phenomena would be con^) lately irrelevant and others would be so nearly- 

 irrelevant as to be negligible. The recommended approach to the design 

 of an estuary model would be to first select the prototype phenomena 

 which would significantly affect, or be affected by, the problem to be 

 studied (or by possible solutions) , and then to design the model to simu- 

 late the selected phenomena with acceptable accuracy. Since equations 

 cannot be developed to express the highly complex interrelationships be- 

 tween the many variables involved in the modeling of a major estuary, 

 extensive prototype data collection programs must be carried out to 

 support adjustment of the model to attain and prove the necessary degree 

 of similitude. 



The use of hydraulic models to predict the effects of construction in 

 estuaries began in 1885 when Professor Osborne Reynolds constructed and 

 tested a small-scale model of the Mersey Estuary in England. This model 

 was constructed with an erodible bed of sand, molded initially to an 

 earlier hydrographic survey of the estuary, and was operated through a 

 great number of tidal cycles to determine if observed changes in channel 

 and shoal conditions could be reproduced as observed in nature. Professor 

 Reynolds concluded that the model reproduced known changes in bed config- 

 urations with enough accuracy to be used for prediction of future events; 

 consequently, the remainder of his study involved installing a variety of 

 possible remedial works in the model and testing to determine which plan 

 or plans produced the most desirable channel conditions in the estuary 

 from the viewpoint of developing channels for navigation (U.S. Army 

 Engineer Waterways Experiment Station, 1969). 



The first estuary model at the U.S. Army Engineer Waterways Experi- 

 ment Station (WES) was constructed for Winyah Bay, South Carolina, in the 

 early 1930' s. This study was followed by several other model studies of 

 tidal inlets and parts of estuaries; however, all of these models repro- 

 duced only relatively small sections of the systems involved, and were 

 equipped with flow and elevation control devices at each end to simulate 

 the dynamics of tidal flow in the problem areas. The trend toward con- 

 structing large, ocean-to-river comprehensive models of estuaries at WES 

 began about 1940, when it was realized that density (salinity) phenomena 

 played a significant role in estuarine hydraulics and in the resultant 

 sedimentation and flushing characteristics of estuaries. Accordingly, 

 model laws and techniques were developed for operating estuary models 

 with both saltwater and freshwater, as well as for adjusting the resist- 

 ance of the models in such a manner that both vertical and lateral current 

 velocity distributions of nature were reproduced to scale in the models. 

 As a result of these developments, it is now possible to reproduce (with 

 acceptable accuracy) the distributions of both current velocity and 

 salinity throughout the models, the resultant density-induced vertical 

 circulation that exists in nature, and the extent of saltwater intrusion 

 as affected by tide and freshwater inflow (U.S. Army Engineer Waterways 

 E^qjeriment Station, 1969) . 



After a physical model has been properly adjusted and verified, many 

 of the effects of planned construction in the estuary involved can be 



51 



