146 



It is obvious from the diagram that the salinity (chlori- 

 nity) of the shelf water is essentially uniform from a depth 

 of 40 feet down to the approximate break in slope at the outer 

 edge of the shelf. The median value of 33,50 o/oc (CI =18.55 o/oo) 

 has been used in all computations of dilution as the value of 

 normal shelf water. Above a depth of 40 feet, the salinity 

 varies over a considerable range. This variation is due to two 

 factors. First, the effect of dilution of the normal shelf water 

 by effluents and second, reduction in the salinity of the surface 

 layer by natural runoff and precipitation, and increases in 

 salinity due to evaporation. It is obvious from an examination 

 of the curve in Figure 73 that the highest surface salinities 

 are still close to 33.50 o/oo (18.55 o/oo), indicating that 

 dilution and replacement by currents rather than evaporation is 

 the dominant factor maintaining salinities in the bay. 



The overlap of points taken from samples obtained at dif- 

 ferent times of the year indicates that there is practically 

 no seasonal variation taking place in the shelf water due to 

 dilution or evaporation. This probably means that the water 

 of the bay under natural conditions is entering and leaving 

 under steady state conditions. There is no marked variation 

 in salinity at any depth over the shelf, showing that there are 

 no locations where water stays in place long enough to be appre- 

 ciably changed by natural or man-made factors from its entering 

 state. The uniformity of the salinity value of shelf water off 

 the southern California coast is further shown by the identical 

 medijin values for shelf water obtained off Whites Point and 

 Orange County v^uring the survey period. It would appear that 



