STREAM-FLOW 



61 



For example: Suppose the weir to be 72 inches long, and the 

 depth of water over the stake to be llf inches. Follow down the 

 left-hand column of the figures in the table until you come to 

 11 inches. Then run across the table on a line with the 11, until 

 under f on top line, you will find 15.85. This multiplied by 72, 

 the length of weir, gives 1141.2, the 

 number of cubic feet of water passing 

 per minute. 



The above table will give results 

 sufficiently close for all practical pur- 

 poses, but if extreme accuracy is 

 essential the following formula l 

 might be used, in connection with 

 measurements obtained from the 

 method previously described : 



In the above L= length of weir 

 in feet, // = head or depth of flow in 

 feet over weir, as measured on the 

 stake; (?= cubic feet of water per 

 second. 



The Gurley Hook Gauge, Fig. 20, 

 is a very useful device for measuring 

 the depth of the water passing over a 

 weir. Its arrangement is such that 

 the readings can be taken by the 

 observer with the greatest possible 

 convenience and at some distance 

 from the surface of the stream being 

 measured. 



This gauge is used in a box attached to a flume at any con- 

 venient point near the weir, the water from the flume being con- 

 veyed to the box by rubber or lead pipes, thus indicating the pre- 

 cise level of the water in the flume, the surface of the water in the 

 box being at rest. The exact level of the crest of the weir should 

 be taken by a leveling instrument and rod, and marked by a line 

 drawn in the still water box at the surface of the water. The 

 1 Pelton Water Wheel Co. 



j 



FIG. 20. Gurley Hook Gauge. 



