VI-141 



Flushing Characteristics 



Closely related to a knowledge of the flow characteristics 

 of an estuary is a more detailed knowledge of its flushing char- 

 acteristics. It appears that we know very little about the 

 true flushing time of many of the contaminating conservative 

 materials which are in solution. We, of course, can make use of the 

 freshwater-saltwater relationship to arrive at some estimate of 

 flushing time, but, it is extremely doubtful whether information so 

 derived applies to nutrients or such materials as pesticides or 

 other non-conservative materials. Many of the nutrient chemicals 

 become trapped in the biomass distributed throughout the estuarine 

 zone and, thus, nutrients may not be flushed as wpuIH be predic- 

 ted from a knowledge of the behavior of the water mass. The same 

 thing can happen with pesticides. For example, studies on the 

 Mississippi River tend to indicate that pesticides are complexed 

 onto sediment particles which then settle to the bottom, resulting 

 in a very high level of pesticides near where sediments build up 

 and a fairly low level in other areas. In other words, in a bay 

 or estuary, pesticides and other compounds may tend to be trapped 

 on sludge or sediment particles and not be passed out into the 

 ocean. This provides a reservoir of undesirable materials which, 

 as discussed earlier, may become reintroduced into the water mass 

 or the biotic compartments. These caveats notwithstanding, an 

 accurate and quick way of determining flushing characteristics of 



