DUTY AND DIVISION OF WATER 353 



213. The Cippoletti weir. The sides of the notch of 

 the Cippoletti weir slope outward at the rate of 1 inch 

 horizontally, to 4 niches vertically. The notch of the weir 

 is always made with a beveled edge of 30 or more down 

 stream so that the water always flows over a sharp edge. 

 To maintain the sharp edge, the weir should be faced on 

 the inside, or up stream, with iron strips, placed even 

 with the beveled edge. The distance from the bottom of the 

 weir box to the top of the 

 crest should be at least 

 two tunes the depth of 

 the water flowing over 

 the crest. The weir 

 should be installed where 

 the approach of the water 

 is straight, long and level. 

 As the water passes over 



the crest, it should flow ^ 98 appoletti 



very slowly, not more 

 than 6 niches a second for a weir 6 feet wide. The weir 

 must be placed at right angles to the stream, with the crest 

 absolutely horizontal. Provision should also be made for 

 washing out the accumulating sediment by making the 

 weir movable, so that it may be raised from time to time. 

 In many rivers or large canals the weirs are movable and 

 are kept above the stream except when measurements are 

 taken. Below the weir, where the water falls over the 

 crest, there should be sufficient depth, so that the water 

 below the weir does not interfere with the flow over the 

 crest. There should always be a free circulation of air 

 under the jet of water falling over the weir. When a weir 

 of known crest length has once been installed, it is neces- 

 sary to determine only the depth of water above the 

 w 



