DUTY AND MEASUREMENT OF WATER. l6l 



■raise the headgate until the water-level stands at the 

 water-line on the slide. In adlual use the velocity of 

 the water is not a fadlor in the measurement, the 

 velocity of each ditch being brought, automatically to 

 a constant by the slide, which creates a fixed pressure 

 for all quantities of water. 



A Simple Method of Measuring Water. — 

 Seledl a place in the stream with as even grade as pos- 

 sible having uniform banks and free from rubbish, 

 such as stones, grass or brush. It is desirable to have 

 an even fall of the stream and a nearly uniform current 

 throughout its entire width and depth. The stream 

 should have a straight course for twenty to fifty feet. 

 The cross-sedlion multiplied by the velocity or rate of 

 movement will give the approximate amount of water 

 flowing in the stream. The cro.ss-se(5tion is found by 

 measuring the depth at regular intervals across the 

 stream. The average of these is obtained by adding 

 them together and dividing by the number of measure- 

 ments taken. The average depth then multiplied by 

 the width will give the cross-sedlion. To find the 

 velocity, measure off a convenient distance, say, twenty 

 feet of the stream, where the channel is straight and its 

 bed even. Throw a chip in the stream ten feet above 

 the upper mark. The float will attain the velocity of 

 the water by the time it reaches the first mark. When 

 the float pavsses the upper point the time is noted by 

 the second-hand of a watch. The float is followed 

 down-stream until it passes the lower mark at the end 

 of the twenty feet, when the time is again noted. 



Suppose it took ten seconds for the float to travel 

 the twenty feet, then in one second the stream would 



