RESTRICTED 



22 



5. EFFECT OF V/EATHER ON LAGOON CIRCULATION MD DECONTAI.HNATION 



The quantitative estiioate of the decontamination rate 

 presented in the previous section required certain basic assurap- 

 tions about the weather, particularly as regards v/ind direction 

 and speed. These factors are of the greatest iciportance in de- 

 termining the circulation of the lagoon in general and the dissi- 

 pation of radioactive products in particular. The calculation 

 was based on what appeared lilcely to be the prevailing conditions 

 at the time of the blast, namely an ENE wind with a speed of 

 about 10 knots. Different conditions would require modification 

 of the predictions, and over a limited range of variations the 

 modifications can be made accurately. The effect on the lagoon 

 of winds between 10 and 20 knots is well known. The curves can 

 be extrapolated to 5 knots with no great error. These are sim- 

 ply questions as to rates of diffusion and water transport. 



The ciijrves previously shown in Figure 8 are a fair indica- 

 tion of the effect of wind on ciarrent transport. V/ith winds of 

 5 knots, the rate of flow of the surface current would be reduced 

 to 0,1 to 0,2 knot, and it v/ould require three or four days for 

 the contamination to spread the full length of the lagoon. Hori- 

 zontal and vertical diffusion would also be reduced. The east- 

 west gradient in radioactive products would be less pronounced. 

 "Upwelling of bottom water in the eastern end of the lagoon would 

 be likely to produce patches of v/ater with high concentrations 

 of contaminant for three days or more. 



V7ith a 20 knot wind on the other hand, the rate of flow 

 would be increased to 0.5 knot, and the contaminant would spread 

 across the lagoon in about one and a half days, but the east- 

 west gradient would be stronger and more persistant. 



Since the available weather data indicate a decrease in 

 wind velocity during the sumraer and a shift in the average di- 

 rection toward the east or southeast, it is barely possible that 

 the test might come at a time when these changes are extreme, 

 namely no wind or a southerly v^ind. There has been no oppoirtun- 

 ity to determine what would happen in such cases. Aay predic- 

 tions are largely speculatory, but a few general comments can 

 be made. 



It Is believed to require twelve to twenty-four hoiirs for 

 a wind driven current to be generated or for it to cease when 

 the wind stops. Therefore in a prolonged period of calm weather 

 the rotary circulation of the lagoon would soon be destroyed. 

 There would remain only the slow movements generated by tidal 

 interchange. Vertical and horizorttal diffusion would be greatly 

 reduced. It seems likely therefore that a large concentration of 



