water in the standpipe may be ascertained. 

 With the volume known, a ratio is available 

 between existing volume and standard test 

 volume, upon which laboratory measured velo- 

 cities are based. 



A weak solution of salt is introduced 

 into the chcimber of the steindpipe to obtain 

 rate of displacement from dilution of the 

 Salt solution. The difference in weight 

 between the original solution and the in- 

 flowing seepage creates vertical currents 

 within the chamber and results in mixing, 

 which is desirzible. A 0.06 percent solution 

 of Salt with a resistance reading of 1,000 

 ohms per centimeter cube allows an adequate 

 range for measuring dilution in the Sacra- 

 mento region, where resistance readings as 

 low as 7,000 ohms per centimeter cube have 

 been recorded. The rate of dilution is then 

 measured in units of 100 percent displace- 



ment. One part salt solution diluted by 

 1 part water, for excimple, is 100 percent 

 displacement. One part salt solution diluted 

 by 3 parts water is 200 percent displacement, 

 and so on. This displacement may be calcu- 

 lated by means of the following formula show- 

 ing the general relation between Y, the parts 

 of diluent, and P, the percentage of dis- 

 placement: 



Y = (2" -1), where n = P/100 



In the accurate measurement of dilution 

 by a conductivity bridge, the conductivity 

 of the diluent itself must be considered. 

 A series of 3 curves representing the range 

 of conductivities expected in the upper 

 Sacramento River area were prepared in rela- 

 tion to their respective multiples of dis- 

 placement and are represented in figure 5. 



15,000- 



14,000 



13,000 



S 12,000 



I 11,000 



5 10,000 



LP 



I 9,000 

 ] 8,000 

 7,000 

 6,000 

 5,000 

 4,000 

 3,000 ■ 

 2,000 

 1,000 



■ Zf>° 



Diluents 15,000 Ohms 



iSO, 



/ 



/ 



/ / 





/ 



/ 



/// 



//// 



/// 



y^ 



'A 



//, 



Diluents 10,000 Ohms 

 9,000_— 



e.goo — 



Diluents 7,000 Ohms 



// 



V// 



v^-^yy 



'/ 



/''/y. 



/, 



5^0 



X. 





'/^ 



— r- 

 10 



Number of Equal Volumes Added 



Figure 5. — Three curves plotted with electrical resistance readings 



corresponding to displacement units of salt solution using 

 typical diluents expected in the Sacramento River area. 



10 



