82 



BACKWATER CURVES IN UNIFORM CHANNELS 



From the logarithmic plots, shown on Fig. 702, the empirical equations 

 representing the straight lines are found to be 



— = 7340/-18 



and 



IAS6'A^R"^ 



= 42,300,000y-3« 



Since in this example n did not vary with the depth, it is obvious that the 

 multiplier lAS^/n'^ could have been omitted in determining the exponent b. 

 It would have to be included in computing the value of a, however. 



200 



100 



^|fs 



10 



10 12 14 16 18 21 25 

 Values of y 



2X10' 



IXIO' 



5x10" 

 4X10" 



3X10" 

 2X10" — 



IX 10" 



10 12 14 16 18 21 25 



Values of y 



Fig. 702. Logarithmic Plot for the Determination of the Coefificients and Exponents 

 in Empirical Equations (704) and (705). 



By the other method 



log 20.35 -log 1.11 __. 

 C = — : —z : ~z — = J.lo 



and 



b = 



log 25 - log 10 



log 214.5 - log 9.68 

 log 25 - log 10 



= 3.38 



