DISTRIBUTION AT POINT OF DISCHARGE 



Dye studies showed two distinct plumes. The majority of the dis- 

 charge mixed with ambient water and sank to the bottom of the 

 canal scouring the silt from the canal wall. It fanned out to 

 form a hot, high-saline layer which spread west and northwest 

 along the bottom. At the point of discharge, a smaller portion 

 of the effluent was carried to the surface by entrained air 

 bubbles. Within 60 feet (18m) the bubbles escaped and the upper 

 plume sank to lie on top of the layer formed by the lower plume. 

 A large portion of the upper plume circulated around a group of 

 pilings adjacent to the discharge pipe and was entrained into the 

 effluent jet and carried to the bottom. 



The effluent was diluted by surface water entrained at the point 

 of discharge. Since surface water to the north of the discharge 

 pipe consisted of effluent circulating around dolphin #4, the 

 majority of ambient water that mixed with the effluent came from 

 south of the discharge, along the eastern edge of the canal. By 

 the time the effluent reached equilibrium depth it was diluted 

 approximately twenty times with ambient seawater. 



DISTRIBUTION OF THE EFFLUENT STRATUM 



The effluent, after the initial turbulent flow to the deeper water 

 of the canal, spread throughout the harbor and turning basin. There 

 was little vertical mixing and the effluent retained its heat and 

 salinity characteristics throughout the harbor to a point about 600 

 meters beyond the outer rim of the turning basin. Figure 12 shows 

 the average increment in temperature (AT) and salinity (AS) associated 

 with the effluent layer. The similar distribution of the two values 

 demonstrates the conservation of temperature in the system. Greater 

 temperature differences were found between points separated six 

 inches vertically than between points over one kilometer apart hor- 

 izontally. One rapid survey of the effluent stratum at a depth of 

 20 feet (6m) showed a temperature of 31.6°C at the inner end of the 

 canal, 31.6°C directly in front of the discharge, and 31.6°C at the 

 outer rim of the turning basin. The temperature increased from 30.6°C 

 to 31.6°C in only six inches at the stratum-ambient water interface. 



The effluent layer required constant discharge from the plant to 

 remain stable. When the plant was operating, the effluent stratum 

 was insulated in two ways." Because of the sill surrounding the harbor, 

 the upper layer of water moved out of the harbor faster during ebbing 

 tides than the lower layer containing the effluent. The most recent 

 discharge from the desalination plant was less dense than older effluent 



48 



