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HomeMy WebLinkAboutSummary ReportBleyl & Associates Project Engineering & Management March 17, 2008 Josh Norton, EIT Planning and Development Services City of College Station P 0 Box 9960 College Station, TX 77842 RE : Executive Summary Report ReMax of Br)ian/College Station Office Building Dear Josh, 1 722 Broadmoor Suite 210 Bryan, TX 77802 As required by the City of College Station, Bleyl and Associates has prepared a Stormwater Management Technical Design Summary Report for submission and review for the referenced project. This report includes the Executive Summary Report, a completed Technical Design Summary, maps showing pre and post development drainage areas, and other reference material needed for.your review. CONTACT INFORMATION 1. ENGINEER: Sam J. Vernon Bleyl & Associates 1722 Broadmoor Drive Suite 210 Bryan , Texas 77802 2. OWNER: Tim Ware 526 University Drive East, Ste 101 B College Station, Texas 3. SUBMITTAL DATE: February 25, 2008 GENERAL PROJECT INFORMATION The owner wishes to build an office building for ReMax of B/CS and associated improvements including a parking lot, water and sewer facilities , and landscaping. The property is 1.371 acres and the proposed improvements will affect all but a 20' wide strip along the west boundary. There are no additional phases planned. We have previously submitted permit applications for both clearing and grading , and site plans. The Case File Number is #08-00500014 for the site plan . Bryan (979)-268-1125 (979)-260-3849 Austin (512)-328-7878 (512)-328-7884 Fax Conroe (936)-441-7833 (936)-760-3833 Fax PROJECT LOCATION The proposed 1.37 acre project site is located on University Drive approximately 2100 feet east of the intersection of the northbound frontage road of State Highway 6 Bypass and University Drive (FM 60). The property is within the Hudson Creek Watershed. The west line of the tract is approximately 250 feet east of Hudson Creek. Because of its proximity to a primary channel , no detention is required. The entire property falls within the city limits of College Station. I have also included a letter to Alan Gibbs determining that the floodway does not impinge upon our property. HYDROLOGIC CHARACTERISTICS Land cover on the property is mostly a dense Buffalo or prairie grass. The eastern side of the site is approximately six feet higher than the western half. Existing runoff sheet flows from east to west, concentrating into several evident drainage paths on the western edges of the site and across the tract of land currently owned by M.J. Talk. On the higher ground are scrub trees such as mesquite. As the tract slopes toward the creek, the grass becomes denser with stands of several large pecans, elms, and hackberry trees along the western line. The subject property is bounded on two sides by Veteran's Park. The build out for the park is being done in phases, and currently there are no improvements near the ReMax site. Approximately 0.24 acres of this park land flows onto and across the site. Runoff coming down the FM 60 ditch also cuts across the very northeast corner where the fill slopes have been constructed out almost to ReMax's north line. STORMWATER MANAGEMENT Owing to the proximity to the site and Hudson Creek, no detention of runoff is required, so our stormwater plan is to essentially capture and convey runoff across the new site and releasing it in two areas along the northerern boundary. Offsite drainage will be handled in the following manner. Referring to the pre development drainage map, area Pre-1 is 0.25 acres in area. By the post developed plans, approximately ~ of that will enter the parking lot and travel west until discharge. The remaining are will flow into our site and around the new building exiting along the south line into a drainage easement within the park. A rather large amount of water from the east has been intercepted from the TxDOT right of way and A&M property bounding Veteran's Park and diverted into the park via a trapezoidal channel. This channel is on the order of 6 feet deep with a bottom dimension ranging from 8 to 10 feet in width. With this in mind, the culvert under the proposed driveway now is only needed to convey water from a narrow strip approximately 1100 feet in length. Our very conservative submission to TxDOT is for a 24" RCP . To date, we have not been notified if that is acceptable in their judgment. Stormwater will exit the parking lot through a curb cut located in the north west corner of the parking lot and a sump location along the proposed access driveway. The discharge rate of the runoff flowing across the parking lot is estimated as follows: 50% Event 20% Event 10% Event 4% Event 2% Event 1% Event 2.66 cfs 3.60 cfs 4.26 cfs 5.04 cfs 5.92 cfs 6.34 cfs During the 1 % event, assuming a relatively even split between each of these openings, this translates to an exit velocity of less than 3 feet per second. Grading for construction will consist of importing, placing and compacting close to five feet of material to bring the building site up and out of the floodplain . There was an existing drainage easement along the western half of the property. The owner released a portion to Mr. Ware for full use. This document is included for your review. There is a 20 foot wide drainage easement that will remain along the western boundary. A retaining wall will be built on the easement line to keep this strip natural and intact. COORDINATION In October of 2007, Brett McCully submitted a letter to Alan Gibbs concerning the floodway determination in this area. In that letter it was pointed out where the map graphics did not match the HEC 2 printout. In a subsequent phone conversation with Alan, Brett said that he concurred with these findings and agreed that the entire site was out of the floodway. We have submitted a driveway permit application to TxDOT. As of this date, we have not gotten a response from them. REFERENCE This Summary Report including all maps, calculations, and attachments, one 24-page design summary dated February 25, 2008, one set of construction drawings (3 sheets) dated February 25, 2008 comprise the drainage report for this project. Please contact me with any questions, or if you require any additional information to complete your technical review of this project.