91. Mean and extreme monthly tide levels (Figure 27) show a 5- to 

 6-month periodicity; this phenomenon is due in part to the inclination of the 

 Sun, a long-period astronomical tide constituent which has a periodicity of 

 approximately 6 months. Additionally, astronomical forces with annual period- 

 icity and the seasonal oscillation of the specific volume of sea water as a 

 function of temperature, called the Steric effect, may explain the observed 

 periodicity in the data (Pattullo et al. 1955). Strong offshore winds dur- 

 ing most of April 1981 may in part explain its anomolously low water level 

 statistics . 



92. Although the annual statistics were nearly the same, hourly, daily 

 high, and daily low tide height distributions for 1981 versus 1980 (Figure 28) 

 reveal that during 1981 the high tides which occur infrequently--e.g. , less 

 than 2 percent of the time--were higher than those of the previous year. 

 These extreme water levels were associated with meteorological events which 

 coincided with spring tides. For comparison, during 1979 and 1980, 1 percent 

 of the hourly tide heights exceeded 80 cm, while in 1981, 1 percent exceeded 

 90 cm. On four occasions during 1981, the water level exceeded the highest 

 water level previously recorded since 1979. The numerous extreme water levels 

 during the year, with the associated wave conditions and coincident tidal 

 stages, are tabulated below: 



Comments 





Ext: 



reme High 







Date 



Water 



Level, 



, cm 



Wave 



Height, m 



4 May 





115 







2.7 



30 Jun 





126 







1.8 



20 Aug 





140 







3.1 



13 Oct 





125 







2.6 



13 Nov 





149 







3.5 



Monthly spring tide 



Monthly spring tide 



Tropical Storm Dennis 



Perigean spring tide 



Perigean spring tide coincident 

 with severe northeaster storm 



11 Dec 113 1.0 Proxigean* spring tide 



* Explained below. 



93. Wood (1978) discusses perigee-syzygy and the occurrence of coastal 

 flooding (when coincident with strong and persistent onshore winds) associated 

 with the reduced lunar distances and solar-lunar alignment during perigean 

 spring tides. Wood attributes the high water levels to the reinforcing effect 

 that the alignment of the Sun's and Moon's gravitational forces have on the 



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