THE IRRIGATION AGE. 



293 



IRRIGATION WATER MEASURING DEVICES 



*By California Agents of Irrigation Investigations, Office of Experiment Stations, U. S. Department of Agriculture 



Fig. 20 A Dethridge meter in operation 



'T'HIS is the 

 * fifth of a 

 series of articles 

 prepared from a 

 bulletin issued by 

 the College o f 

 Agriculture o f 

 the University of 

 C ali fornia, at 

 Berkeley. The 

 articles are illus- 

 trated -with pho- 

 tographs and 

 drawings of the 

 various s tr uc- 

 turcs and devices 

 used in compiling 

 the data. THE 

 EDITOR. 



To be fully 

 satisfactory for 

 measuring indi- 

 vidual deliveries 

 of irrigation wa- 

 ter a device should register the total amount of water 

 passing, rather than the rate of flow. Three devices 

 of this character Dethridge, Grant-Mitchell, and Hill 

 meters have been installed at Davis and tested. A 

 fourth, the Hanna meter, is to be installed as soon as 

 available. 



The Dethridge meter is shown in Figures 19 and 

 20. It was invented by J. S. Dethridge, of the State 

 Rivers and Water Supply Commission of Victoria, 

 Australia, and has been extensively installed in Vic- 

 toria, where 5,000 are now in use. It has also been 

 used quite extensively in Xew South Wales. 



The Dethridge meter consists of a wheel or drum 

 to which projecting pieces of sheet metal are fastened. 

 The drum is placed with its axle horizontal and is set 

 so that the projecting blades are in the current of the 

 ditch to be measured. A special box is built around 

 the wheel so that all water in passing has to strike 

 against the blades. In this way the wheel turns in 

 proportion to the amount of water passing. Knowing 

 the number of revolutions of the wheel the amount of 

 water passed can be determined. 



The illustrations given show one of these wheels set 

 in a concrete box, but wooden boxes of similar form 

 can be used. The whole structure is set just below the 



turnout gate, 

 which is shown in 

 the drawing. The 

 bottom of the box 

 is curved to fit 

 the shape of the 

 wheel. About ^ 

 inch of clearance 

 is left between 

 the box and the 

 blades. In use the 

 water comes 

 against each" 

 blade and pushes 

 it around until 

 the next blade 

 strikes the water. 

 In this way the 

 space between the 

 blades i s filled 

 with water, 

 which is carried 

 through the me- 



, ter. The meter 



shown seems to have a normal capacity of 4 cubic feet 

 per second and can be crowded to carry 5 cubic feet 

 per second. This higher quantity, however, causes 

 splashing over the top of the box. The fall needed to 

 turn the meter varies with the amount being measured, 

 " inch for 1 cubic foot per second to 2^2 inches 



from 



for 4 cubic feet per second. This small required fall 

 makes the use of this meter practicable in ditches with 

 low grade. A counter is attached to one end of the 

 axle and this indicates the number of revolutions which 

 the meter has made at any time. The difference in 

 the reading of the counter at any two times gives the 

 number of revolutions the meter has made between the 

 times of reading. By multiplying this number of rev- 

 olutions by the number of cubic feet passed per revolu- 

 tion, the total quantity of water received can be de- 

 termined. It is most convenient to transfer the water 

 received into terms of acre-feet. 



If it is desired, with the Dethridge meter, to know 

 the rate at which water is being received at any time 

 it is only necessary to time the meter for one or more 

 complete revolutions and divide the quantity passed 

 per revolution by the time for one revolution. Thus, 

 if it takes 30 seconds for the meter to make one com- 

 plete turn and it is known from its rating that it passes 



*The installation of the measuring devices described in 

 this series of articles has been carried out chiefly by S. H. 

 Beckett and R. D. Robertson, irrigation engineers, assisted by 

 Roy \Yray. The tests of the devices have been made under 

 the immediate direction of S. T. Harding, irrigation engineer, 

 in charge tif irrigation investigations in Montana, temporarily 

 on duty in California, who has also prepared the reports of 

 the tests. The weir tables have been prepared by Wells A. 

 Hotchkiss. The drawings and diagrams have been prepared 

 by Stephen C. Whipple. scientific assistant. F. L. Bixby, irri- 

 gation engineer, in charge of irrigation investigations in Xew 

 Mexico, temporarily on duty in California, assisted in design- 

 ing the general plan of installation. The full study has been 



planned and. in general, supervised, and the data has been ar- 

 ranged for publication by Frank Adams, irrigation manager. 

 The installation of the Davis field laboratory, and the 

 testing of the devices have been jointly paid for from funds 

 contributed by the state engineering department of California, 

 the office of experiment stations of the United States depart- 

 ment of agriculture, and the California agricultural experiment 

 station. Co-operation with the state engineering department 

 of California has been effected through agreement between 

 that department and the office of experiment stations, the irri- 

 gation investigations at Davis having formerly been carried 

 on by those two agencies without financial aid from the Cali- 

 fornia agricultural experiment station. 



