Tide Observations at Baltimore and the Problem of Coastal Stability

T I lHE principal features that characterize the rise and fall of the tide at any place can be determined with sufficient precision for most purposes from observations covering a period of a year, and for general nautical purposes even a month or two may be enough. Consequently, although the tide tables issued annually by each of the principal maritime nations as essential aids to navigation carry tidal data for several thousand places throughout the world, it must be borne in mind that these data are derived very largely from short series of observations. And although such data may be adequate for the purpose of the tide tables, it must not be assumed that the observations on which they are based are adequate for answering several interesting questions which systematic tide observations can answer. Indeed, even where tide observations have been taken continuously for many years, it does not necessarily follow that they are systematic. Briefly, systematic tide observations may be defined as observations covering a number of years during which the heights were referred to a tide staff whose elevation was checked periodically with adequate bench marks on the shore. It may be said that, in general, there are relatively few series of systematic tide observations that cover many years. It is for this reason that the series of tide observations begun at Baltimore in I902 is of especial interest. During all this time the tide staff has been tied in periodically with a number of bench marks on shore. It happens, too, that since the very beginning, the observations have been made by the same tide observer. At the end of I942, therefore, there was available at this station a series of systematic observations covering forty years. These observations constitute the longest series of continuous systematic tide observations taken on the Atlantic coast of the United States. Of their manifold interest, we shall here limit ourselves to a single aspect, namely the light these observations throw on the problem of the vertical stability ot the Atlantic coast. The data that bear directly on this problem are those referring to the height of sea level. But it will be of advantage to consider briefly the question whether there has been any change in the tidal regime at Baltimore, since it might be urged that changes in tidal regime may cause changes in