DETAILS OF WEIR MEASUREMENT 



185 



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 accompanying 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 



Weir box in operation showing post from which to measure depth of stream. 



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 3J/2 is reached. The weir used is one foot, and under the column 

 marked "1-foot weir" and opposite the figure 3^ already found, he 

 finds the cubic feet per minute or the gallons per minute flowing over a 

 1-foot weir when the depth of water is Z l / 2 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 : 



