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Unformatted text preview: ortant, and a recommended correction [19] is
Low heads, H 50 mm: Cd, V notch 0.9
(Re We)1/6 0.44 (10.61) where Re
g1/2H3/2/ and We
gH2/ , with being the coefficient of surface tension. Liquids other than water may be used with this formula, as long as Re
300/tan ( /2)3/4 and We 300.
A number of other thinplate weir designs — trapezoidal, parabolic, circular arc, and
Ushaped — are discussed in Ref. 21, which also contains considerable data on broadcrested weirs. Backwater Curves A weir is a flow barrier which not only alters the local flow over the weir but also modifies the flowdepth distribution far upstream. Any strong barrier in an openchannel flow creates a backwater curve, which can be computed by the gradually varied
flow theory of Sec. 10.6. If Q is known, the weir formula, Eq. (10.55), determines H and
hence the water depth just upstream of the weir, y H Y, where Y is the weir height.
We then compute y(x) upstream of the weir from Eq. (10.51), following in this case an
M1 curve (Fig. 10.14c). Such a barrier, wher...
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 Spring '08
 Sakar

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