THE FAEMER's short-box MEASURING FLUME. 



13 



Table 4. — Showing the per cent of error in freeflow and discharges due to various changes 



in the flume. 



Upper 

 gauge 

 head. 



Feet. 



0.400 

 .800 

 .400 

 .800 

 .200 

 .800 

 .200 

 .800 



Size of 

 flume. 



Fea. 

 1 

 1 

 1 

 1 

 1 

 1 

 1 

 1 



Size of 

 weir 

 bulk- 

 head. 



Condition. 



Inches. 



2 by 12 \Both edges of crest rounded to curve of 



2 by 12 / J inch radius 



2 by 12 ilRounded crest replaced by sharp metal 



2 by 12 1/ crest 



2 v^ 2 j I Standard crest. Auxiliary walls set 



2 hv 1^ If 'vertical at a distance of 3 inches back 



2 bv 12 ' from the sides of the flume 



Dis- 

 charge. 



Sec.-ft. 

 0.926 

 2.698 



.882 

 2.604 



.333 

 2.786 



.323 

 2.713 



Stand- 

 ard 

 experi- 

 mental 



dis- 

 charge. 



Sec.-ft. 

 0.896 

 2.686 



.896 

 2.686 



.336 

 2.741 

 1.313 

 2.686 



Differ- 

 ence. 



0.030 



.012 



-.014 



-.082 



-.003 



.045 



.010 



.027 



Error 



Per cent . 



3.3 



4 



-1.6 



-3.1 



-0.9 



1.6 



3.2 



1.0 



' Curve value, experimental discharge not determined for this head. 



SUMMARY. 



The farmer's short-box measuring flume was cahbrated 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. 



