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



MEASUREMENTS IN ARTIFICIAL CHANNELS 



Current meter measurements of the flow of water in artificial 

 channels must be made with special care, as the laws of flow 

 for open channels are not always applicable to artificial ones, 

 because the water level may be subjected to disturbing influ- 

 ences such as undercurrents caused by intakes and outlets at 

 rapid velocities. 



Current meters have been employed in measuring the flow 

 in large conduits. In such cases apparatus designed to hold 

 the meter at a definite point in the cross-section has been used. 

 The description of such apparatus will be found in the Transac- 

 tions of the American Society of Civil Engineers, 1910, Vol. 66. 



Current meters have also been used successfully for 

 measuring the flow of sanitary sewers. Details of this work 

 are given on page 142. 



ACCURACY AND RELIABILITY OF THE 

 CURRENT METER 



When considering the accuracy of results obtained by the 

 current meter, account should be taken of the use to be made 

 of the data. It must be remembered that both the total flow of 

 the stream and its distribution over the drainage area are con- 

 stantly changing, and that the conditions over the drainage area 

 are constantly changing, and that the conditions existing at any 

 given time will probably never occur again. The flow which 

 may be expected in any stream, therefore, can be determined 

 only by studying a series of records extending over a long 

 period; for this reason the degree of refinement with which the 

 measurements are made should be appropriate to the use to 

 which they are to be put. 



As with most instruments, the accuracy and reliability of 

 the current meter depend largely on the care taken in the 

 measurement and the propriety of the method used. 



