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Home My WebLink AboutPreliminary Drainage Report 111924 200 Casey Drive, Maumelle, AR 72113 | Work: 501.851.3366 November 19, 2024 Mr. Dylan Warner City of Little Rock 723 W. Markham Street Little Rock, AR 72201 RE: The Reserve at Brodie Creek Preliminary Storm Drainage Calculations Little Rock, Arkansas Mr. Warner, Please see the attached preliminary storm drainage basin and detention calculations for the above referenced project located off West 36th Street, at your earliest convenience. The numbers are based on site field surveys and mapping reviews. If there are any questions or concerns regarding this project, please do not hesitate to contact me at 501-851-3366 or Dustin@Holloway-eng.com. The preliminary storm drainage analysis for this project was created using Hydraflow Hydrographs Extension and Hydraflow Express for Civil 3D. Per the City of Little Rock Storm Drainage Ordinance, the Rational Method of calculating runoff was used since the onsite drainage area for this project is less than 200 acres. The existing site is approximately 64.70 acres and will be developed as a single-family subdivision. Existing offsite drainage conveys to the site via channelized flow coming from 272.2 acres on the north side of W 36th Street as well as from 63.266 along the south side of W 36th Street but north of the project site. The stormwater on the north side of W 36th Street is separated into 3 s eparated waterways and flows through 3 separate pipe systems before draining onto the project site. The offsite contributing areas along the south side of W 36th Street are separated into two areas which flow naturally onto the project site and one area which is channelized by an existing pipe system before draining to the project site. We are proposing to construct a new open channel to ditch to collect the upstream offsite stormwater and convey it south the existing Brodie Creek waterway. Onsite runoff will be captured by new stormwater pipe systems which will also capture and convey stormwater to the Brodie Creek waterway. Thank you for your assistance. Sincerely, Dustin Welch, EI, AC Channel Report Hydraflow Express Extension for Autodesk® Civil 3D® by Autodesk, Inc. Tuesday, Nov 19 2024 <Name> Trapezoidal Bottom Width (ft) = 20.00 Side Slopes (z:1) = 1.00, 1.00 Total Depth (ft) = 4.00 Invert Elev (ft) = 324.00 Slope (%) = 1.50 N-Value = 0.027 Calculations Compute by: Known Q Known Q (cfs) = 1043.00 Highlighted Depth (ft) = 3.42 Q (cfs) = 1,043 Area (sqft) = 80.10 Velocity (ft/s) = 13.02 Wetted Perim (ft) = 29.67 Crit Depth, Yc (ft) = 4.00 Top Width (ft) = 26.84 EGL (ft) = 6.06 0 5 10 15 20 25 30 35 40 Elev (ft) Depth (ft)Section 323.00 -1.00 324.00 0.00 325.00 1.00 326.00 2.00 327.00 3.00 328.00 4.00 329.00 5.00 Reach (ft)