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 San Antonio
 Unified Development Code
 Appendix H. STORM WATER DESIGN CRITERIA MANUAL
 Chapter 9. OPEN CHANNELS
 Appendix 9.3. Design Guidelines
 Appendix 9.3.3. Constructed Channels

§ 9.3.3.1. Earthen  

Latest version.

  • The design of earthen channels shall comply with the following general requirements:

    A.

    Freeboard consistent with Table 9.3.14 will be applied to the twenty-five (25) year design.

    B.

    The side slope shall not be steeper than three (3) horizontal to one (1) vertical.

    C.

    A fifteen (15) foot access road on one side of the extreme limits of the channels is required when channels do not parallel and adjoin an alley or roadway. Where utilities are installed in the access road of the channel, the access road will be widen to seventeen (17) feet. "Extreme Limits" of the channel shall mean the side slope intercept with the natural ground or proposed finished ground elevation. Where designed channel bottoms exceed one hundred (100) feet in width, the fifteen-foot access road shall be provided on both sides of the channel. The access road will slope toward the channel with a maximum cross slope of one (1) inch per foot. Additionally, the top of utility manholes within the access road to match the finish ground surface.

    D.

    Earthen interceptor drains are for proper conveyance of upstream storm water sheet flow only. See Section 9.3.10.

    E.

    Earthen channels shall be vegetated. See Section 16.2.1.

    F.

    Channels with longitudinal slopes less than 0.5 percent or bottom widths greater than thirty (30) feet, concrete pilot channels shall be provided. The minimum bottom width of the pilot channel shall be six (6) feet. The minimum [earthen] slope draining toward the pilot channel shall be one (1) percent.

    G.

    Ensure that the channel will contain the hydraulic jump (sequent depth) throughout the extent of the supercritical profile. An exception to this criteria is where concrete lined lateral channels discharge down the side slopes of channels. These channels may be designed for normal depth plus freeboard provided velocity controls are established at the main channel flow line.

    H.

    Ensure that the energy grade of the channel will not result in upstream flooding at existing or proposed lateral facility connections.

    Example: Improved channel through the proposed development with a channel flare to accept upstream storm water should be checked with a backwater model to ensure that the hydraulic grade line and energy grade line match the pre-project conditions on the adjoining/upstream property.