online_culvert:   Hydraulic design of highway culverts by FHWA method



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The program ONLINE_CULVERT calculates the diameter for the hydraulic design of a culvert using the FHWA Method for three types of culverts:

  • Square edge with headwall,

  • Groove end with headwall, and

  • Groove end projecting.

To determine the culvert diameter D, the calculator requires the following information:

  • Design discharge Q (positive number)

  • Inlet invert elevation z1 (positive number)

  • Manning's n (allowable range: 0.013-0.030)

  • Natural stream bed slope So (allowable range: 0.0001-0.1)

  • Tailwater depth above outlet invert y2 (positive number)

  • Culvert length L (positive number)

  • Shoulder elevation Es (must be greater than inlet invert elevation z1)

  • Freeboard Fb (zero or positive number)

  • Entrance loss coefficient Ke (a choice between 1.0, 0.5, 0.12, and 0.03) (Pipe entrance in Table 5-3)

  • Exit loss coefficient KE (a choice between 1.0, 0.92, 0.72, 0.42, and 0.16) (Expansion in Table 5-3)

Source:  Roberson, Hydraulic Engineering.

The output consists of:  (1) culvert diameter D, (2) critical depth yc, (3) normal depth yn, (4) number of iterations, (5) type of flow (supercritical/subcritical), (6) presence of hydraulic jump/hydraulic drop, and (7) type of control (inlet/outlet).

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