Tides, types of:
The characteristic form of the tide with special reference to the relation of the DIURNAL and semidiurnal waves. Tides are sometimes classified as DIURNAL, SEMIDIURNAL and MIXED, but there are no sharply defined limits separating the groups. The tide is said to be DIURNAL when the diurnal wave predominated and only a single high and single LOW WATER occur each day during the greater part of the month. The tide is SEMIDIURNAL when the semidiurnal wave predominates and two high and two low waters occur each tidal day with a relatively small inequality in the high and LOW WATER heights. In the MIXED type of tide the DIURNAL and semidiurnal waves are both important factors and the tide is characterized by large inequality in the high or LOW WATER heights or in both. There will usually be two high and two low waters each day, but occasionally the tide will become DIURNAL.
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