pond has a storage volume of approximately 0.71 acre-feet at elevation 4961.0’, although those figures are expected to change as the pond goes through final design. a. 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 4961.04. This area acts as a spillway with a level crest length of 40 feet and a depth of 0.25 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. The project includes 1.682 acres of impervious area, therefore LID treatment is required for 1.262 acres of impervious area. Three LID techniques are used to accomplish this, as follows: a. Water Quality Basin Q1 is 0.408 acres in size and is located along the western edge of the site. This area includes building 3 and the interim asphalt parking area proposed in the same location. This area is 0.408 acres in size and is treated with a Bioswale. There is an existing bioswale in this location that was associated with the Houska South subdivision project. This bioswale is proposed to be widened by an average of 11.1 feet. The existing perforated 7 underdrain will remain. The rim of the existing area inlet will be raised to elevation 4962.0’ to provide an overflow path. b. Water Quality Basin Q2 is 0.640 acres in size and is located along the northern and eastern boundary of the site. This area is treated with a bioswale 330’ in length, with an average width of 8.4’. c. Water Quality Basin Q3 is located in the center of the site and drains to a proposed bioretention pond. The drainage area for this pond is 0.249 acres. d. The total area treated is 1.297 acres, which represents 77.1% of the proposed impervious area. 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 2/10/2016, 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. 8 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. IX. APENDICES Appendix I - Hydrologic Calculations  Peak Discharge Calculations Appendix II - Hydraulic and Detention Calculations  LID Stormwater Management Summary Worksheet  Bioretention Sizing Worksheet  Emergency Spillway Sizing Report Appendix III - Mapping and Plans  Annotated Flood Insurance Rate Map  Drainage Exhibit (24”x36”) 9 Appendix 1 – Hydrology 10 11 12 Appendix II – Hydraulics 13 14 15 16 Appendix III – Mapping and Plans 17