WEIR MEASUREMENT 213 



of water over weirs, Cipoletti invented the form of weir which 

 has taken his name and which is in general use throughout the 

 irrigated sections of the world. 



The Cipoletti Weir. The Cipoletti weir has a thin horizontal 

 crest, the sides of the weir notch sloping back from the vertical 

 at an angle equal to one inch in horizontal for every four inches 

 in vertical. This, for each additional inch in depth the weir notch 

 widens on each side one-fourth of an inch, or a total addition of 

 width of one-half inch. A weir having a length of crest of one 

 foot, and designed to be eight inches in depth, will have a top 

 width of notch of 16 inches. 



When the weir box is placed, care should be taken to have the 

 bottom of the notch, or crest, level. An ordinary carpenter's spirit 

 level may be used for this purpose. When the crest is horizontal, 

 one end of the spirit level is placed on the center of the crest, 

 and when level the other end will mark the point for the zero of 

 the weir gauge. In rough work a nail may be driven part way 

 into the side of the box, the top of the nail being level with the 

 crest of the weir. A thin plate of brass is to be preferred to a 

 nail. In other cases gauges are inserted on the sides of the flumes 

 and properly marked in tenths of feet or inches. At other times 

 a post from 1 to 2 inches square is placed in the center of the box 

 and several feet above the weir board. The top of this post is on 

 a level with the crest. This is the method shown in the accompany- 

 ing sketch. 



How to Measure Water Over Weirs. The method to follow 

 can best be shown by examples. Let us suppose that a farmer has 

 made and placed a box similar to the one shown in the drawing, 

 after turning in the water and allowing it some time to attain a 

 uniform flow he proceeds to the weir box and with an ordinary 

 rule measures the depth of water flowing through the weir notch. 

 Bear in mind that this measurement is not made at the weir board, 

 but at the regular gauge, whether it be a nail, brass plate or post, 

 as already described. We will assume that the depth as found by 

 the rule is 3*/2 inches. Now by referring to the table below he 

 follows down the first column until 3 l / 2 is reached. The weir used 

 is one foot, and under the column marked "1-foot weir" and oppo- 

 site the figure 3y 2 already found he finds the cubic feet per minute 

 or the gallons per minute flowing over a one-foot weir when the 

 depth of water is 3^ inches. The equivalent flow in gallons per 

 minute for any given length of weir and depth of water over the 

 crest was obtained from the accompanying table : 



