the sand bottom is in flux except under the most calm conditions. Even 

 at the 6.1-meter depth sand is being transported regularly because of 

 wave energy (Fig. 7). This implies that the nearshore environment of 

 Imperial Beach was an area where sediment fluxes existed continually for 

 most of the year extending beyond the 3.7-meter depth. 



Table 6. Calculated horizontal velocity of wave motion (meters 

 per second) at the bottom for three wave energies, 

 three depths, and for three wave periods. 



Depth (m) 



Wave Energy^ 



Wave period (s) 



6 



1 12 1 



18 



3.7 



200 



0.28 



0.32 



0.33 



3.7 



400 



0.40 



0.45 



0.46 



3.7 



600 



0.49 



0.55 



0.57 



6.1 



200 



0.20 



0.24 



0.25 



6.1 



400 



0.27 



0.34 



0.35 



6.1 



600 



0.34 



0.42 



0.43 



12.2 



200 



0.10 



0.16 



0.17 



12.2 



400 



0.14 



0.23 



0.24 



12.2 



600 



0.17 



0.28 



0.30 



•'■Wave energy per unit surface area per square centimeter, 

 E = pg<n^>, where p = fluid 

 acceleration (see Sec. Ill) 



V. BIOLOGICAL RESULTS 



1. Sampling Design Effectiveness . 



If sampling data and conclusions derived from monitoring, re- 

 search and survey programs are to be utilized in decisionmaking 

 processes, it is necessary to know the levels of precision and con- 

 fidence of statements made regarding such community attributes as 

 abundance and diversity. These considerations are essentially a 

 function of error in taking samples and inherent variability of sampled 

 properties. Since most biological data are typified by high variance, 

 this study hoped to minimize the variance and increase precision by 

 extensive replication with small sampling units (Elliott, 1971) and 

 reduce bias in sampling by using hand-operated core samplers which 

 minimize sediment disturbance and take a consistent sample volume. 



47 



