Accession Number : AD0661626

Title :   FREQUENCY RESPONSE OF TIDE GAGES.

Descriptive Note : Technical rept.,

Corporate Author : CALIFORNIA UNIV BERKELEY HYDRAULIC ENGINEERING LAB

Personal Author(s) : Cross,Ralph H.

Report Date : AUG 1967

Pagination or Media Count : 16

Abstract : The most common source of data on tsunamis is from the records from permanently installed tide gages. A tide gage commonly consists of a float in a stilling well. The float is connected to a mechanical recorder, and the stilling well serves to eliminate the effects of wind waves and swell from the gage response. This damping of the higher-frequency wind waves is achieved by an orifice connecting the float chamber of the stilling well to the sea. This orifice acts as a filter, damping out the higher wind-wave frequencies, while allowing the much lower tidal frequencies to pass without loss in amplitude. Tsunamis, however, fall between the wind-waves and the tides in the frequency spectrum, and thus it is important to know the response of a tide gage at 'typical' tsunami frequencies. These results show that for most ordinary purposes, the tide gage stilling wells described -- i.e., a 12-in. diameter well, with either a 3/4-in. or 1-in. diameter orifice, give a good representation of a tsunami, if the periods are larger than 5 min. for tsunamis 2 ft. high, or 15 min. for tsunamis 20 ft. high. The graphs provide a means for estimating both the reduction in height and the time lag of the peak. (Author)

Descriptors :   (*TIDES, MEASURING INSTRUMENTS), OCEAN WAVES, FREQUENCY, RESPONSE, PIPES, WIND, MECHANICAL WAVES, HYDROSTATIC PRESSURE, MATHEMATICAL ANALYSIS, ORIFICES

Subject Categories : Physical and Dynamic Oceanography
      Test Facilities, Equipment and Methods

Distribution Statement : APPROVED FOR PUBLIC RELEASE