37 



The possible role of the thermocline as a density barrier 

 to the rise of effluent -sea water mixtures is discussed in the 

 section on dilution. It would appear from field observations 

 of bacteria, nutrients, and turbidity in the neighborhood of 

 outfalls that the main importance of these thermal and density 

 boundaries lies in their effect on the position of turbid 

 layers following the initial rise of the effluent discharge 

 toward the surface. Figure 11 shows the limiting ranges of 

 water temperature in 200 feet of shelf water at which sup- 

 pression of the rising effluent may occur. 



Classification of Water Masses and Types 



It is convenient, when dealing with ocean water, to plot 

 temperature against salinity, the resulting curve being called 

 a T-S curve. A water mass is a body of water having certain 

 temperature and salinity relationships and is defined by a 

 T-S curve. The whole body of water lying over the Santa Monica 

 Bay shelf is an example of such a water mass. A water type , on 

 the other hand, is defined by a single temperature and a single 

 salinity value. Within a restricted area the horizontal distri- 

 bution of water types can be represented by surfaces containing 

 all points in a water mass having these singular characteristics, 

 In the special case of the Santa Monica shelf where the sali- 

 nities are nearly uniform, such surfaces will approximately 

 correspond to isothermal surfaces. Ordinarily, water mass and 

 water type analyses are not made for waters near the surface 

 or in shallow areas. However, in this case they have proved 

 useful. In previous reports the two basic terms sometimes 



