DEPARTMENT BULLETIN 1110. 



The discharge values computed from Formula I agree very closely 

 with the experimental data, except for heads of less than 0.2 foot. 

 Formula II, however, which gives the submerged-flow discharges, 

 does not give values that agree so closely with the experimental 

 data. This is partly due to the variation in the observed discharges 

 caused by the uncertainty of obtaining the true gauge heights. 

 Formula II, like Formula I, does not give accurate results for heads of 

 less than 0.2 foot. The agreement of the discharges computed from 

 Formulas I and II for the free flow and submerged conditions, 

 respectively, with the experimental discharges for the same con- 

 ditions, is shown graphically in Figure 3. The percentages given in 



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PER CENT DEVIATION 



Pig. 3. — Deviation of the computed data from the experimental data for free flow and submerged conditions. 



each case represent the deviation of the computed data from the 

 experimental data. These diagrams indicate clearly that where 

 accuracy is required the submerged condition must be avoided. 



FREE-FLOW DISCHARGE TABLE. 



Table 2 gives the free-flow discharges, in cubic feet per second, 

 per foot in width of flume, for various heads and heights of weirs, 

 computed from Formula I. The head at the upper gauge, which is 

 used in the formula for computing the discharge, is given in both feet 

 and inches at the left of the table. These values should be used to 

 find the discharge in the table when the head is measured at the upper 

 gauge point. If the head is measured on the crest, then the values 

 in inches in the column to the left of the discharge column for the 

 particular height of weir in question should be used. It will be noted 



