-^ 18 - 



to form a homogeneous vertical mixture and are so vigorous that they 

 also carry bottom silt upward in sufficient quantities to maintain 

 a high degree of turbidity. In order to reproduce these effects 

 in a model it is necessary to reduce the work to be done by the 

 existing turbulence and associated eddy diffusion. The work to be 

 done is lessened by reducing the density difference enpirically 

 by an amount roughly equivalent to the vertical distortion. The 

 necessary change of density difference was actually found to be 

 about two orders of magnitude 4 This factor reduces the initially 

 small density difference (0.012) to such an uncontrollably small 

 magnitude (0,00012) that the desired condition is more reliably 

 represented by a homogeneous system. Thus the small volume 

 (165 cc/min, ) required for the rainfall contribution was pumped 

 from the very large Gulf of Mexico volume and piped into the Little 

 Lake equivalent box attached to the northwest corner of the model. 

 This method of closing the rainfall circulation produced less than 

 1 part in 2000 error in the tidal circulation and automatically 

 maintained a constant mean sea level. 



In the second case, that of the bleed water density scaling, 

 the volumes are insignificant compared with the tidal exchange of 

 the waters they enter, and as bleed water is heavier than the 

 ambient water it tends to sink. While bleed water is about as 

 much heavier than the ambient water per unit volume as the rain 

 water is lighter, and could also be well approximated by a homo- 

 geneous fluid, it was considered a more conservative approach if 



