40 W. & L. E. GURLEY, TROY, NEW YORK 



Two ordinary boats may be quickly equipped at a small expense 



.i- .1 catamaran i l''ii:. 1". t'rmn which meters may he operated 

 with great facilit\. in other than flood conditions. Precise 

 results have been obtained in smooth water from a rig of 



tin- kind. 



All measuring sections that are to be maintained continu- 

 ously should have a fairly smooth bed, a uniform velocity of 

 current not less than 0.5 foot per second at any stage, unil'm-mly 

 li-trihuied throughout the section, with no strong eddies, cross 

 currents, or boils, a permanent control assuring a constant rela- 

 tion between gage height and discharge, and should not be 

 subject to marked fluctuations during the measurements. In 

 changing conditions, the flow past the control is the essential 

 factor, because the records of gage height and the rating table 

 pertain to the section at the control, and not necessarily to the 

 section in which the discharge measurements are made. A per- 

 manent reef or ledge extending across the stream (Fig. 1(> 

 short distance below the edge, will control the relation between 

 gage height and discharge, even though the bed of the measur- 

 ing section itself may change. Where no natural control exists, 

 an artificial control (Fig. 17) may be constructed. In general, 

 it has been found more economical in the long run to make 

 stream measurements where the conditions are permanent, even 

 though the cost may be greater than if the measurements were 

 made at a more easily accessible point, but with changing 

 conditions. 



