Theoretical and applied research dealing with tsunami problems has 

 been greatly intensified since 1960. Preisendorfer (1971) lists more than 

 60 significant theoretical papers published since 1960. The list does not 

 include observational papers concerned with the warning system. 



3.83 LAKE LEVELS 



Lakes have insignificant tidal variations, but are subject to sea- 

 sonal and annual hydrologic changes in water level and to water level 

 changes caused by wind setup, barometric pressure variations, and seiches. 

 Additionally some lakes are subject to occasional water level changes by 

 regulatory control works. 



Water surface elevations of the Great Lakes vary irregularly from 

 year to year. During each year, the water surfaces consistently fall to 

 their lowest stages during the winter and rise to their highest stages 

 during the summer. Nearly all precipitation in the watershed areas during 

 the winter is snow or rainfall transformed to ice. When the temperature 

 begins to rise there is substantial runoff - thus the higher stages in the 

 summer. Typical seasonal and yearly changes in water levels for Lake Erie 

 are shown in Figure 3-39. The maximum and minimum monthly mean stages for 

 the lakes are summarized in Table 3-6. 



Table 3-6. Fluctuations in Water Levels - Great Lakes System (1860 through 1973). 



Elevations are in feet above mean water level at Father Point, Quebec. 



International Great Lakes Datum (IGLD) (1955). 



* To convert to U.S. Lake Survey 1935 Datum, add datum factor to IGLD (USLS 1935 = IGLD + datum factor). 



t Low water datum is the zero plane on Lake Survey Charts to which charts are referred. Thus the zero (low water) 



datum on a USLS Lake Superior chart is 600 feet above mean waterlevel at Father Point, Quebec. 

 If Lake St. Clair elevations are available only for 1898 to date. 



In addition to seasonal and annual fluctuations, the Great Lakes are 

 subject to occasional seiches of irregular amount and duration. These 

 sometimes result from a resonant coupling which arises when the propaga- 

 tion speed of an atmospheric disturbance is nearly equal to the speed of 

 free waves on a lake. (Ewing, Press and Donn, 1954), (Harris, 1957), 

 Platzman, 1958, 1965.) The lakes, also and sometimes simultaneously, are 

 affected by wind stresses which raise the water level at one end and lower 

 it at the other. These mechanisms may produce changes in water elevation 

 ranging from a few inches to more than 6 feet. Lake Erie, shallowest of 



3-76 



