V. CONCLUSIONS AND RECOMMENDATIONS 



Techniques related to the measurement of flow in the nearshore zone 

 have been surveyed, and the advantages and disadvantages associated with 

 the various approaches discussed. The advantages are: (a) The ability 

 to negotiate the surf zone with instruments mounted on the sea sled; 



(b) a near-continuous mode of operation for measuring waves and currents 

 contemporaneously and chart their distribution in the spatial sense; 



(c) to see the data in real time for maximizing the conditions in collect- 

 ing useful information; and (d) the ability to combine Eulerian and 

 Lagrangian techniques for the complete description of flow. 



The disadvantages are: (a) The present inability to obtain Lagrangian 

 correlation scales independent of dye studies by measuring currents si- 

 multaneously with sets of meters at two locations; this requires another 

 sea sled and corresponding instrumentation for the two platforms to be 

 deployed at the upstream and downstream boundaries of the test area where 

 diffusion studies are conducted; (b) the time needed to adjust the spars 

 so that data points in space would be dispersed equidistant ly from one 

 another and from the reference water surface, thus providing a means to 

 record wave attenuation along a shore-normal profile using a constant 

 pressure correction factor; and (c) the present method of measuring cur- 

 rents near the bottom boundary. The location of the instrument and power- 

 packs restricts mounting of sensors to elevations 0.91 meter above the 

 bottom, when placements closer to the ocean floor may penetrate the 

 boundary layer of slowly varying shelf currents. 



The sea sled is an ideal vehicle for the measurement of currents and 

 waves (as presently done), or salinity, temperature, and sediment content. 

 Water temperatures were read during one of the experiments, including wind- 

 speed and direction necessary to estimate the influence .of wind stress on 

 the time required to set a lake into motion or on the dispersal of a dye 

 plume. 



The dye experiments are an integral part of a nearshore current study, 

 because mixing (turbulent diffusion) is nonnegligible near the coast and 

 the records obtained from in situ sensors contain information on the tur- 

 bulent part of the spectrum. The development of a dye plume is followed 

 by aerial cameras which record the zones of intense mixing, allow the 

 experiments to assess the aerial variations in current speed at the surface 

 near the fixed-point sensors, and thus gain insight of upstream histories 

 for the iKoastal flow. Repetitive photo coverage is useful in estimating 

 horizontal and lateral diffusion coefficients when the proper injection 

 algorithm is applied and the dye concentrations are measured in the field. 



The ultimate use of such information is for sediment transport calcu- 

 lations in coastal areas and for the evaluation of the performance of 

 engineering structures. Necessarily, these are often interrelated. How- 

 ever, a sufficiently wide range of environmental conditions may be tested 

 in time, the evaluation of which would result in producing predictive 

 models and design curves useful to the coastal engineer. This study has 

 documented these needs and expectations, provided an insight into the prob- 

 lems, and recorded some of the accomplishments. 



68 



