hurricanes. Under certain circumstances, the major shoreline 

 evolution is likely the result o£ infrequent but disastrous 

 events such as hurricanes. 



(3) All available survey data (profiles) and aerial photos 

 of the shoreline to help understand the existing problems, or to 

 anticipate the problems in construction of a proposed structure 

 or topographic modification. 



(4) Accurate simultaneous measurements of the wave environ- 

 ment and sediment transport (both onshore-offshore and along- 

 shore) . These measurements are the integral parts of the data 

 necessary for model verification. Measurements of the accuracy 

 and extent desirable for model verification have never been 

 obtained; however, it is realistic to obtain such data. The 

 length of time of the measurements must extend over an erosion 

 and accretion period and hopefully over a period of both high 

 and low littoral transport. Thus, the longshore transport com- 

 putation described is also used to select the optimum time of 

 year for the prototype data acquisition effort to have the de- 

 sired erosion and accretion periods occur within the shortest 

 possible time interval. A reasonable estimate of the time re- 

 quired for acquisition of the desired data is 1 to 3 months. 

 The wave measurements must be accurate and must include the 

 directional spectrum. Although both the planning and analysis 

 are difficult, it is definitely within present capabilities. 

 One reason that past attempts at measuring the directional spec- 

 trum have been of limited success is the lack of sufficient re- 

 dundancy in the number of wave sensors to validate the statistics 

 and to prevent the results from becoming questionable when one or 

 two sensors develop problems. These measurements should be made 

 just outside the breaking zone for the largest waves anticipated. 

 A system similar, or one identical to that used by the U.S. Army 

 Engineer Waterways Experiment Station (WES) in the Los Angeles- 

 Long Beach Harbors study (Pickett, Durham, and McAnally, 1975) 



is recommended. The WES system consisted of pressure transducers 

 with ranges of 25 and 50 pounds per square inch, and with a very 

 accurate response. A minimum of problems occurred during a year's 

 use, and all data were recorded in digital form on magnetic tape. 

 One tape contained approximately 5 days of data for 15 sensors 

 at a sample rate of one sample per second. The sample rate was 

 flexible and could either be increased or decreased as the sit- 

 uation required. Careful planning of the sensor spacing is 

 required to ensure both the desired accuracy and resolution; 

 measurement of atmospheric pressure is also required. All data 

 should be analyzed during periods of rapid erosion, accretion, 

 and littoral transport. Segments of data should be analyzed at 

 least every 6 hours during the entire test program. These data 

 would be used for input to the wave generator during model veri- 

 fication. In addition to the wave sensor data, photos should be 

 taJ<en periodically each day to show the wave breaking angle and 



290 



