the plume, as defined by at least a 4°F (2.2°C) 

 temperature rise in water temperature, encoun- 

 tered both the surface and bottom thermistors 

 (Fig. 6), usually at the time of max ebb and low 

 slack. Deviations from this general pattern (e.g. 

 the period 54-66 hours from start) were probably 

 the result of a shift in wind direction (Fig. 7), 

 however neither the surface nor bottom thermistor 

 recorded temperature increases larger than 6°F 

 (3.3°C). At the other extreme, during deployment 

 #4, the data loggers experienced no temperature 

 increases of 4°F (2.2°C) (Fig. 6), although they 

 did record 1.5°F excursions. Surface water tem- 

 peratures recorded during deployment #6 in- 

 creased almost 4''F (2.2°C) just after the time of 

 high slack, presumably just as the tide turned, 

 and again just before low slack, if the winds were 

 southerly (Fig. 7). Both surface and bottom 

 thermistors experienced increased water tempera- 

 tures just after the time of high slack during de- 

 ployment #1. Also during this deployment, sur- 

 face water temperature excursions were usually 

 4°F (2.2°C) or greater; bottom water temperatures 

 usually increased less than 4°F (2.2°C). The tem- 

 perature records from deployments #2 and #7 

 were nearly identical. During both of these de- 

 ployments, only the surface probe experienced 

 brief temperature increases of 4°F (2.2°C) or 

 greater. These excursions were typically bimodal. 

 The first increase occurred at or just after the 

 time of high slack and may have represented 

 warmer water from Jordan Cove passing the 

 probe. The second peak occurred just before low 

 slack, presumbably at or just after the time of 

 maximum ebb and probably represented the 

 MNPS effluent. During deployment #5, warmer 

 water encountered the data logger for longer pe- 

 riods of time than when they were set at locations 

 farther away; temperature excursions rarely ex- 

 ceeded 4°F (2.2''C). During all deployments, 

 slight descrepancies from the general patterns just 

 described were, very likely, the result of shifting 

 wind patterns (see Fig. 7). 



Comparison of results to predictions 



The configuration and extent of the thermal 

 plume as measured by dye concentrations during 

 each tidal stage surveyed on 26 August 1987 were 

 similar to those predicted (Fig. 8). In general, 

 the area encompassed by the 4°F (2.2°C) isotherm 

 was within 10 acres of the predicted area deter- 

 mined from average conditions and was always 

 less than the area predicted under extreme condi- 

 tions (Table 5). Further, the distances to the 4°F 

 (2.2°C) isotherm also tended to be similar to the 

 average three-unit predictions and less than the 

 extreme predictions (Table 6). Because the ther- 

 mal plume predictions were meant to be conser- 

 vative and because the conditions during the sur- 

 vey were ideal, the measured plume should have 

 been smaller than predicted. 



The measured and predicted plumes were most 

 discrepant during the low slack survey (Fig. 8, 

 Tables 5, 6). The actual start of this survey was 

 about 15 minutes after the time of low slack 

 rather than about an hour before low slack as 

 was intended (Fig. 5). Thus the plume portrayed 

 as 'low slack' was probably influenced by increas- 

 ing flooding currents. However, as indicated pre- 

 viously, the low slack configuration was still 

 within the areas and distances predicted. 



The data from the seven temperature probe de- 

 ployments also supported the conclusion that, al- 

 though the actual three-unit plume is highly dy- 

 namic, it generally conformed to the predicted 

 configuration. For example, temperature records 

 from deployments #5 and #3 indicated the absence 

 of the plume during high slack, which was the 

 predicted situation. Temperatures recorded during 

 deployments #1, #2, #4, #6 and #7 indicated that 

 the plume (4°F above ambient), reached White 

 Point for short periods of time during max ebb 

 and low slack. Again, this situation was predicted, 

 although it was not observed during the dye sur- 

 vey. 



Hydrothermal Studies 343 



