in the laboratory. 



9. By use of the ratio determined in 

 step 4, correct the displacement number 

 found in step 8 to a displacement number 

 relative to the standard volume. 



10. Correlate the displacement number 

 obtained in step 9 with the average velocity 

 obtained in step 3. 



Explanation of Steps Taken in 

 Calibrating Mill Creek Standpipe 



To obtain a good correlation between 

 Salt dilution in the standpipe and seepage 

 rate in the test flume it is important to 

 measure features of the test precisely and 

 in the manner suggested. An illustration 

 of the flume used in the laboratory is 

 shown in figure 3. The materials through 

 which the water flows are held in place by 

 fine Screening. Head and tail pools pro- 

 vide normal flow through the gravel. An 

 overflow drain pipe discharges water from 

 the tail pool. A closed system adapted 

 for recirculation of water provides water 

 similar to that found in the upper Sacra- 

 mento River. As has been pointed out by 



Professor Hermes i' the difference in level 

 between the head pool and tail pool does 

 not necessarily represent the hydraulic 

 gradient in the flume and may give rise to 

 an erroneous measure. The drop in elevation 

 is measured by comparing the upstream pool 

 level and the level of water in a well 

 located in the aquifer material adjacent to 

 the downstream pool . 



In tests conducted in the laboratory, 

 various combinations of small gravel cind 

 coarse sand are used as aquifers. Jones 

 (1954) has found that if less than 20 per- 

 cent gravel is mixed with sand, the mixture 

 is less permeable to water than is sand 

 alone. If more than 20 percent gravel is 

 mixed with the sand, however, the permea- 

 bility increases, and the rate of increase 

 is especially rapid above a content of 



1/ Personal communication from R. G. 



Hennes, Professor of Civil Engineering, 

 University of Washington. Professor 

 Hennes points out that there is usually 

 a steep gradient at the lower end of 

 the flume, as indicated in figure 3. 



Scree 



Tail 

 Pool 



Well for measuring H/L „. , . 

 / /Standpipes 



\ 



7^ 



/Grovel S Sand 





J - 



Overflow pipe 



Screen, 



Head 

 Pool 



Storage Tank 



^ 



Recirculating pump 



L - Length of drop section 

 H = Height of drop 



Figure 3.--Diagreira of test flume in laboratory. 



