£. Movable-Bed Distorted-Scale, Complete Model . This model is essen- 

 tially as effective as the movable-bed sectional model for investigations 

 of shoaling and scouring in the inlet, except that the sectional model is 

 more adaptable to operational requirements. The model allows investiga- 

 tion of bed movement within the bay; however, techniques do not presently 

 exist to allow investigations of shoaling and scouring trends from approx- 

 imately the throat of the inlet oceanward at the same time as shoaling and 

 scouring trends in the bay. Different model operating procedures and usu- 

 ally different movable-bed model materials are required for these two areas 

 of investigation. Both movable-bed models require extensive prototype data 

 collected over a period of several years to obtain an adequate verification 

 of the model. 



2. Planning for a Model Study . 



The most important point concerning an effective model study is that 

 the results can only be as accurate as the prototype data on which the 

 model study was based. This requires that prototype information be 

 available at critical times during the course of the model study. Un- 

 fortunately, the normal model study must be undertaken without this in- 

 formation, with resulting adverse effects on time and costs unless proper 

 planning is maintained to obtain information during the study. The need 

 for proper planning as well as the effect of prototype data input to a 

 model study can be demonstrated by two modified critical path charts 

 shown in Figures 7-1 and 7-2 for studies of tidal inlets. The times 

 shown in the charts are only estimates which can vary considerably for 

 specific inlet studies; however, the time frames are sufficiently accu- 

 rate for demonstration. 



In the epcample charts, the assumption is made that the study will be 

 directed toward defining, in detail, conditions in or near the throat of 

 the inlet and that definition of effects outside this area will be lim- 

 ited to gross tidal prism changes only. Specifically, the example model 

 will be used to evaluate the effectiveness of plans to stabilize the 

 navigation channel through the inlet, define the hydraulic conditions 

 for existing or proposed conditions, evaluate the effectiveness of sand- 

 bypassing systems, and define the effects of the proposed improvement 

 works on the tidal prism in terms of total flow through the inlet. Sim- 

 ilar charts can be prepared based on specific purposes of model studies. 



The tasks represented by each block in Figures 7-1 and 7-2 are dis- 

 cussed below. 



a. Block 1 . This is the designated starting time based on a deci- 

 sion to conduct the model study. At this time, all preliminaries have 

 been completed; the purpose and scope of the model study have been de- 

 fined, and the need for the model investigation confirmed. 



b. Block 2 . Model studies of this type require both shelter space 

 and associated plant equipment, such as tide generators, wave generators, 

 movable-bed sounding systems, water level recorders, and velocity recorders. 



457 



