and 0„ 



rB= I' . (5) 



respectively. These ratios express the fraction of volume A which 

 is lost to the sea in a tidal cycle, and the fraction of volunne B which 

 passes into section A in a tidal cycle. The actual volume of mixed 

 water containing contaminant, which is removed from the estuary with 

 each ebb of the tide, is: 



Consider now the high water situation in the estuary at the end of 

 the first tidal cycle following initial contamination. The volume of 

 contaminated water removed with the first ebb tide is given by (6); 

 the contaminant remaining in section A would, therefore, be given by 



Ad-r;,) (7) 



had not the quantity 



TbB (8) 



entered section A from section B. The remaining volume of contaminant 

 in B, is: 



B(l-rB). (9) 



at the end of the first tidal cycle. 



The contaminant lost from section A during the second tidal cycle 

 is, from (7) and (8), 



r^C, = r*[A(l-r^) + rBB)], (10) 



and that remaining in section A at the time of the second high water 

 is 



C2 = [a(1 - rO + Tb B ] (1 - r^ ) + Tb B(1 - rg), 



(11) 

 where, as before, the quantity TbBCI— Tg) 



entered A along with the salt necessary to replenish that lost to the 

 sea with volume Qa- 



Similarly, for the third tidal cycle, 



