(7) The Model . The existing James River model (see Fig. 3-48) 

 was ijsed for this study; model scales were 1:1,000 horizontally and 1:100 

 vertically. The model was operated by WES personnel; the data were 

 collected and analyzed by Pritchard-Carpenter, Consultants. 



(8) Test Procedures . Two series of model tests were conducted 

 to define the extent of the thermal plumes from the station in order to 

 determine whether the discharge point should be on the upstream or down- 

 stream side of the island. The water temperature observations made in the 

 physical model were adjusted analytically (Pritchard, 1967) to correct for 

 the difference in surface heat exchange coefficients between model and 

 prototype and wind effects (which were not reproduced in the model). 



One of the main purposes of the first series of tests was to deter- 

 mine the degree of mixing produced by discharging the condenser cooling 

 water as a jet having an initial velocity equal to or larger than the 

 tidal velocity in the estuary. On the basis of these studies, it was 

 determined that a discharge velocity of 6 feet per second would be most 

 suitable for design of the condenser discharge structure. 



Tests were conducted during this series with a simulated heat rejec- 

 tion at the condensers of 5.2 x 10^ British thermal units per hour, cor- 

 responding to a single 850-megawatt unit, and at 12 x 10^ British thermal 

 units per hour, corresponding to a total of 1,764 megawatts electrical 

 power production. Temperatures in the model were measured using a rapid 

 response thermistor bead mounted on a motor-driven trolley structure which 

 ran across the model on a 16-foot-long aluminum bean. A single run con- 

 sisted of setting the beam across the model at a designated cross section, 

 and running the thermistor sensor across the model to obtain a plot of 

 temperature versus lateral distance made on a strip- chart recorder. At 

 each location, runs were made each 1.5 hours throughout a tidal cycle. 

 During the July test series, a total of 496 temperature runs was made. 



For the second test series, improvements were made in the temperature 

 measuring system so that two thermistor bead sensors were towed across the 

 model on each run. The sensors were placed 18 inches apart, representing 

 a prototype distance of 1,500 feet. Near the discharge structure, one run 

 provided data for two adjacent temperature cross sections. Farther away 

 from the discharge, where the horizontal temperature gradients were small, 

 the two simultaneous sections provided a check on the consistency of the 

 data. About 489 temperature runs were made, each consisting of at least 

 one (and in many cases two) record of surface termperature across a 

 section of the estuary. 



In a special test to determine the surface heat exchange coefficient 

 for the model, Cobham Bay was blocked off from the rest of the model by 

 a long rubber dam. Motor-driven paddle wheels were mounted in the en- 

 closed area to circulate the water at a speed corresponding to the mean 

 tidal current. Thermistor bead temperature sensors were placed at sev- 

 eral locations in the enclosed water area. Water from this area was cir- 

 culated through the heaters until the temperature in the enclosed area 



84 



