Figure 9 is an example of the Natural Bridges data obtained between April 1968 

 and December 1968. The table shows that 38 of 480 observations had wave heights 

 in the. interval 2.0 < H^ < 2.9 (since wave heights are only reported to the 

 nearest 0.1 foot this interval is effectively 2 < H b < 3.0) and with periods, T, 

 in the interval 13.0 < T < 13.9 (effectively 13 < T < 14.0). Conditional proba- 

 bilities can be developed from information in the table. The marginal proba- 

 bility data for wave periods are given in the last three columns of the table, 

 while marginal probability data for wave heights are given in the bottom three 

 rows. To a certain extent, the marginal probability data are redundant with 

 the probability data given in the histograms of Figures 7 and 8. 



4. Monthly Average Breaker Height and Period Versus Time . 



The time variations of the monthly average breaker height and period are 

 plotted against time in Figure 10 and seasonal variations of the parameters are 

 evident. The figure shows that average monthly wave heights dipped below 2 

 feet (0.6 meter) during the spring and increased to near 3 feet (0.9 meter) 

 during autumn in 1970. 



5. Longshore Currents Histogram . 



The longshore current histogram provides information on the frequency of 

 occurrence of current speeds and direction within specific speed intervals. 

 The current speed is tabulated in increments of 0.25 foot (0.08 meter) per 

 second. For example, tabulation in Figure 11 shows no current (calm) condi- 

 tions prevailed 29.9 percent of the time. For an observer facing seaward, cur- 

 rents moving to the right at speeds between 0.5 and 0.75 foot (0.1 and 0.2 

 meters) per second occurred 2.1 percent of the time. Currents moving to the 

 left at the same speed interval prevailed 2.1 percent of the time. 



6. Longshore Current Versus Time . 



Figure 12 is an example of the time history of longshore current velocity 

 at Natural Bridges for 1969. Each current observation is represented by a 

 vertical line above or below the horizontal line for currents to the right or 

 left, respectively. The length of the line corresponds with the magnitude of 

 the velocity. The monthly average current velocities are represented by cir- 

 cles. The figure shows that the average January current velocity was about 

 0.25 foot per second to the left, and the maximum observed current velocity in 

 January was about 1.0 foot per second to the left. 



VI. DATA PRESENTATION 



The data from the 25 northern California sites are presented in Appendix B 

 in geographic order, starting with the northernmost site at Pelican Beach State 

 Park to the southernmost site at Sunset Beach in Monterey Bay. All the data 

 for a given site are together. Yearly summary reports are given for each year 

 during which some data were collected, even if data were obtained for only a 

 few observations or a few months during that year. These annual summaries are 

 followed by a cumulative annual summary, in the same format, of all data from 

 the site. The period of record covered by each summary is given in the upper 

 right-hand corner of the sheet. 



21 



