TIDAL DATUM PLANES Se 
1925 1930 1935 1940 1945 
28 Los Angeles 
Sh) 
G6 | Seattle 
6.7 
ee 
8.0 Ketchikan * e 
Sal 
Fic. 54.—Yearly lower low water below yearly sea level. 
Definition of Mean Lower Low Water 
In view of the variations to which the height of lower low water is subject, mean 
lower low water at any place may be defined simply as the average height of the lower 
low waters at that place over a 19-year period. 
