Also of considerable significance in consideration of the role of 

 onshore and offshore winds is their interlock with water density, Xll. If 

 the wind hlows offshore long enough and strong enough, the wind stress at 

 the water surface produces a seaward movement of the upper layers of the 

 ocean and a shoreward return flow in the lower layers. (The procedure is 

 more or less reversed with an onshore wind. ) This sort of "pseudo-upwell- 

 ing" results in the shoreward movement of colder, more-saline water in the 

 summer months and relatively warmer, more-saline water in the winter months. 

 This type of turnover of the continental- shelf waters has been undergoing 

 documentation by the Virginia Institute of Marine Science for over two 

 years, using sea-bed drifters and sea-surface drift bottles. In addition, 

 the temperature and salinity measurements made at the 15th Street pier 

 correlate well with observed offshore and onshore wind movements. Thus, 

 there is a clear interlock between Uq-^, Uqjj, aad Pi And water density 

 will clearly influence fluid drag velocities and turb-ulence at the bed and, 

 thereby, the particle-size distribution in the shoaling-wave zone. 



Summary;. — Based upon an analysis involving 12 independent variables, 

 average mean size on the shoaling-zone slope at 15th Street, 250 feet 

 beyond the breakers, is most-influenced by the combination of variables 

 (taken arbi^crarily in a combination of six) composed of mean slope, wave 

 period, wave steepness, wind velocity parallel to shore, angle of wave 

 approach, and tidal-current velocity. This combination of variables is 

 most influential on {^1^)3 after a lag in time of 8-12 hours. 



Mean slope is the most-dominant independent variable at all times. 

 When removed from the analysis, it is in the main replaced by water density, 

 and this variable is found to be of considerable importance in all of the 

 strong combinations of variables. 



The importance of wind velocity onshore and S^fshore in the analyses 

 is found in their interlock with water density as it will change when shelf 

 water in the lower layers is moved to the shore during offshore winds and 

 out to sea under onshore winds. The shelf water in the upper and lower 

 layers is stratified as to density, especially during the summer months, 

 and the density affects the sizes of particles moved. 



Wind velocity parallel to shore is significant in its ability to 

 reinforce or decrease tidal-current velocities near the bottom, because 

 tidal currents in the study area flow generally parallel to shore. The 

 angle of wave approach is probably of significance as it interlocks with 

 tidal-current velocity. Wave-drift and tidal currents interlock in their 

 effect on particle movement at the bed. 



FUTURE STUDY 



A major aim of any search for significant interactions in a natural 

 system is to provide a basis upon which more formal models may be erected. 

 The authors are continuing their efforts in this direction, using the pre- 

 sent data set. Additional techniques (for example, factor analysis and 

 discriminant functions) will be examined. The data set will also be 



