USE OF CONCRETE PIPE IX IRRIGATION. 



33 



Several years ago, a large number of experiments were conducted 

 by V. M. Cone of this bureau at the hydraulic laboratory at Fort 

 Collins, Colo., on the flow of water through weir notches. 4 



In figure 11 is outlined the inside dimensions of a standard weir 

 box to measure water within 1 per cent of accuracy in accordance 

 with the different volumes specified in Table 1. In Table 2 is given 

 in cubic feet per second the discharge through rectangular weirs from 



1 to 4 feet in length and for varying heads. 



Table 3 gives the percentage of error which occurs when changes 

 from the standard form are introduced. Thus the effect of side con- 

 tractions (C in figure 11) is seen in the increase in error of a 1-foot 

 weir and a 6-inch head from less than 1 per cent to 4 per cent when 

 the distance of the sides from the end of the crest is reduced from 



2 feet to 6 inches as shown in figure 12. 



Fig. 11. — Standard 18-inch weir based on dimensions given in table. 



Table 1. — Weir-box dimensions for rectangular notch iceirs. 



[All dimensions in feet. The letters at the heads of the columns in this table refer to figure 11.] 



RECTANGULAR WEIRS. 



Flow (second-feet). 



H. 



Maxi- 

 mum 

 head. 



L. 



Length 

 of weir 

 crest. 



A. 



Lsngth 

 of box 

 above 

 weir 

 notch. 



K. 



Length 

 of box 

 below 

 weir 

 notch. 



B. 



Total 

 width 

 of box. 



E.o 



Total 

 depth 

 of box. 



c. 



End of 



crest 



to side. 



D. 



Crest 



to 



bottom. 



F.6 



Hook- 

 gauge 

 dis- 

 tance. 



G.c 



Hook- 

 gauge 

 dis- 

 tance. 



J-to 3 



1.0 

 1.1 

 1.2 

 1.3 

 1.5 



1 



U 

 2 

 3 



4 



6 

 7 

 8 

 9 

 10 



2 

 3 



4 

 5 

 6 



5 \ 



7 



8i 

 12 

 14 



3J 



4 



4J 



5 



5| 



2i 

 2f 

 3i 

 41 

 5 



2 



2i 

 2| 

 3J 



3* 



4 



41 



5 



5* 



6 



2 



2to 5 



2 



4to8 



2h 



6to 14 



3 



10 to 22 



3 















* For further information the reader is referred to Farmers' Bulletin S13 on the Con- 

 struction and Use of Farm Weirs, by V. M. Cone. 



a This distance allows for about h foot freeboard above highest water level in weir box. 

 & Equals distance from crest upstream to gauge. 

 c Equals distance from end of crest over to gauge. 



