HY8:Box Inlet Drop Structure
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The input variables required for this calculation is the following:
- HD — Desired drop height. Must be between 2 and 12 ft or between 0.6 and 3.7 m.
- New Slope — The slope that will exist on the channel once the drop structures are in place (The new slope must be subcritical).
- Box Length — Length of box inlet. (USER'S CHOICE)
- W2 — Width of box inlet. Must fit criteria (.25 < HD/W2 < 1)
- W3 — Width of the Downstream End of Stilling Basin. This must be equal to or larger than the culvert width.
- Flare of Stilling Basin (1 Lateral: Z long) — This value must be greater than or equal to 2, which is to say 1 lateral: 2 Long)
- Length from Toe of Dike to Box Inlet — If a dike is used, the distance from the toe of the dike to the box inlet must be entered. If no dike is used, enter a value of 100 ft or 30.48 m for this distance.
The following figure shows a plan and side view of a box inlet drop structure.
Variables from the figure
- W1 — Width of the upstream end of the basin
- W2 — Width of box inlet crest
- W3 — Width of the downstream end of the basin
- W4 — Distance from the toe of dike to the box inlet
- L1 — Length of box inlet
- L2 — Minimum length for the straight section
- L3 — Minimum length for final section (potentially flared)
- H0 — Drop from crest to stilling basin floor
- h2 — Vertical distance of the tailwater below the crest
- h3 — Height of the end sill
- y0 — Required head on the weir crest to pass the design flow
- y3 — Tailwater depth above the floor of the stilling basin
- h4 — Sill height