High chord elevation at upstream side of bridge

The average elevation of the high chord (or highest part of the superstructure that blocks the flow) on the upstream side of the bridge. The elevation of the high chord is used by the program to determine the vertical blockage of flow caused by the bridge superstructure. This in turn is used to determine the thickness of the pressure flow separation zone, t. Please refer to FHWA Manual HEC-18, Fifth Edition, Section 6.10 for a discussion of the procedure for estimating pressure flow.

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