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HomeMy WebLinkAboutDrainage Reports - 10/29/2021SCOTT, COX & ASSOCIATES, INC. consulting engineers • surveyors 1530 55th Street • Boulder, Colorado 80303 • (303) 444-3051 • Fax: (303) 444-3387 October 29, 2021 Mr. Jim Bray Bray Architecture, Inc. 1300 Yellow Pine, Unit C Boulder, Colorado 80304 Reference: Drainage Letter – The Post Chicken & Beer 1002 South College Avenue – Fort Collins, Colorado Scott, Cox & Associates Project No. 21101 Dear Mr. Bray: This letter is submitted as the final drainage letter of the existing and proposed conditions for the property located at 1002 South College Avenue, in Fort Collins, Colorado. INTRODUCTION The site is located in the northwest quarter of Section 13, Township 7 North, Range 69 West of the 6th Principal Meridian in the City of Fort Collins, Larimer County, State of Colorado. The site is bounded by E. Elizabeth Street and commercial properties to the north, an asphalt alley and residential properties to the east, commercial properties to the south, South College Avenue and Colorado State University to the west. This report is being prepared to accompany the Building Permit application for the project. The purpose of this drainage letter is to address specific drainage issues related to the proposed site changes. EXISTING ON-SITE DRAINAGE The 0.32 acre site is currently developed with a commercial/restaurant building located at the north side of the site. The site generally slopes from the southwest corner to the northeast corner at an average slope of 2%. Under the existing conditions, the site will be divided into three (3) sub-basins, Basin E1- E3. City of Fort Collins Approved Plans Approved by: Date: Dan Mogen 10/29/2021 Mr. Jim Bray Bray Architecture, Inc. October 29, 2021 Page 2 of 4 Drainage from Basin E1 consists of the west portion of the parking lot and the southwest portion of the building. Runoff from this basin flows west via sheet flow to Design Point No. 1. From there, the runoff flows north via gutter flow along South College Avenue, then east along E. Elizabeth Street, and continues east towards the existing storm sewer system located at the intersection of E. Elizabeth and Remington Streets. Drainage from Basin E2 consists of the northern portion of the building. Runoff from this basin flows north and east via sheet flow to Design Point No. 2. From there, the runoff flows east via gutter flow along E. Elizabeth Street towards the existing storm sewer system located at the intersection of E. Elizabeth and Remington Streets. Drainage from Basin E3 consists of the east portion of the parking lot. Runoff from this basin flows east via sheet and shallow concentrated flow to Design Point No. 3 and discharges into the adjacent alley ROW. The alley then flows north into the E. Elizabeth Street ROW, and then east towards the existing storm sewer system located at the intersection of E. Elizabeth and Remington Streets. EXISTING OFF-SITE DRAINAGE There is one (1) offsite basin that effects the site. Drainage from Basin OS1 consists of the northeast portion of the adjacent commercial property to the south. Runoff from within this basin flows north via sheet and shallow concentrated flow, through Basin E3 to Design Point No. 3 and discharges into the adjacent alley ROW. PROPOSED ON-SITE DRAINAGE The proposed improvements include the renovation of the existing commercial/restaurant building, new mechanical yard, new dining patio and restriping of the existing parking lot. The parking lot has generally remained as is with the exception of the existing CMU screen wall located on the east side of the lot, adjacent to the public alley. Portions of this wall have been removed in order to provide better vehicular circulation into the alley. Mr. Jim Bray Bray Architecture, Inc. October 29, 2021 Page 3 of 4 The Proposed Drainage Plan shows the proposed site plan, on-site grading and overland flow directions. Under the proposed conditions, the site will be divided into four (4) sub- basins, Basin A1-A4. Drainage from Basin A1 consists of the west portion of the parking lot and the southwest portion of the building. Runoff from this basin flows west via sheet flow to Design Point No. 1. From there, the runoff flows north via gutter flow along South College Avenue, then east along E. Elizabeth Street, and continues east towards the existing storm sewer system located at the intersection of E. Elizabeth and Remington Streets. Drainage from Basin A2 consists of the northern portion of the building. Runoff from this basin flows north and east via sheet flow to Design Point No. 2. From there, the runoff flows east via gutter flow along E. Elizabeth Street towards the existing storm sewer system located at the intersection of E. Elizabeth and Remington Streets. Existing Sub-Basin E3 is now split into two (2) developed sub-basins, Basin A3 and A4. Drainage from Basin A3 consists of the proposed mechanical yard. Runoff from this basin flows north and east via sheet flow to Design Point No. 3 and discharges into the adjacent alley ROW. The alley then flows north into the E. Elizabeth Street ROW, and then east towards the existing storm sewer system located at the intersection of E. Elizabeth and Remington Streets. Drainage from Basin A4 consists of the east portion of the parking lot. Runoff from this basin flows east via sheet and shallow concentrated flow, through the new opening in the screen wall to Design Point No. 4, and discharges into the adjacent alley ROW. The alley then flows north into the E. Elizabeth Street ROW, and then east towards the existing storm sewer system located at the intersection of E. Elizabeth and Remington Streets. Drainage from Basin OS1 will drain through Basin A4 to Design Point No. 4 and discharge into the adjacent alley ROW. The modifications made to the existing screen wall will not affect conveyance of the offsite flow. The historical drainage patterns for this offsite basin will remain unchanged. The Design Point No. 4 is located only twenty (20’) south of Design Point No. 3, where the historic drainage from Basin E3 historically drained. Mr. Jim Bray Bray Architecture, Inc. October 29, 2021 Page 4 of 4 The imperviousness of the site has remained unchanged from existing conditions. The runoff rate from the minor and major storm has also remained unchanged. CONCLUSIONS We feel that the proposed changes for storm water discharge from this site is minor and will not affect the overall drainage patterns adjacent to the site and within the ROW. The discharge from the site will not adversely affect the adjacent properties. The proposed improvements will maintain the historic drainage patterns that were established during the original construction. Therefore, it is our conclusion that the peak runoff for the initial and major storm events from the tributary basin can be conveyed directly to the major drainage system without adverse impact to upstream, surrounding, or downstream properties and facilities. Should you have any questions or comments concerning this letter, kindly give us a call. Sincerely, SCOTT, COX & ASSOCIATES, INC. Donald P. Ash, P.E. Chief Civil Engineer Attachments: Existing Drainage Plan Proposed Drainage Plan