MEASUREMENT AND DUTY OF WATER. 



203 



to a certain extent, but not altogether satisfactorily. 

 Ignorance or carelessness on the part of prior holders 

 may result in working gross injustice by causing the 

 waste of water which would otherwise be used by 

 subsequent appropriates. 



The rate of flow (expressed in inches or otherwise) 

 does not afford sufficient data for us to compute the 

 duty of water. We should know the length and fre- 

 quency of the periods during which this flow is main- 

 tained. 



No one would think of irrigating an acre with one 

 inch of water, for it could not be spread over the 

 ground; fifty inches would be ample, yet it would be 

 used only about one-fiftieth of the time required for 

 fifty acres. In many cases fifty inches would be suffi- 

 cient for 100 acres, yet it would have to be nsed for a 

 longer period; by this time, in some localities, it may 

 be necessary to commence another irrigation. This 

 would determine one-half inch per acre during the 

 irrigating season as the flow necessary in that portion 

 of the country. 



THE MEASUREMENT OP WATER. 



In the arid region there are approximately 5,600 

 square miles of irrigated area, or about one-half of 

 one per cent of the total area of the lands within the 

 States and Territories of the United States where irri- 

 gation is commonly practiced.* Of the remaining 

 land, amounting to about 1,400,000 square miles, 1,062,- 

 000 square miles, approximately, is classed as desert 

 and pasture land. The proportion of this enormous 

 tract which can be irrigated will depend to a great 

 extent upon the thoroughness with which we utilize 

 our water supply. Careless measurement frequently 

 results in waste and injustice. 



The method of measuring water in Montana author- 

 ized by law is given as follows: 



EXTRACT FROM COMPILED STATUTES OF MONTANA. 



"Section 1262. The measurement of water appro- 

 priated under this chapter shall be conducted in the 

 following manner: A box or flume shall be con- 

 structed with a headgate placed so as to leave an 

 opening of six inches between the bottom of the box 

 or flume and the lower edge of the head-gate, with a 

 slide to enter at one side, and of sufficient width to 

 close the opening left by the head-gate, by means of 

 which the dimensions of the opening are to be ad- 

 justed. The box or flume shall be placed level, and 

 so arranged that the stream in passing through the 

 aperture is not obstructed by backwater, or an eddy 

 below the gate; but before entering the opening to be 

 measured the stream shall be brought to an eddy, and 

 shall stand three inches on the head-gate and above 

 the opening. The number of square inches contained 

 in the opening shall be the measure of inches of water." 



The Montana Society of Civil Engineers, recogniz- 

 ing the ambiguity and imperfection of this statute, 

 endeavored to have it repealed and another law sub- 

 stituted which would establish a definite quantity of 

 water flowing past a point in a given time as the 

 standard. They proposed that a cubic foot (7.48 gal- 

 lons) of water flowing in one second of time be taken 

 as the standard, and that where water rights had been 

 decreed by the courts, forty statutory inches should 

 be considered equivalent to one cubic foot per second; 

 that is a stream flowing forty statutory inches would 

 fill a vessel of one cubic foot capacity in one second 

 of time. 



* Keport on Agriculture by Irrigation, F. H. Newell. 



The objections urged by the engineers against the 

 present statute are: 



1. It is ambiguous and no accepted definition of the 

 word eddy will apply and make sense. 



2. The velocity of the approaching water may be 

 varied. If the head or height of the surface of the 

 water be measured directly over the opening and a 

 box or flume be used, there must be a certain velocity 

 of approach, even if one end of the box or flume tap 

 a lake. This velocity may be altered by altering the 

 width of the box or flume in comparison with the 

 width of the opening through which the water flows. 

 For example, if we have an opening through which 

 100 statutory inches are flowing (6 in. X 16% in.) 

 with a box or flume of the same width, a very usual 

 condition, we would have the area of the approaching 

 stream (6 in. -J- 3 in.) X 16% in. = 150 square inches; 

 100 statutory inches are equal to about 2% cubic feet 

 per second, so that the water would approach the 

 opening with a velocity of about 2.4 feet per second. 

 The theoretical value of the extra head due to this 

 velocity would be something over one inch, making 

 the actual head over the center of the opening some- 

 thing over 7 inches instead of 6 inches as apparently 

 contemplated by the law. This would increase the 

 flow about 6.4 per cent. This amount may be in- 

 creased by bringing the water to the box with an in- 

 itial velocity greater than 2.4 feet per second, or may 

 be decreased by widening the box. 



3. All measurements of head taken directly over 

 the opening must necessarily be approximations; this 

 may be a matter of little or no importance for small 

 openings, but as the difficulty in securing accurate 

 measurements increases with the size of the opening 

 there eventually comes a limit beyond which it is 

 practically impossible to measure water by the statu- 

 tory inch-box with any pretension to accuracy. On 

 an opening of 42 inches wide the surface of the water 

 over the middle of the opening is depressed about 

 % inch below the surface at the end of the opening. 



The proper place to measure the head or height of 

 the surface of the water above the opening is several 

 feet up stream from the opening, but the statute does 

 not provide for this. 



4. The statute does not provide for the measure- 

 ment of large bodies of water. A stream carrying 

 6,000 inches of water would under the statute require 

 a box 1,000 inches or about 84 feet wide. 



5. The Montana statutory inch does not represent 

 any particular quantity of water, but a quantity in- 

 creasing with the number of inches flowing. For 

 instance, where the flow is 36 statutory inches, one 

 inch is equivalent to about 15,108 gallons; but where 

 180 statutory inches are flowing, one inch is equiva- 

 lent to about 15,964 gallons. 



WEIR MEASUREMENTS. 



No device for measuring flowing water has been 

 more thoroughly tested and experimented with than 

 the weir, with the result that notwithstanding the 

 simplicity of its construction we may, by taking 

 proper precautions, determine the amount of water 

 flowing over it within one per cent. 



An idea of a measuring weir may be obtained from 

 the accompanying engraving of the Cippoletti weir. 

 The opening in this case is trapezoidal in shape, al- 

 though a rectangular-shaped opening has been per- 

 haps more frequently used. Where very accurate 

 measurements are desired, the edges of the opening 

 are made of comparatively thin metal. The amount 

 of water passing through the opening is determined 



