98. Daily water visibility values, measured at the seaward end of the 

 pier are shown in Figure 32. In 1981, as in 1980, largest day-to-day visibil- 

 ity differences occurred during the suouner months, since the pattern of off- 

 shore and onshore winds that produced major temperature differences also con- 

 trolled the visibility. The warm surface water is usually quite clear, while 

 the cooler bottom water contains large concentrations of suspended matter. 



99. Figure 33, the distribution of surface water visibility for 1981 

 and 1980, shows that the 1981 values were much lower than those for 1980. 

 1981 and 1980 data combined indicated that 50 percent of the time the visibil- 

 ity was greater than 1 m and that 10 percent of the time visibility exceeded 

 3.5 m. Table 9 gives a summary of the water visibility data. Monthly mean 

 visibility values for 1981 (Figure 34) and the seasonal distribution of visi- 

 bility for the combined 1980 and 1981 data (Figure 35) show the seasonal 

 variability typical at the FRF: higher values in the summer than during the 

 remainder of the year. 

 Surface water density 



100. Although there was considerable scatter in 1981 surface water 

 density values (Figure 36) , monthly mean values generally show an inverse 

 dependence on water temperature (Figures 37 and 30) . This pattern may be 

 affected by rainfall; however, large amounts of rain occurred in July and 

 August when density values were at a minimum (Figure 38 and Table 9). No 

 density data were collected during 1980. 



Survey Data 



101. Waves and currents interacting with the beach and nearshore cause 

 increases and decreases in the amount of sediment as a result of longshore 

 transport, movement of the bar(s) on- or offshore, and the exchange of sediment 

 between the beach and nearshore bottom. These changes can occur very rapidly, 

 in response to a storm, or slowly as a result of seasonal variations in wave 

 and current conditions . 



102. In this section, time histories of bottom elevations at selected 

 locations along the pier and contour diagrams of the bathymetry from the dune 



to 1,000 m offshore for a 1,000-m distance along the beach (centered at the pier) 

 are presented. 



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