

DISTRIBUTION OF VELOCITY IN OPEN CHANNEL 339 



In a very shallow stream the vertical velocity curves approximate to 

 straight lines, and in this case the means of surface and bottom velocities 

 give a close approximation to the mean velocity. 



The main results of a large number of river gaugings by members 

 of the U.S. Geological Survey are given below. 1 



Here the symbol S means sandy ; G gravelly ; R rocky ; B boulders. 



The ratio of the velocity at mid depth to the mean velocity in any 

 vertical appears to vary very little, its usual value ranging from TO'2 to 

 r06, increasing with the depth of the stream. A value of 1*04 may be 

 relied upon as giving the mean velocity within 3 per cent, for all normal 

 sections and velocities of flow. 



ART. 96. DISTRIBUTION OP VELOCITY OVER A VERTICAL THROUGH THE 

 CENTRE OF THE STREAM. 



In spite of very many experiments which have been carried out to 

 determine the distribution of velocity, and of many attempts to formularise 

 the results of such investigations, so many and so varied are the factors 



1 U. S. Geol. Survey, Water Supply and Irrigation Papers, No. 95, pp. 150168. 



2 2 



