588 



developed and demonstrated which will determine the optimum con- 

 trol strategy drawing upon all of the aforementioned quality control 

 techniques. 



Physical models 



Physical models can be considered essentially as three types. One 

 type, and perhaps most dramatic and most expensive, is one m which 

 the complete water mass and its basin under consideration are con- 

 structed in a scale keeping with that of the natural configuration 

 and in which the natural forces working on that basin can be applied 

 and varied at will. This sort of model is used effectively by the Corps 

 of Engineers and a great deal of excellent information has been de- 

 rived from them. Of all of the possible modeling alternatives, this 

 is probably the most useful and, hence, should be the most widely 

 applied for each of the major estuaries and minor estuaries of special 

 interest in the country. Research is needed to obtain similarly reliable 

 information without going through the expense and time required to 

 construct these. 



Another kind of model is one in which a specific machine is devel- 

 oped and constructed which will reproduce certain of the natural 

 phenomena in the laboratory. These normally are flumes, wave basins, 

 or some other single-phenomenon simulating device. 



Utilizing these laboratory simulation devices, the following studies 

 should be conducted. 



(a) Large movable flume tests using the typical range of 

 littoral drift material (sand and shell) found along the coast are 

 essential to verify or modify the various sediment transport 

 formulas; determine lower and upper limits for application of 

 such formulas; improve definition of roughness coefficient with 

 changing geometry, sand riffles, and dunes ; and determine definite 

 usable values of entrainment functions and tractive force (bot- 

 tom shear stress) . 



(b) Utilizing three dimensional wave basins, studies should 

 be done to help yield first approximation designs of inlet and 

 inlet model studies to help locate and determine the size and shape 

 of jetties; determine effects of winds and waves on tidal flow, 

 erosion, siltation, sediment transport, and sand bypassing; and 

 check the effects of density currents on flow and sediment trans- 

 port. Information of this kind allows a revision and refinement 

 of inlet designs. Studies should be done to determine the effects 

 of changes in tidal differentials, changes in circulation and effi- 

 ciency of mixing, and structural modifications for controlled 

 water releases, for restoring and improving internal circulation, 

 for enhanced fishery environments, and for augmented assimila- 

 tion of treated return flows. 



A third method of physical modeling is to use a portion of an actual 

 estuary. Such model estuaries have the dual advantages of providing 

 both a natural environment and a means of control over many variable 

 factors. Model facilities are built outdoors in a relatively unpolluted 

 bay near its mouth. Proximity to the open ocean assures waters with 

 salinity values sufficiently high to supjwrt a wide variety of organisms 

 the year around. Adjustment of salinities is accomplished by adding 



