DYNAMICS OF LAKES 



could arise, at least on particular days 

 in the year, when the thermal plume 

 from an electric power station would 

 travel along the shore for a long dis- 

 tance with relatively little dilution, 

 rather as a plume from a smokestack 

 is visible for miles when there is a 

 temperature inversion in the atmos- 

 phere. 



Evaporation — Although we have 

 emphasized the local, near shore ef- 

 fects and minimized those offshore, 

 there is one whole-lake consequence 

 of larger thermal additions. This 

 emerges when we consider the final 

 fate of the added heat. A large part 

 of it will be used in increasing evapo- 

 ration above the natural level, al- 

 though some will, of course, be lost 

 by back-radiation and heat exchange 

 with the atmosphere. 



If we make the worst assumption, 

 from the point of view of water con- 

 servation, that all the heat is lost 

 through increased evaporation, the 

 estimated power dissipation in Figure 

 VIII— 13 can be translated directly into 

 water loss. Tabulated as centimeters 

 of water lost from the whole lake sur- 

 face per year, the loss rises to 1.63 

 centimeters, or about l/20th of a 

 foot, in 1990. Integrated over the 

 whole lake surface, this is an impres- 

 sive volume and, in fact, represents 

 about 2 percent of the mean outflow 

 of Lake Michigan, which is 46,000 

 cubic feet per second, and about 2 

 percent of the estimated annual na- 

 tural evaporation. Some of this will, 

 of course, be returned to the lake by 

 later precipitation. It should be noted 

 that the proportion of heat (and 

 therefore water) lost through evapo- 

 ration would be greater if cooling 

 towers were used. 



Needed Research 



We need to be able to predict the 

 local thermal effects with more pre- 

 cision and, in particular, to study the 

 way in which the hot plume disperses, 

 paying particular attention to rates 

 of diffusion. In Lake Michigan this 



should be much more than an engi- 

 neering study through physical or 

 numerical models. It should also in- 

 clude an in-lake hydrographic study, 

 because the current regime and conse- 

 quent diffusion in the lake itself 

 varies greatly. And we need to ex- 

 amine not only the average long- 

 term circulation patterns, but also the 

 fluctuating circulation patterns asso- 

 ciated with such temporary phenom- 

 ena as upwelling, internal waves, and 

 thermal bars. There are a number of 

 mechanisms that sometimes tend to 

 keep water near shore for days or 

 weeks. This is not to say that the 

 lake is not well mixed at other times; 

 indeed, at least once a year, in Janu- 

 ary, it is probably very thoroughly 

 stirred. But we must also consider 

 the consequences of rare types of cir- 

 culation with minimal diffusion — for 

 example, under extreme thermal-bar 

 conditions — which may develop per- 

 haps once every ten years. 



And then, of course, there are pos- 

 sible biological effects. We clearly 

 need surveys to identify biologically 

 sensitive areas. We could learn much 

 by carrying out some of these surveys 

 near existing large fossil-fueled sta- 

 tions. These have been operating for 

 years, but no one seems to have re- 

 ported major deleterious effects on 

 Lake Michigan. We should certainly 

 look and see if there are any; we 

 should also try to differentiate be- 

 tween true thermal effects and those 

 arising from material wastes, looking 

 also for interactions, harmful or bene- 

 ficial, between thermal discharges and 

 more conventional pollution. 



At the same time, there should be a 

 thorough search of the literature. 

 There is a large body of published 

 material, including that from Atomic 

 Energy Commission (AEC) labora- 

 tories or AEC-supported work, on 

 the effect of radioactive materials and 

 thermal discharges on organisms. 

 The public is clearly thirsting for 

 knowledge on this subject, and anno- 

 tated bibliographies would be most 

 useful. We hear a great deal of loose 

 talk about the harmful effects of 



radioactive and thern; urges, 



so we should at least know what has 

 been done before we decide which 

 research gaps need filling. 



Special studies should be made in 

 the biological field. These should be 

 concerned with concentration effects, 

 already mentioned, and with the in- 

 fluences to which aquatic organisms 

 are subjected in a fluid in which, 

 while the levels of radioactivity may 

 be very low, they spend the whole 

 of their lives. 



Engineers and others should be 

 encouraged to collaborate in pilot 

 studies leading to the beneficial use 

 of waste beat. A number of ex- 

 ploratory projects are already under 

 way: irrigation of fruit orchards to 

 avoid frost damage; fish culture; 

 raising the efficiency of other waste- 

 disposal systems. 



Finally, we come to planning and 

 to the value judgments that planning 

 entails. There is a great need for 

 over-all regional planning, for ex- 

 ample to decide on the siting of new 

 nuclear power stations. They must 

 avoid biologically sensitive areas 

 (e.g., fish breeding grounds), they 

 should not be grouped to aggravate 

 the thermal effects, and if possible 

 they should be placed where they 

 could be useful. If, for example, 

 waste heat could be used to keep the 

 St. Lawrence Seaway open for a few 

 more weeks in winter, that would 

 permit overseas shipping lines to 

 make one more run per year to the 

 Great Lakes — a tangible benefit. 



With competent and imaginative 

 research and planning and with in- 

 telligent siting of power stations, it 

 should be possible to enjoy the bene- 

 fits of nuclear power without threat 

 to other users or to our enjoyment 

 of the Great Lakes. The research 

 should include not only the study 

 of near shore water circulation and 

 the ecological consequences of the 

 temperature rise, but also advanced 

 engineering leading to beneficial uses 

 of the waste heat. Design and plan- 



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