AN OCEANOGRAPHIC MODEL OF PUGET SOUND 695 



water appeared to flow into a bottom layer below 100 meters before 

 there was any effect above that level. After 38 days, however, there 

 was more saline water at all layers with a relatively uniform gradient 

 existing between 10 and 80 meters. At this time, the salinity below 100 

 meters had practically attained its maximum value. Equilibrium con- 

 ditions were closely approached by the end of 89 days. 



It is seen from these results that, with the exception of Green Point, 

 significant salinity gradients will appear at all depths for appreciable 

 lengths of time following a change in source salinity; whereas a change 

 in river runoff will only have a minor and local effect. Qualitatively, 

 these results are borne out in the prototype. Characteristically, the Pu- 

 get Sound basins flush most rapidly in the fall when the Strait of Juan 

 de Fuca water, the salinity source, is of its greatest annual density, and 

 not during periods of maximum local runoff. 



Model Applications 



The model has been operated for groups of engineers interested in 

 sewage disposal and pollution studies with good success. The insertion 

 of dye at present or proposed sewage outfalls gives a clear and rapid pic- 

 ture of the pollution likely to occur at various localities. The value 

 of a tidal model for this type of study may readily be appreciated when 

 the ease with which a particular mass or type of water may be "tagged" 

 by a suitable dye is seen. The transport and rate of dispersion of the 

 water mass may be observed directly and continuously followed over 

 large areas for the equivalent of long periods in the prototype. 



The model has proven useful support of a fisheries-biology study 

 concerned with tiie drift of fish eggs. The drift of dye in the model 

 correlated with field observations clarified the movement of the eggs, 

 location of the hatching areas, and distribution of the larvae. Con- 

 tinuous observations were made for a period representing many days in 

 the prototype. Thus a detailed picture could be obtained from field 

 observations Avhich were somewhat scattered with respect to both loca- 

 tion and time. 



In planning field work, the model can be set to operate for the 

 anticipated period of the cruise. The probable water structure and 

 movement can be observed, and locations selected for most efficiently 

 collecting the desired information. In an area of mixed tides, a tidal 

 model which can be set to duplicate tides for a specific calendar period 

 is a distinct advantage. 



The model has proven to be a valuable teaching aid. The processes 

 occurring in nature over a large aiea are readily observable, and a 

 clear synoptic picture of their interrelations is thus obtained. Examples 



