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 Okaloosa County
 Code of Ordinances
 Appendix E. LAND DEVELOPMENT CODE
 Chapter 6. DEVELOPMENT DESIGN STANDARDS

  § 6.06.102. Open channels.  

Latest version.

  • Open channels shall be designed, constructed and maintained in accordance with the following criteria:

    1.

    Design frequency: Open channels shall be designed to convey, without damage, and to confine within the channel, flow with the design frequencies identified below:

    TYPE OF CHANNEL
    		FREQUENCY
    Roadside Ditches, Median Ditches or Swales 10-year
    Outfall Ditches 25-year
    Canals 25-year

     

    2.

    Hydrologic analysis: Acceptable hydrologic methods for open channel design include USGS regression equations, the rational equation, and NRCS methodology, provided the project meets published limitations of the methodology selected.

    3.

    Hydraulic design: The Manning's Equation shall be used for the design of open channels.

    4.

    Protective treatment: The design of open channels shall consider the need for channel lining. Permissible linings for various flow velocities appear below. For purposes of channel lining, velocities shall be computed using Manning's Equation and assume the channel is flowing full.

    Maximum Shear Stress Values and Allowable Velocities for Different Soils
    Soil Type
    		Shear Stress
    (psf)
    		Allowable Velocity
    For a flow depth of about 3 ft. (ft./sec.)
    Silt or Fine Sand 0.027 1.50
    Sandy Loam 0.037 1.75
    Silt Loam 0.048 2.00
    Firm Loam 0.075 2.50
    Stiff Clay 0.260 3.75
    Hardpans 0.670 6.00

     

    ;adv=9;Reference: University of Florida (1972).

    Source: FDOT Drainage Manual.

    Maximum Velocities for Various Lining Types
    Lining Type
    		Maximum Velocity
    (fps)
    Grass with Mulch Bare Soil (see table above)
    Sod 4
    Staked Sod 5
    Lapped Sod 5.5
    Erosion Control Blanket (Biodegradable) 6.5
    Plastic Erosion Mat
    Type 1 10
    Type 2 14
    Type 3 18
    Riprap 6
    Other flexible FHWA HEC-15
    Geotextile Grid 4—8*
    Rigid 10**

     

    *Varies with grid.

    **Higher velocities acceptable with provision for energy dissipation.

    Source: FDOT Drainage Manual.

    5.

    Swales cannot be used in meeting the required stormwater storage.

    6.

    Swales shall be designed with sufficient grade to promote positive flow of stormwater to the designed downstream storage facilities. A minimum slope of 0.3 percent will be presumed to promote positive flow.

    7.

    Driveways that intersect swales designed to conform to the swale contour will show the driveway elevations on the plans.

(Ord. No. 11-01, § 2, 1-18-11)