For all practical purposes, therefore, we can write 



B • 1 



Ci 1 =A(l-rA)rA + ^— ir^d-r ) r , (18) 



"ta' '^ 

 or its equivalent 



where 0.35A is the portion of the original contaminated volume A 

 which remains in section A at the end of 



1 



tidal cycles, and 



^^=t 



0.35B 

 (1-r) 

 is that portion of the total contaminant arriving from B in 



tidal cycles which would remain in A at the end of this latter time. 



If the curves 



yj =(0.35rA, m = l,2, etc. (20) 



and 



y2=(0.35)"-Y-^. n = l,2, etc. (21) 



are plotted for the same coordinates, but with unit lengths on the 

 abscissa corresponding to the reciprocals of their r-values, the 

 sum of (20) and (21) will be a curve expressing the remaining con- 

 taminant in section A after any desired number of tidal cycles have 

 occurred as illustrated in Figure 3. 



For example, let 



A equal 10 units 

 B equal 14 units 

 Q^ equal 0.4 unit 

 Qg equal 0.3 unit 



The exchange ratios are rA equal 0.04, rg equal 0.0214, and r equal 



