246 



THE IRRIGATION AGE. 



tions (as well as other types of 

 weirs), measurement with a 

 weir only involves measuring the 

 depth of water over the weir 

 crest and reference to the ap- 

 propriate table to determine the 

 quantity passing for the given 

 depth and crest length. 



The Cipolletti weir, as in- 

 stalled at Davis, is shown in fig- 

 ures 12 and 13. The length of 

 weir and size of box to make are, 

 of course, dependent on the quan- 

 tity of water to be measured. In 

 general, it may be said that a 

 Cipolletti weir should he small 

 enough so that the amount of 

 water to be measured will never 

 give less than a depth of one 

 inch over the weir 



A Cipolletti weir and a ITanna meter in 



crest, and large 

 enough so that the 

 depth will never 

 ineed to be much 

 more than one- 

 third of the crest 

 length. Care should 

 also be taken to see 

 that the weir crest 

 is long enough so 

 that the water can 

 be measured with- 

 out raising it high- 

 er over the weir 

 crest than is per- 

 mitted by the avail- 

 able fall. A num- 

 ber of other condi- 

 tions are usually 

 laid down as neces- 

 sary for the weir. 

 The most impor- 

 tant of these, brief- 

 1 y paraphrased, 

 follow : 



1. The distance from the crest 

 of the weir to the bottom of the canal 

 or floor of the weir box should be at 

 least three times the depth of water 

 on the weir. That is, with an 18-inch 

 weir intended to measure up to 2 cubic 

 feet per second, which requires a 

 depth on the weir of about 6 inches, 

 the crest of the weir should be about 

 18 inches above the floor. 



2. The distance from the ends 

 of the weir crest to the sides of the 

 weir box should be about twice the 

 depth of the water on the weir, or, 

 say, from 10 to 12 inches in the case 

 of an 18-inch weir measuring about 2 

 cubic feet per second. 



3. The bottom and sides of the 

 weir notch should be beveled on the 

 down-stream side to give a narrow 

 edge. The use of a galvanized iron 



crest is quite common and very satis- Fig. 14 A weir without end contractions. 



Fig. 13 Drawing of a Cipolletti weir. 



factor}', but not necessary. 

 Sometimes thin pieces of strap 

 iron are fastened on the up- 

 stream side of the weir notch. 

 In other cases the board in which 

 the weir notch is cut is merely- 

 bevelled down to a crest thick- 

 ness of one-eighth or one-quar- 

 ter of an inch. 



4. Water should not be al- 

 lowed to approach the weir with 

 a velocity exceeding 6 inches per 

 second. Also, it should flow to 

 the weir in a smooth stream free 

 from eddies or swirls. Both of 

 these conditions are most easily 

 met by placing the weir in a 

 straight section of the ditch. 



5. The water passing over 



the weir should, if 

 possible, have a 

 free over-fall. 

 \Yhere necessary, 

 however, it may 

 rise to the level of 

 the weir crest 

 without appreci- 

 able error in the 

 measurement. 



6. The depth 

 of water on the 

 weir crest must be 

 measured suffi- 

 ciently above the 

 weir to be free 

 from the down- 

 ward curve of the 

 water as it passes 

 over the weir. For 

 con v e n i e n c e in 

 making this meas- 

 urement of depth a 

 stake with its top 

 level with the crest 

 of the weir is usually set at one side 

 of the ditch 2 or 3 feet above the weir, 

 the measurements of depth then be- 

 ing made from the top of this stake 

 to the top of the water. 



The tables accompanying this 

 article give the discharge over Cipol- 

 letti weirs from 1 to 5 feet long. For 

 lengths of from 1 to 2 feet the length 

 of weir crest is given in inches and 

 the depths in inches and feet (Table 

 1 ) . For weirs with crest lengths of 

 3, 4 and 5 feet the lengths and depths 

 are given in feet only (Table 2). If 

 it is desired to measure the discharge 

 in inches instead of cubic feet per 

 second, multiply the cubic feet per 

 second given in the table by 50, if the 

 old customary Californian miner's 

 inch is desired, or by 40, if it is de- 

 sired to use the statute miner's inch 

 of California. 



The bill of material given below 

 (Continued on page 2.50) 



