TIDAL DATUM PLANES 109 
1946 | 1947 
Jan. Apr. July Oct. Jan. Apr. July Oct. Dec. 
Los Angeles 
Seattle 
Ketchikan 
Fic. 50.—Monthly lower low water, Los Angeles, Seattle, and Ketchikan, 1946-47. 
represented, the highest and lowest values of monthly lower low water differed by 0.9 
foot at Los Angeles, 1.5 feet at Seattle and 1.4 feet at Ketchikan. 
In the discussion of monthly sea level it was found that sea level at any place is 
subject to an annual variation which is characteristic for the region. In high water and 
in low water, likewise annual variations were found which closely resemble the annual 
variation in sea level at the place. It is therefore to be expected that lower low water 
should exhibit a similar annual variation. In Figure 51 are shown the monthly heights 
of lower low water at Los Angeles, Seattle and Ketchikan averaged from 19 years of 
observations, 1930-1948. 
