45 



20°F, but as noted previously, the spread in temperature in 

 any given locality never approaches this extreme value. A 

 reasonable local figure for seasonal differences would be of 

 the order of 12° to 15°F. 



As a thermal entity, the Sewage Field Sub-unit is clearly 

 defined on charts of surface temperature in the winter, and it 

 appears to occupy a relatively small area around the outfall. 

 In the summer, it is not as well defined because solar heating 

 has raised the temperature of the surrounding areas to nearly 

 that of the sewage field. In summer, therefore, surface tem- 

 perature charts may not be adequate to delineate the extent 

 and position of the field. 



The Subsurface Water Unit is of relatively constant 

 temperature, the maximum range within the bay as a whole 

 being no more than 6°F. The most typical temperature seems to 

 be 53°F, and the greatest variations appear to be due to the 

 intrusion of water of slightly different thermal characteristics 



Figures 11 and 13 illustrate the differences in tempera- 

 ture between the surface and 200 feet in shelf water as a whole. 

 The maximum and minimum temperatures at 200 feet are also 

 indicated. The differences are greatest in those months when 

 the surface temperatures are highest. It is evident that 

 density distributions must follow the same seasonal pattern, 

 and that the greatest temperature drops at thermoclines or 

 gradients occur in the summer and early fall months coincident 

 with periods of greatest surface temperatures. 



