depth of the effluent stratum at all stations separately. These 

 data are combined for a graph of the total average effluent depth 

 in Figure 11. The effluent layer became shallower during the study 

 as its strength, measured by the difference between the effluent's 

 temperature and salinity and the surface water temperature and 

 salinity, decreased. Figure 13 shows the average monthly location 

 of the top of the effluent stratum at various stations. The top of 

 the layer was shallowest at Station 1 and became continually deeper 

 out to the stations in the turning basin (Stations 7 and 9). At 

 Station 8, located seaward of the turning basin in the approach 

 channel, the effluent was occasionally detected flowing out along 

 the bottom at a depth of 17 feet (5.2m). 



Ambient salinity and volume of effluent discharge apparently con- 

 trolled the depth and intensity of the effluent stratum. Of all 

 parameters measured, ambient harbor salinity showed the closest 

 similarity to effluent depth when the two plots were compared 

 (Fig. 11). 



Total hours of sunshine per month are also plotted in Figure 11, 

 along with the mean difference in salinity (AS) between the surface 

 water and the effluent stratum. The two plots are more similar than 

 those of solar radiation and ambient salinity, particularly in 

 September, 1970. Hours of sunshine are, of course, related to the 

 amount of evaporation on the shallow flats adjacent to Safe Harbor 

 and the consequent changes in salinity. Water from these tidal 

 flats mixed with the effluent discharged near the surface to form 

 the submerged effluent stratum. 



The effluent stratum received little contribution from freshwater 

 run-off along the Safe Harbor shoreline. Consequently, increases 

 and decreases of AS closely approximated the shallow flat salinity 

 and solar radiation, as well as salinity changes during periods of 

 high rainfall. During heavy rainfall the effluent layer was rapidly 

 diluted by low salinity water entrained at the surface and within 

 about two hours, the upper surface of the effluent stratum began 

 moving shallower; first, near the point of discharge then gradually 

 farther along the canal. 



Differences between temperatures (AT) at 2 to 4 feet (0.61 to 1.2m) 

 and of the effluent stratum closely followed ambient temperature. 

 As the ambient water temperature decreased, so did the difference 

 between the effluent layer and the water above it (Fig. 11). Figure 

 14 shows the monthly variation of AT at each station for one year. 

 The lower AT values and shallower position of the effluent layer at 

 Stations 1 and 8 indicate these were areas of mixing. 



The Westinghouse Thermister array provided instantaneous measurement 

 of the isotherm distribution in Safe Harbor canal (Figs. 15 and 16) 



52 



