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 Austin
 Drainage Criteria Manual
 Section 4. INLETS
 Appendix 4.4.0. INLET SYSTEM LAYOUT

  § 4.4.3. Inlet Flow Calculation Table

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  • A suggested procedure for inlet flow design is provided below. A table of 18 columns can be used to record the value for each step in the procedure.

    Column 1. Inlet number. All inlets are classified with a designated number.

    Column 2: Drainage area number. List the identification number of all subareas draining to the inlet identified in Column 1.

    Column 3. The corresponding discharge from the drainage areas in Column 2.

    Column 4: The carry-over flow (Q pass ) in this column is the rate of flow (cfs) which bypassed the inlet immediately upstream of the inlet under consideration.

    Column 5. The total run-off, Qa, is the run-off from Column 3 plus the carry-over from preceding drainage areas.

    Column 6. The slope, S, expressed in percentage, is obtained from established grade lines as shown on the plan-profile sheets, or from specified data.

    Column 7. Gutter depression.

    Column 8. The water depth, y o , in the gutter is expressed in feet. "y o " can be determined from Equation 3-1 or Figure 3-1 (in Appendix D of this manual) for the straight crown streets and determined from Equations 3-3, 3-4 or 3-5 for the parabolic crown streets.

    Column 9. The value of the ponded width is the product of the water depth (in Column 7) and the reciprocal of the cross slope (z) in the Equation 3-2. The ponding width must be kept within the maximum permissible ponded limit of the streets.

    Column 10. The reduction factor for each inlet as specified in Section 4.3.0.

    Column 11. Q a /L a is read from Figure 4-10 in Appendix D of this manual by the gutter depression and gutter flow depth.

    Column 12. L a is calculated from Qa divided by the value in Column 11. L a represents the length of an inlet for 100 percent interception.

    Column 13. Length of the inlet L.

    Column 14. The ratio of L/L a .

    Column 15. The ratio of gutter depression (in feet) to water depth in the gutter (in feet).

    Column 16. The ratio of Q/Q a . The value is read from Figure 4-11 in Appendix D of this manual.

    Column 17. Q is the flow intercepted by the inlet of length L.

    Column 18. The carry-over flow (Q pass ) is the result of Q a -Q.