Why is it important to use a particular tidal epoch?
Tidal records typically contain secular trends in addition to the periodic variations. Over time, the secular trend can alter the relative elevation between tidal and related terrestrial datums. When comparing elevations which are based upon tidal datums, one should insure that common epochs are used in order to account for the effects of secular trends. Moreover, the presence of a secular trend can cause changes in related tidal datums, such as MLLW and MHHW. Back to top 8. How are geodetic and tidal datums related? Back to top 9. How are the differences between terrestrial and tidal datums linked? Back to top 10. How great a distance from a tide station can I move and still have a valid tidal/terrestrial datum relation? In the strict sense, a tidal datum is applicable only at the location of the tide station. This is because tides and therefore tidal datums are affected by the gradient of the geoid. In order to validly extend a tidal datum over some horizontal distance, the geoid gra
