April 14, 2017

Normal Flow vs Gradually-Varied Flow

In normal flow the down-slope component of weight balances bed friction. As a result, the
water depth h and velocity V are constant and the total-head line (or energy grade line) is
parallel to both the water surf
ace and the channel bed; i.e. the friction slope Sf is the same as
the geometric slope S
0.






As a result of disturbances due to hydraulic structures (weir, sluice, etc.) or changes to
channel width, slope or roughness the downslope component of weight may not locally
balance bed friction. As a result, the friction slope Sf and bed slope S0 will be different and
the water depth h and velocity V will change along the channel.
The gradually-varied-flow equation gives an expression for dh/dx and allows one to predict
the variation of water depth along the channel.



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