148 



the shelf water is a well -mixed mass having its origins out- 

 side of the area of investigation and remaining essentially 

 uniform along much of the southern coast due to the absence 

 of large rivers or streams which, if present, would tend to 

 cause a progressive dilution. The only variations are restricted 

 to surface changes due to evaporation and dilution. 



Dilution from Salinity Data 



The principal area of diluted sea water in Santa Monica 

 Bay surrounds the terminus of the Hyperion outfall. This field 

 is the result of the mechanical diffusion of effluent into 

 normal shelf water at depths of 40 to 60 feet at the outfall 

 terminus, and subsequent eddy diffusion. Secondary areas of 

 dilution occur at the mouth of Ballona Creek and at the mouths 

 of the various creeks draining the Santa Monica Mountains during 

 the rainy months. The water discharged from the Edison plant 

 is shelf water and no noticeable change in salinity results. 

 These latter areas are of little importance. 



The zone that is recognizably diluted is almost always 

 confined to the upper 10 to 20 feet of the water in the bay. 

 It normally ranges in salinity from 31,80 o/oo to 33,42 o/oo, 

 as is shown in Figure 72. 

 The Effect of Dif fusers on Dilution 



It has been observed during the course of the survey that 

 effluent tends to form a column which mainly rises to, or close 

 to, the surface. In shallow water, as at the Hyperion and 

 Orange County outfalls, the individual ports (Hyperion) or the 

 terminal port produces a rising turbulent column containing 



