the necessary model operating technique to reproduce the observed scour 

 and fill patterns. Thus, the accuracy and adequacy of prototype data 

 are very important. 



Verification of a movable-bed model is, theoretically, more difficult 

 than for a fixed-bed model. The purpose of a movable-bed model is to 

 simulate the evolution of the inlet bathymetry. This evolution takes 

 place in response to many factors, but primarily to the sediment washed 

 from adjacent beaches by wave action, to erosion of the inlet channel 

 by tidal currents, and to trapment of material at the bars on the ocean 

 and bay sides of the inlet. These same factors must be included in the 

 model to simulate degree as well as type of bathymetry evolution. 



Since a movable-bed model simulates shoaling and scouring patterns 

 in and near the inlet, the requirement that the model also simulate the 

 basic hydraulic quantities (tidal heights, tidal phases, velocities, 

 etc.) is somewhat relaxed. In practice, and contrary to the above dis- 

 cussion, the verification of a movable-bed model is a little easier than 

 for a fixed-bed model, since the experimenter has more variables available 

 with which to work to achieve the desired verification. 



The validity of tests of proposed improvement plans in a movable-bed 

 model is based on the following premise: If model reproduction of the 

 prototype force's known to affect movement and deposition of sediments 

 (tides, tidal currents, waves, etc.) produces changes in model bed con- 

 figuration similar to those observed in the prototype under similar con- 

 ditions, then the effects of a proposed improvement plan on the movement 

 and deposition of sediments will be substantially the same in both model 

 and prototype. 



Trends and magnitudes of prototype bed movement under existing condi- 

 tions are determined primarily through detailed comparison of two or more 

 periodic prototype surveys of the area under study. The time between the 

 earliest and latest surveys used in this comparison becomes the verifica- 

 tion period, and the movable-bed part of the model is molded to conform 

 to the prototype survey at the beginning of the verification period. The 

 model is then operated under conditions that existed in the prototype dur- 

 ing the verification period until model bed configurations throughout the 

 problem area are in conformance with those shown by the prototype survey 

 at the end of the period. Model bed movement is then considered to be 

 verified, or in proper adjustment, if changes in the model bed configura- 

 tions during the verification period agree reasonably well with those that 

 occurred in the prototype during the corresponding period. However, when 

 a model is operated in this fashion, basic similitude rules are ignored 

 and the model does not reproduce prototype forces. Only the sediment 

 motion at a particular point during a particular time period is being 

 modeled. Any major changes in hydrography may introduce errors into 

 the results. 



One very important reason for the verification of a movable-bed model 

 is the establishment of the time scale with respect to bed movement. The 



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