Measurement and Division oe Water. 5 
rectangular weir is that its discharge is proportional to the length. 
This is a great convenience in the practical operation of a canal, 
with many suspicious consumers, who do not understand the facts 
of hydraulics. It avoids the attempts to explain the effect of end con¬ 
tractions called for in the rectangular weir, and the difficulty found 
by the ditch riders to do this helped to increase suspicion rather than 
inspire confidence. 
It should also be clearly understood that there is no one form of 
opening which is intrinsically better than another. There may 
be many other forms with accuracy as great or equal to the rect¬ 
angular weir. At present, however, the rectangular weir has been 
subjected to experimental tests under so many conditions that its 
peculiarities are well known and this is true only to a limited 
extent of other forms. The flow of water over weirs has 
been most rebellious to theory. But as their discharge has 
been measured under different conditions, and the require¬ 
ments for placing are so simple they can be established with 
confidence in the accuracy of the results. Tests have been made 
in such number that more confidence can be felt in it than in any 
other form of opening, and hence, while the knowledge of other 
forms may be increased in the future and thus other forms of 
opening come into use, some form of weir is the one best worthy 
of confidence at the present time. In this bulletin the triangular 
notch is also shown more at length. It is capable of use for small 
laterals and has some advantages over the rectangular weir for that 
purpose. The conditions for placing it are the same as for the 
weir, and tables are newly calculated for the discharge. The ad¬ 
vantage of the triangular notch over the weir is that only one 
measurement is necessary—that of the depth—while in the case 
of the weir, both the length and the depth need to be measured. 
The triangular notch is not adapted to large quantities of water, 
but inasmuch as one with a depth of one foot will discharge over 
two cubic feet of water per second, it gives as much as most indi¬ 
vidual laterals call for, and therefore can be used on ditches as 
distributing weirs, where the rectangular or trapezoidal weir is 
used on the larger lateral or main canal. 
The importance of measurement, both to the community and 
to the public wealth, scarcely needs mentioning. Where water has 
been plentiful in the streams and ditches, as was the case in the 
beginning, the necessity for close measurement was not felt, for 
there has been water enough for all but with greater demand for 
water, with the pressing necessity to make every drop available, 
and with the increase in the value of water, we are led to consider 
more efficient means of measurement and distribution. This is the 
history of the development of every irrigated community from 
