THE FARMER’S SHORT-BOX MEASURING FLUME. 13 | 
TasLe 4.—Showing the per cent of error in free flow and discharges due to various changes 
in the flume. ; 
- | 
| Stand- | 
i 1, ees + | | 
Upper | size of |, weir en: pis faeges | miner wet 
auge | flume. | bulk- ee charge. | mental | ence. . 
ead. | | head. | dis- | 
| | charge. | 
Feet. Feet. | Inches. Sec.ft. | Sec-ft. Per cent. 
0. 400 | 1 | 2by12 \Both eee of crest rounded to curve of e = 0. a | 0. - “ 
. 800 | Pl easyele 1 ae Pe AIS 7. -- Fe 2-2. - = back ee - i . O12 
- 400 | 1 | 2by 12 Rounded crest replaced by sharp metal { - 882 | .896 | —.014 —1.6 
. 800 | 1/)| 2by 12 CYSL- Sta 8 ae. CE bd EE 2. 604 2.686 | —.082 | —3.1 
; = | : : sta 4 |standard crest. Auxiliary walls set 9 = 2 so a i arg 
"900 | 1/2 “ah 2 vertical at a distance of 3 inches back = 393 1 313 010 39 
: 800 } 1 2 by 12 from the sides of the flume............ 2 713 2.686 027 1.0 
1 Curve value, experimental discharge not determined for this head. 
SUMMARY. 
The farmer’s short-box measuring flume. was calibrated in order 
to make possible the successful use in the distribution of water of the 
structures of this type already installed. 
The accuracy of the device is sufficient for ordinary requirements, 
but it is not to be recommended in preference to the standard types 
of weirs. 
A comparison of the experimental discharges with the computed 
discharges for the free flow and for the submerged conditions shows 
that 77 per cent of all the free-flow computed discharges are in error 
by less than 2 per cent, and that 74 per cent of all the submerged-flow 
computed discharges are in error by less than 5 per cent. 
The results show that the submerged condition should be avoided 
if possible. 
For free-flow conditions, the gauge height may be measured either 
on the crest of the weir or 1 foot upstream from it. Care should be 
taken not to confuse the readings taken at the different points, when 
using the discharge tables. 
For submerged conditions, both the upstream and the downstream 
heads must be measured. On account of the disturbed condition 
of the water, it is recommended that, in order to increase the accuracy, 
the heads be measured in stilling wells placed outside of the flume. 
The discharge formulas are not applicable for heads greater or less 
than those given in the tables and diagrams, nor for flumes greater 
than 4 feet or less than 1 foot in width. 
Changes, such as might occur in the flumes in the field, do not 
affect the discharge sufficiently to impair the usefulness of the device. 
