Tide Measurements Water levels are measured constantly at numerous tide stations along Canada's mainland coast and on the major sea islands. A tide gauge must be in place for at least 19 years to record all the possible ranges of tides, because that is the cycle of the relative motions of the earth, moon and sun. Since the dawn of history the rise and fall of tides have been studied by people near the oceans. Not surprisingly, therefore, the terminology of tides has become a part of our everyday language. Spring and neap tides have already been defined.
Flood tide is the incoming or rising water, and ebb tide is the reverse.
The tide turns when the water has reached its maximum and starts to fall or has reached its minimum and starts to rise. On old nautical charts the terms spring and neap were commonly used to describe the tidal range of a port or anchorage. Although these terms are firmly embedded in nautical lore they are not used in modern tide tables or on modern charts. Modern terms are more precise than the older terms in describing tidal surfaces which, in the real world, are affected by both astronomic attraction and local effects of water flow and weather. Even lower tides may occur rarely if strong or persistent winds and storm surges work to further lower the water.