TUFLOW Forum

# 1D Loss Coefficients for Bridge Deck Surcharging

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Q:

Why is the loss coefficient set to 1.56 when flow is surcharging against a bridge deck in a 1D bridge channel?

A:

The loss coefficient is derived from AustRoads, Waterway Design. Refer specifically to Figure 5.18 (pg 47, 1994 edition) (attached)

The discharge coefficient, Cd, for a surcharging deck is 0.8, as shown highlighted in the attached figure

Assuming that V=Q/(bn*Z) and rearranging the equation given at the bottom of the figure, one arrives at V=Cd* (2g* dh)^(0.5). Where bn is the net waterway width.

Also given the loss formula used by the ESTRY engine dh=k*(V^2/2g), the final formula is k=1/(Cd^2).

Thus, using a Cd of 0.8 as stated in AustRoads, k=1.5625.

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