limitations in addition to other problems which deal only with 

 the generation of spectral waves; however, they are more diffi- 

 cult to define. 



(3) Remolding of bottom topography . After completion of 

 a test, one operational constraint is remolding of the bottom 

 topography. Since the topography may have changed, the entire 

 model area must be checked and remolded. During testing, segre- 

 gation by size frequently occurs if the model material is not 

 uniformly sized, necessitating remixing before remolding. 



c. Selection of Test Conditions . Selection of test conditions is a 

 relatively straightforward procedure. The first task is to obtain wave 

 hindcast data for the area of interest. Secondly, the littoral transport 

 rates should be computed for each segment of the wave climate. These 

 computations are not expected to be extremely accurate, but they should 

 yield an accurate picture of the relative importance of each part of the 

 wave climate concerning the transport of bed material. The above data, 

 along with those analyzed during the prototype data acquisition study, 

 should be adequate to allow an intelligent selection of test conditions. 

 The normal wave climate should be tested with particular emphasis on each 

 segment which produces a significant contribution to the yearly transport 

 rates in each direction. 



Depending on the prototype data acquired, it may be necessary to 

 either produce a wave spectrum in the model or to generate monochromatic 

 waves from more than one direction. 



d. Model Measurements . The primary model process of interest is 

 bottom evolution as a function of incident wave conditions, tide level, 

 and duration of wave conditions. Therefore, measurement of erosion and 

 accretion rates, bottom profiles, and longshore transport rates are de- 

 sirable. Accurate measurements of incident wave heights and tidal heights 

 (especially during model verification) are necessary. Model measurements 

 of wave heights and currents in shallow water and inside the surf zone 

 may also be necessary. 



Profiling of the model topography is extremely important and tedious 

 if not performed automatically. Several devices (acoustic and laser) are 

 well suited for this task. All data should be recorded on magnetic tape 

 for automatic data processing. 



Model measurements of onshore-offshore and littoral transport are 

 certainly as difficult as they are in the prototype. Either fluorescent 

 or radioactive tracers could be used satisfactorily in conjunction with 

 an automatic counter operating in much the same manner as the profiler. 

 If a device of this nature does not prove feasible, model sediment traps 

 may have to be devised. An excellent measure of the total longshore 

 transport rate can be ascertained from the amount of sand injected at 

 one boundary and then removed at the other boundary after equilibrium 

 conditions are established. 



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