the movement of prototype bed material by the prototype hydraulic forces. 

 The coal used had a specific gravity of 1.4, a grain-size range of 0.1 

 to 5.0 millimeters, and a median grain diameter of 1.4 millimeters. Be- 

 yond the limits of the movable-bed section, the remainder of the model 

 bed was molded of concrete to provide space for the wave generator and 

 the inflow-outflow system required for the tide generator. 



The model was constructed to linear scale relations, model-to- 

 prototype, of 1:500 horizontally and 1:100 vertically. Other scale 

 relations such as time, velocity, discharge, and volume were computed 

 from these linear scales. The computed time scale of 1:50 was applied 

 only to reproduction of prototype hydraulic forces in the model and had 

 no relation to the time required for the model to reproduce observed 

 changes in prototype hydrographic conditions. The model layout is shown 

 in Figure 7-17. 



The following model operating procedure was developed during trial 

 verification tests: 



(a) The first cycle (about 30 minutes) was a normal tidal 

 cycle with waves . 



(b) Operation of the model tide generator was stopped when 

 ebb velocities reached a maximum, and the model was operated for 

 1 model hour with a sustained ebb flow and without waves. 



(c) Operation of the tide generator was resumed, and a nor- 

 mal tidal cycle was run with waves. 



(d) At the time of maximiom flood velocity, operation of the 

 tide generator was again suspended, and 1 model hour of sustained 

 flood velocity was run without waves. 



During the trial verification tests it was found that reproduction 

 of two of the above sequences of operation (requiring a total of 3 hours 

 each) resulted in an accurate reproduction of average annual shoaling of 

 the inner and outer bars, as well as duplication in the model of the pro- 

 totype locations of the bars or shoal areas. Thus, the empirical time 

 scale for bed movement was 6 hours in the model to 1 year prototype. 

 The characteristics of the waves used during the tests were derived by 

 numerous trial-and-error experiments on the model. The waves developed 

 empirically and in these tests were the results of progressive attempts 

 to reproduce in the model the rates and directions of bed movement that 

 occurred in the prototype, as indicated by hydrographic surveys and 

 dredging records. The hindcast wave climate served as a guide in the 

 selection of the model test waves, but could not be strictly adhered to 

 because of the distortions previously discussed. 



(8) Test Procedures . The five plans selected for testing in 

 the model had as a combined objective to find a solution to the two most 

 pressing problems for which the model study was authorized: relocation 



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