FLOOD00178

• County: Statewide
• Title: Application of the HEC-2 Bridge Routines - Training Document Number 6
• Date: 6/1/1974
• Prepared For: US
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

If the expansion coefficient (Ke) is taken as 1.0, the equation can
be rewritten into the form of the orifice equation by adding the con-
tinuity equation (Q = VA).
Q = A1I2gH/K (6)
where:

K = Kb + 1

The loss coefficient used in the program's orifice equation can

be related to the loss coefficient C from another commonly used orifice

flow equation, Q = CA~. The conversion (XKOR = 1/C2) can be used

in utilizing tabulated values of C. However, care must be taken to in-

sure the definition of h used in the various formulations is applicable.

The Bureau of Public Roads (reference j) shows experimental values

for C for fully submerged conditions to vary from 0.7 to 0.9. A value

of 0.8 is recommended as being applicable for the average two to four
lane concrete girder bridge. The definition of h is consistent with
that used in HEC-2. In the absence of calibration data, a value of

1.56 for XKOR (C = 0.8) would be applicable to most bridges and short

culverts. For longer culverts, the coefficients given in Exhibit 2 of

HEC-2 Users Manual can be used to compute XKOR as follows:

X~R = k + kf + 1
e
where:
ke = entrance loss coefficient
kf = friction loss coefficient

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