Open Channel Flow  Gradually Varied Flow     (continued)                 

 

Conclusions based on the Specific Energy Plot for Open Channel Flow of a rectangular
channel are detailed in the following table.

                   

 

 

 

Any flow condition

 

 

Flow rate at a certain depth is completely specified by
 any two of the variables  y, q, V, and E except the

combination  q and E, which yields, in general, two

alternate depths

 

 

For any value of specific energy, E

 

 

For any value of   E  there exists a critical depth for

which the flow is a maximum.  yc = 2/3 Emin

 

 

For any value of  q

 

 

For any value of   q  there exists a critical depth for which the specific energy is a minimum.   yc = (q2/g)1/3

 

 

When flow occurs at the critical depth

 

 

When flow occurs at the critical depth the velocity head

is one-half the depth.      Vc2/2g  =  ½ yc

 

 

 

 

For any flow condition other than critical

 

 

For any flow condition, other than critical, there exists an alternate depth at which the same flowrate is carried by the same specific energy.  The alternate depth may be found by extending a vertical line to the alternate limb on the specific energy diagram.

 

 

 

 

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