and their results are adequate to evaluate the long-term response of the 

 salinity regimen to variations in freshwater inflow. 



Salinity can be determined either by laboratory analysis (titration 

 or conductivity) of samples taken from the estuary or by in situ measure- 

 ments with conductivity or inductance meters. In the latter case, some 

 physical samples must also be obtained to ensure that the meter calibra- 

 tion remains stable throughout the survey period. 



(6) Freshwater Inflow . Freshwater inflows (mean daily flows) 

 from all tributaries to the estuary must be determined for about 2 weeks 

 before and during the velocity and salinity survey. Inflow data are also 

 required during long-term salinity observation programs, but in this case 

 mean weekly flows may be satisfactory, depending on the inflow and the 

 estuary volume. During low freshwater discharge periods, very small 

 individual discharges (e.g., industrial discharges of well water) may 

 become a significant part of the total freshwater inflow and should be 

 monitored. 



(7) Dye Dispersion . Although field dye-dispersion tests have 

 not generally been used for model verification, the tests should be done 

 if dye-dispersion tests are conducted in the model. A fluorescent dye 

 should be released continuously over a 2-week period or preferably, until 

 a stable dye regimen is established throughout the estuary. Thus, it 

 should be made during a period of relatively uniform freshwater inflow, 

 and may require a continuous release for 6 weeks or more. Data analysis 

 will be complicated by dye decay, etc., during such a long period. The 

 dye should be released at a location about two-thirds the distance from 

 the entrance to the upper limit of the model. Dye concentrations should 

 be determined at surface and bottom at numerous stations located through- 

 out the estuary. The velocity and salinity station locations may be 

 satisfactory, although additional stations along the channel centerline 

 may be desirable. The concentrations should be determined at the times 

 of local high and low water slack at daily intervals during the period 



of rapid dye buildup, but the sampling frequency can be reduced to inter- 

 vals of 3 to 7 days during the latter stages of the test. 



(8) Heat Dispersion . If tests are made of the heat dispersion 

 from an existing powerplant, water temperatures should be monitored in 

 the field for use in model verification. Surface temperatures should be 

 measured on several ranges across the plume at about 1,000-foot intervals 

 both upstream and downstream from the discharge point, and vertical tem- 

 perature profiles should be obtained at several stations in the survey 

 area. The survey coverage should be sufficient to identify the limits 



of the 0.6' Celsius (1° Fahrenheit) temperature rise contour. At leas't 

 one station should be located outside the thermal plume upstream from the 

 discharge point and one station downstream to define the ambient water 

 temperature. In designing the layout of the field survey stations, it is 

 helpful to first obtain infrared aerial photos of the area to determine 

 the size and shape of the thermal plume. Similar aerial photos should be 

 taken during the actual survey to obtain a better synoptic view of the 



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