horizontal laminar flow and boundary conditions that include harmonic 

 oscillations of the ocean, sloping beaches of both ocean and pond, and a 

 horizontal lower boundary of the permeable sand bar. Laboratory models 

 (sandbox models) were used to test the reliability of the assumptions made in 

 the mathematical models. 



The tidal fluctuations of a pond near the north shore of the new volca- 

 nic island, Surtsey, off the south coast of Iceland, were measured in August, 

 1967. The pond amplitudes were about 0.56 of the ocean amplitudes and the 

 peak and trough delays were established to be 138 and 165 minutes respec- 

 tively. This asymmetrical response indicates that the mean pond level is 

 different from the mean sea- level. A mathematical flow model that gave good 

 agreement with the observed pond oscillations had a circular conical pond of 

 60 ms radius at mean sea- level and a 3 m depth with a 130 m wide circular sand 

 bar between the pond and the ocean. The required porosity of the sand was 

 about 0.4 and the effective permeability 2.5 cm/sec. The average depth to the 

 base of the permeable sand was set at 5 ms. These conditions required the 

 mean pond level to be 4 cm above mean sea- level. (Author). 



050 CHELTON JR., D. B. 1980. "Low Frequency Sea-Level Variability Along 

 the West Coast of North America," unpublished Ph.D Dissertation, University of 

 California, San Diego, CA, pp 212. 



The use of linear statistical estimators to examine dynamical models is 

 discussed and the importance of using multiple input statistical models rather 

 than a series of single input models is emphasized. A methodology is 

 described for determining the effects of statistical uncertainty in both time 

 and frequency domain multiple input statistical models. These methods are 

 then used to examine 30 years of nonseasonal tide gage and steric sea- level 

 data along the west coast of North America. The objective is to explore the 

 nature and causes of nearshore oceanic variability over short term climatic 

 time scales of months to years. 



After the tide gage records are corrected for the inverse barometric 

 effects of atmospheric pressure, it is found that there is close agreement 

 between the two measures of sea- level at frequencies less than 1 cycle/year. 

 At higher frequencies the steric sea- level variations measured relative to 

 500 db are on average, only about 1/2 as large as high frequency tide gage 

 sea-level variations. Higher frequency variations are primarily the result of 

 forcing by the local atmospheric pressure but the response is generally found 

 to be greater than inverse barometric (1 cm/mb) . Much of the remaining fre- 

 quency sea- level variability is the result of forcing by the wind field. The 

 longshore component of wind stress generally forces a larger sea- level re- 

 sponse than the onshore component but the important dynamical aspects of the 

 wind field generally appear to be basin wide rather than local. 



The dominant signal in residual sea-level after removing the atmospheric 

 and oceanographic effects as determined from the statistical models represents 

 long term trends over the 30 year record length. The trends at the lower 

 latitude stations are attributed to the eustatic rise . in sea-level from melt- 

 ing glaciers. The drop in measured sea-level at the higher latitudes has gen- 

 erally been attributed in the past to an apparent drop due to isostatic 

 rebound of the earth's crust from the most recent glaciation. However, it is 



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