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estuaries), tidal cycles, effects of wind stress, effects of upstream 

 reservoir management, of flow quantity and quality, measurements of 

 direction and magnitude of water masses, and of velocity relationships. 



Flushing characteristics 



Closely related to a knowledge of the flow characteristics of an estu- 

 ary is a more detailed knowledge of its flushing characteristics. 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 nonconservative materials. Many of the nutrient 

 chemicals become trapped in the biomass distributed throughout the 

 estuarine zone and, thus, nutrients may not be flushed as would be 

 predicted 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 par- 

 ticles and not be passed out into the ocean. This provides a reservoir 

 of undesirable materials which, as discussed earlier, may become re- 

 introduced into the water mass or the biotic compartments. These 

 caveats notwithstanding, an accurate and quick way of determining 

 flushing characteristics of an estuary would still be extremely valuable. 

 Adequate methods of quickly determining flushing are imperative be- 

 fore any other studies can be meaningfully undertaken, because all 

 estuarine characteristics are regulated to some extent by flushing. 



This approach leads naturally to a classification of estuaries by 

 type describing flushing rates as a definition of salinity patterns, mix- 

 ing rates, and extent of salt water intrusion. The true value of all this 

 would be to develop predictive capability of estuary flushing which, in 

 turn, will yield understanding of what will happen to introduced 

 wastes and of the assimilative capacity of the receiving waters. Such 

 predictions, if reliable, are important in an estuarial water quality 

 management program. Further investigation of the feasibility of this 

 should be encouraged. 



Mixing and transport processes 



Mixing and transport processes are important aspects of estuarine 

 hydraulics. A considerable amount of research on diffusion and dis- 

 persion of wastes has been done and a body of knowledge appears in 

 the literature. Many feel that research in these areas has generally 

 fallen into two classes. It has either been too descriptive to permit the 

 transfer of specific knowledge to other estuarine areas or it has con- 

 sisted of a highly complex and idealized mathematical solution that 

 cannot be applied reliably to another estuarine area. Although the 

 technology for predicting probable water quality effects in fresh- 

 water streams has advanced to the point where predictions can be 

 made with some degree of reliability, the same circumstance does not 

 exist for estuarine areas. Applied research to develop practical predic- 



