force responsible for sediment entrainment, transport, and deposition, 

 whether occurring in open shelves or in entrances to harbors and tidal 

 inlets. Recent evidence suggests that sediment transport is not limited 

 to the narrow zone between the breaking waves and the limit of their up- 

 rush, but that currents of various origin actively transport sediments 

 parallel to shore as distantly as the edge of the Continental Shelf. 

 This sediment transport has implications in offshore engineering, an area 

 of increasing concern. 



In nearshore areas, the main contributing factor to current generation 

 is the waves shoaling over the Continental Shelf and refracting with de- 

 creasing depth. Depending on the angle of incidence between the wave 

 orthogonal and the bottom contours (ultimately the shoreline) , coastal 

 currents might be generated parallel or normal to shore, a matter of 

 considerable engineering significance. The currents contain an admixture 

 of periodic and aperiodic water motions. However, in several geographic 

 areas superimposed wave trains of different amplitudes, frequencies, and 

 directions will combine to produce random wave fields. The flow generated 

 by these waves may be stochastic or ergodic (or neither) . During the 

 passage of storms, the wave field and the resulting flow field may also 

 become nonstationary. 



The laminar nature of the flow to this point was implicitly assumed, 

 and for the potential flow region of relatively deep waters, this assump- 

 tion may often be correct. However, at the sea floor the boundary layer 

 may be intermittently to fully turbulent independently of the nature of 

 flow above it. As the water depth decreases shoreward the scales of 

 motion become compressed from three into two dimensions and the result is 

 that coastal, shallow-water currents become increasingly more turbulent 

 for the full depths of flow. This action induces mixing which is charac- 

 teristically at maximum near breaking waves and by its rotational nature 

 drastically modifies the current -induced motion of sediments. Other 

 effects, such as wave-wave interaction and wave-current interactions, 

 also influence forces imparted to the flow and the sediments. When ex- 

 periments are designed for the measurement of currents, essentially two 

 techniques are available: the Eulerian method and the Lagrangian method. 

 With the Eulerian method, water motion is observed past one or more fixed 

 points; with the Lagrangian method, a water particle is followed down- 

 stream, and changes in its motion (speed and direction) are observed. 

 Neumann (1968) stated, "The most complete description of oceanic currents 

 is obtained from a combination of both Eulerian and Lagrangian methods." 

 This statement is equally appropriate to shallow-water currents whose 

 variations in space and time near the coast, are even more complex than 

 those of major ocean currents. 



This study describes Eulerian and Lagrangian techniques used in the 

 measurement of coastal currents. Through technological improvements for 

 the survey of the nearshore flow characteristics, new experimental ration- 

 ale were developed. The report also documents data collection methods and 

 discusses problems attendant to obtaining accurate measurements. 



