MEASUREMENT TECHNIQUES FOR COASTAL WAVES AND CURRENTS 



by 

 P.G. Teleki, F.R. Musialoioski , and D.A. Prins 



I . INTRODUCTION 



1. General Concepts , 



The coastal zone is the most frequently observed part of the ocean. 

 Its shorelines have been explored and described for at least two cen- 

 turies, but only in the last 20 years have coastal resources been studied 

 or damages to property systematically documented; however, considerable 

 knowledge about some of its most important physical processes remains to 

 be secured. 



This report examines a manner in which coastal currents, one of the 

 least understood processes, may be studied. Currents represent the flow 

 of water which transport and disseminate heat, salt, and particulate 

 matter. Currents converge near headlands and marine structures, diverge 

 near islands and in bays, and influence navigation. Because they are 

 the main transportive mechanism for the sediments on the ocean floor, 

 currents in coastal areas often interfere with human intentions by erod- 

 ing and depositing sand in undesired locations and in undesired quantities, 

 Probably half of all problems in coastal engineering can directly be 

 traced to this physical process. 



The study of currents requires recognition that the flow of water in 

 relatively shallow water may originate in one or more of the following: 

 Wind, waves, tides, density stratification, and even internal waves. The 

 most difficult part of analyzing current records is perhaps in assigning 

 the proper weight to each of the components in a field of complex or 

 interactive flow; also difficult is the assessment of temporal and spa- 

 tial variabilities (or stabilities) or the modeling of the currents for 

 predictive purposes. 



Coastal currents characteristically exhibit the effect of seasonal 

 changes and trends which may be peculiar to a geographic area of study, 

 and incorporate components of the large-scale circulation of the oceans. 

 Experiments which include consideration of long-term changes in current 

 velocities, distribution, and structure are not commonly planned for the 

 coastal zone. 



Engineering practice often classifies coastal currents by direction 

 (onshore versus alongshore) and by area shoreward or seaward of the zone 

 of breaking waves. Coastal engineers prefer to emphasize the longshore 

 currents generated by breaking waves, a natural consequence of its rela- 

 tion to littoral drift; oceanographers tend to view coastal currents in 

 a slowly varying, wind- and pressure-driven, stratified, and bathymetry- 

 dependent sense. In either case, currents represent a sediment-moving 



