1136 
Journal of Agricultural Research 
Vol. V, No. 24 
rately enough to warrant any great refinement of the discharge formula. 
The assumption of straight-line logarithmic formulas is within 1 or 2 
per cent of all the discharge data, with the exception of a few high and 
low heads; and since this is comparable to the accuracy expected under 
field conditions, such formulas were used to avoid more complicated 
equations. 
The equations of the average straight lines through the plotted points 
are given in Table I, Nos. 30 to 34, inclusive. The exponent and coeffi¬ 
cient values for these individual equations were then plotted against the 
weir crest lengths, as shown in figure 15. For simplicity the law of the 
>=>z.>w 
„ Top of canal bank 
Canal grads 
'Canal grade &C£M77C?a/ mo c 
Concrete floors and walls 6” thick 
Fig. 16.—Plan, elevation, and section (standard) of new irrigation weir box. 
coefficient values was assumed to be represented by the equation 
c — (3*83 ~ 0.07L). The exponents, with the single exception of that 
for the 1.5-foot weir, fell on the straight line which has the equation 
n= (1.52 + 0.01L). By substituting these expressions in the fundamental 
formula, Q — cLh n y the general formula for the new irrigation weir was 
obtained 
(3.83-0.0 yL)Lh^ 2+0M ^ 
The straight-line curves drawn in figure 14 for each length of weir 
represent discharge values computed from the above formula and show 
graphically the agreement of the formula with the experimental data. 
The computed discharges are given in Table II. 
