THE IRRIGATION AGE. 



169 



General view of the Davis (Cal.) Field Laboratory of Irrigation Measuring Devices. 



Besides measuring water with reasonable ac- 

 curacy, under sometimes widely varying conditions, 

 a satisfactory device for taking account of farm 

 water deliveries must be extremely simple in de- 

 sign, and be made of materials that are available 

 and inexpensive. It should at least in part be sus- 

 ceptible of construction by the farmer to be served, 

 and to be widely used, should not cost above, say, 

 from twenty-five to fifty dollars. Where all of the 

 farmers under one lateral receive the same flow of 

 water in rotatiori, each retaining it for a length of 

 time proportional to his interest in the system or 

 the number of acres he irrigates, a device that both 

 measures the rate of the flow and holds that flow 

 constant is the ideal to be sought for. While there 

 are few devices in use that hold the flow of water 

 constant, reasonably satisfactory results are ob- 

 tained under the rotation plan by measuring or 

 gauging the turnout with sufficient frequency to 

 enable its being held about uniform. Where rota- 

 tion on laterals is not feasible, or where independent 

 individual deliveries are preferred, the measuring 

 device, to be fully satisfactory, should register the 

 total amount of water passing rather than the rate 

 of the flow. While this result can be accomplished 

 by using a water register in conjunction with a weir 

 or other device that takes account of the rate of 

 flow, water registers require too much care and are 

 too expensive for use in making deliveries of water 

 to farms. The Dethridge, Grant-Michell, Hill, and 

 Hanna meters described in these articles are all of 

 the type that register the total flow rather than 

 measure the rate of flow, and to the extent that they 



can be made to meet the conditions already named, 

 are preferable to the more simple weir or orifice 

 taken singly. 



In planning and carrying out the installation 

 at Davis three main purposes have been held in 

 view: To assemble in one accessible place, and 

 largely for demonstration uses, examples of the 

 principal irrigation measuring devices so far de- 

 veloped ; to make such tests of these devices as 

 would demonstrate their accuracy under ordinary' 

 field conditions when compared to a standard weir 

 and to each other; and incidentally to furnish an 

 opportunity to students at the University Farm to 

 make practical working tests in agricultural hy- 

 draulics. In installing the various devices the effort 

 has been made to follow practical field rather than 

 ideal laboratory conditions ; also, in describing the 

 devices and the tests made of them, technical lan- 

 guage has been wholly eliminated. 



The purpose of these articles is to describe 

 fully, illustrate by drawings and photographs, and 

 point out the relative accuracy of some types of 

 the devices that have already become standard or 

 that have been in use for a sufficiently long time 

 or on a sufficient scale to make them of enough 

 public interest to warrant their installation at the 

 Davis field laboratory. This field laboratory offers 

 opportunity for the installation and testing of other 

 irrigation measuring devices, and since these articles 

 were prepared the designers of two devices have 

 made installations there for such impartial testing 

 as it is desired to subject them to. It is hoped to 

 add to the demonstration from time to time, so that 



