VI-152 



on flow and sediment transport. Infomatlon of this 

 kind allows a revision and refinement of Inlet designs. 

 Studies should be done to determine the effects of chan- 

 ges In tidal differentials, changes In circulation and 

 efficiency of mixing, and structural modifications for 

 controlled water releases, for restoring and Improving 

 Internal circulation, for enhanced fishery environments, 

 and for augmented assimilation of treated return flows. 



A third method of physical modeling Is to use a portion of an act- 

 ual estuary. Such model estuaries have the dual advantage of pro- 

 viding both a natural environment and a means of control over 

 many variable factors. Model facilities are built outdoors In a 

 relatively unpoHuted bay near Its mouth. Proximity to the open 

 ocean assures waters with salinity values sufficiently high to 

 support a wide variety of organisms the year around. Adjustment 

 of salinities Is accomplished by adding fresh water from some 

 nearby source such as a stream. Renewal of the water In the 

 facility Is by natural tidal action through properly designed tide 

 gates. Currents of varying velocities are maintained by the use 

 of recirculating pumps or paddle wheels. Various types of bottom 

 substrates are provided to meet the requirements of a wide variety 

 of benthic organisms. 



Studies using the above-described model estuary facilities provide 

 a controlled natural environment for determining realistically the 



