to 60° Fahrenheit. As low-pressure systems passed through the area, 

 the daily temperature range was reduced from an average range of 20° to 

 25° to 10° to 15°. With the passage of a low (e.g., 6 and 14 July) out 

 of the area, the air temperature range increased, usually within 1 day. 

 However, water temperature required 2 to 4 days to return to previous 

 conditions. From the middle of July until the end of the study period, 

 the mean water temperature increased as the surface waters were gradu- 

 ally heated by higher summer temperatures. 



3. Wave Measurements . 



The relationships between barometric pressure, breaker height, and 

 breaker power are shown in Figure 6. With the passage of low-pressure 

 systems over Plum Island (6 and 14 July), breaker height and breaker 

 power tended to increase. The increase in breaker height on 15 July was 

 due to long-period swells generated by a low-pressure system which passed 

 through the area on 14 July. The effect of changes in breaker power is 

 discussed later. 



Wave steepness data and breaker height measurements are given in 

 Figure 7. A comparison of wave period and barometric pressure for the 

 summer period reveals no consistent correlation between local pressure 

 systems and wave period. Local shifts in wind direction may cause short- 

 period waves to form and coexist with longer period waves generated far- 

 ther offshore. Late afternoon southeasterly winds were usually responsi- 

 ble for these short, 5- to 6-second waves, but as the wind velocity 

 decreased after several hours, only longer period waves persisted. 



The daily fluctuations in breaker height and wave steepness were due 

 to surging-type waves occurring at high tide. The surging waves averaged 

 less than 30 centimeters in height and were less steep than spilling and 

 plunging waves. 



Breaker- angle measurements are affected by changes in wind conditions 

 more rapidly than most other wave parameters. The relationships between 

 alongshore wind components, those components which are locally responsible 

 for the direction of wave approach, and breaker angle are presented in 

 Figure 8. The lack of northerly or northeasterly winds resulted in few 

 positive alongshore wind components and hence few positive breaker angles. 

 Increases in the magnitude of alongshore wind components often result in 

 a corresponding increase in breaker angle. However, high breaker-angle 

 measurements were never accompanied by high-energy wave conditions suffi- 

 cient to cause marked beach erosion. 



4. Ground Water Measurements. 



Hourly ground water readings revealed close relationships between 

 ground water elevation above MLW and tides, precipitation, and breaker 

 height (Fig. 9). Ground water elevations before 10 July were not recorded 

 because of instrument problems. Changes in ground water elevation lag 

 approximately 3 hours behind changes in the tide. The effect of spring 

 and neap tides for parts of the ground water elevation curve is shown in 



24 



