Tide Gage

an instrument for measurement and continuous automatic recording of fluctuations in the level of the sea. Tide gages are made for use on shore and on the open sea.

The most common shore tide gage, used at permanent observation points, is the float-type sea-level recorder. Its principle of operation is based on conversion of vertical displacements of a float into proportional displacements of a pen, which records them on a graph tape mounted on a drum, which is rotated by clockwork. A recording scale of 1:10, 1:20, or 1:40 may be used, depending on the magnitude of fluctuations in sea level at a particular point.

The float of a tide gage is mounted in a well, which communicates with the sea through a pipe or a hole in the wall. The well eliminates waves caused by the wind and protects the float from outside influences. For transmission of readings over distances (by wire or radio), auxiliary devices are used that convert the vertical displacements of the float into electrical impulses.

In the coastal zone of seas, tide gages whose principle of operation is based on measurement of the hydrostatic pressure of a column of water are also used. The level sensor is set on the bottom or secured to an underwater part of a hydraulic engineering structure. Self-contained hydrostatic tide gages (GM-28) are used to study fluctuations in the water level at temporary points; in such gages the sensor and recorder are mounted in a single container. In another type of hydrostatic tide gage, the recording part is mounted on land and changes in pressure are transmitted to the recorder through a pipe. In these instruments the level is transmitted by radio, in addition to being recorded on tape.

Open-sea tide gages are also based on the principle of recording changes in hydrostatic pressure. They may be set on the bottom (when the depth does not exceed 200-250 m) and will record automatically for up to a month.