eLaws | eCases | Texas Statutes | Texas Administrative Code | Texas Courts | Counties & Cities of Texas | Code of Federal Regulations | United States Code |
 San Antonio
 Unified Development Code
 Appendix H. STORM WATER DESIGN CRITERIA MANUAL
 Chapter 10. CULVERTS
 Appendix 10.3. Design Guidelines
 Appendix 10.3.4. Energy Losses Through Culvert

  § 10.3.4.3. Full Flow at Outlet and Free Surface Flow at Inlet - Type BA  

Latest version.

  • If the frictional slope is less than the culvert slope and the outlet depth (H o ) is greater than the soffit of the culvert at the outlet then the culvert may flow full for a portion of its length.

    First determine the length of full flow using Equation 10.3.4.3.a.

    (Equation 10.3.4.3.a)

    35-H10-3-4-3a.png

    L f = length over which full flow occurs (ft.)
    S o = culvert slope (ft./ft.)
    S f = friction slope (ft./ft.)
    H o = outlet depth (ft.)
    D = Conduit barrel height (ft.)

    Should the length L f be greater than the culvert length, the culvert is flowing full for its entire length, see Type B calculations on the previous page. If the length of L f is less than the culvert length, a free surface flow begins a point along the culvert at a distance of L f from the culvert outlet. From this point up to the culvert inlet the water surface can be calculated using the standard step backwater method.

    With the water surface (H i ) or d i (shown on Figure 10.3.4.3 below) at the culvert inlet, the headwater elevation at the entrance can be calculated. See Energy Balance at Inlet section 10.3.5 on following page.

    35-H10-3-4-3.png

    Figure 10.3.4.3 - Point at Which Free Surface Flow Begins
    (Source TxDOT, Hydraulic Design Manual, 2011)