A MULTI-PURPOSE DATA ACQUISITION SYSTEM FOR INSTRUMENTATION 

 OF THE NEARSHORE ENVIRONMENT 



by 



W. A. Koontz and D. L. Inman 



Section I. INTRODUCTION 



Most energy from ocean waves and tides is ultimately transmitted to 

 the ocean periphery. Within the ocean periphery or nearshore zone, the 

 energy is dissipated in various ways including reflection, generation of 

 turbulence and longshore currents, transportation of sediment, and the 

 formation of other kinds of waves. Some energy appears to become "trapped" 

 against the coast in the form of edge waves and shelf seiche, thus leading 

 to an increase in the energy level at the coast. 



The many forms of energy flux and the high rates of energy dissipation 

 near the surf zone cause the nearshore environment to be complex and one 

 of intense interaction among waves, currents, and sediments. Understanding 

 the processes in the nearshore environment requires a careful assessment of 

 the amounts of energy in the various kinds of wave motion; determination of 

 the mechanics of interaction of waves, currents, and sediments, as well as 

 the careful evaluation of the rates of energy transfer into the formation of 

 turbulence and heat and into the longshore transport of water and sediment. 

 It seems likely that assessment of the energy in the various modes of wave 

 motion can only be accomplished by instantaneous-synoptic measurements in 

 and near the surf zone from a grid or array of sensors. In the simplest 

 form the sensors would all be of the same kind (e.g., pressure, water level, 

 etc.). The array should have both on-offshore and longshore components, 

 with spacings between sensors that are of the order of one-quarter wave 

 length. An array is necessary because measurements at one or two points 

 cannot give direction of energy transport, nor distinguish between phe- 

 nomena having similar frequencies but different modes (i.e., swell vs. 

 edge waves; standing vs. progressive waves). Understanding the mechanics 

 of interaction and transport also requires instantaneous-synoptic measure- 

 ments from a number of sensors. However, in this case, the sensors are 

 likely to be of different kinds and their array of smaller dimensions, 

 say, the thickness of a boundary layer or the orbital diameter of a water 

 particle trajectory. A typical investigation might include the simultaneous 

 measurements of water velocity at several elevations, suspended sediment 

 concentration at several points, and the water level and pressure field 

 of the traveling wave. 



It is interesting to note that laboratory and model studies of near- 

 shore phenomena require the same kinds and numbers of instantaneous-synoptic 

 measurements as the field studies, differing only in the scale of the sensor 

 array and the period of the sampling interval. 



