Outline of Steps Taken in Calibrating 

 Mill Creek Standpipe 



With the information provided by the 

 references cited, a series of calibration 

 tests were run in a laboratory flume to 

 correlate dilution rate in the standpipe 

 with measured velocities of flow past the 

 standpipe (fig. 2). This is done as fol- 

 lows: 



1. In the laboratory, set up a test 

 flume of known dimensions, fill it with a 

 known mixture of sand and gravel, place a 

 standpipe in the gravel, and pass water 

 through the flume at a known rate of flow 

 in cubic inches per second. 



2. Knowing the width of the flume and 

 the rate of flow, after measuring the height 

 of water at the standpipe, compute the aver- 

 age velocity of flow at the standpipe in 

 feet per hour. 



3. Obtain a corrected velocity of 

 flow by (a.) noting the temperature of the 



water and (b) calculating what the velocity 

 would be at the "standard" temperature. 



4. Determine the volume of water in 

 the standpipe, and calculate the ratio of 

 this volume to a "standard" volume. 



5. Introduce a few drops of salt solu- 

 tion into the chamber of the standpipe and 

 note the rate at which the resistance 

 changes as the rate of seepage of water 

 through the gravel is varied. 



6. Correct the resistance readings to 

 corresponding resistance at the "standard" 

 temperature. 



7. Correct the "end" resistance read- 

 ing for the effect of "bleeding". 



8. Calculate the "displacement number" 

 by use of a chart of displacement curves. 

 The displacement number is a one to one pro- 

 gression of dilution which is associated 

 with appropriate resistance readings as 

 indicated beforeheuid by a conductivity bridge 



Figure 2. — Calibrating the standpipe in the laboratory. 



