232 BOTTOM VELOCITY AT WHICH SCOUR COMMENCES. 



50, and that of its lower CO square feet, the mean value of 

 its wetted perimeter being 36 feet, we have 



8.025 \/0.9167 



_ _, 000768 - 



602 50 2 -t 110 + 



025A /I ""kJ67~ 



V - 0.0001222 + 0.0007549 



= 305 cubic feet. 

 The mean of these values is 



352.5 + 305.5 



Q - - = 329 cubic feet. 



/i 



Sen. The following is Chezy's formula, with three dif- 

 ferent coefficients, varying from 69 "for small streams 

 under 2000 cubic feet per minute," to 96 "for large rivers 

 such as the Clyde or the Tay." 



v = 69 (r sin 6)$. For small streams. 

 v = 93 (r sin 0)i Eytelwein's coefficient. 

 v = 96 (r sin 0)*. For large streams. 



124. Bottom Telocity at which Scour Com- 

 mences. A river channel is said to have a fixed regimen, 

 when it changes little in draft or form in a series of years. 

 In some rivers, the deepest part of the channel changes its 

 position perpetually, and is seldom found in the same place 

 two successive years. The sinuousness of the river also 

 changes by the erosion of the banks, so that in time the 

 position of the river is completely altered. In other rivers, 

 the change from year to year is very small, but probably the 

 regimen is never perfectly fixed except where the rivers flow 

 over a rocky bed. If a river had a constant discharge, it 



