589 



fresh water from some nearby source such as a stream. Renewal of the 

 water in the facility is by natural tidal action through properly de- 

 signed tide gates. Currents of varing 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 

 water quality requirements of estuarine organisms. A corollary objec- 

 tive is to determine how various pollutants affect the water quality 

 requirements of estuarine organisms and ultimately their productiv- 

 ity. It is apparent that properly conducted, comprehensive studies of 

 this type would take a great deal of time, effort, and money. Significant 

 economies can be achieved in all of the latter if the model facilities 

 would be successfully miniaturized. Other advantages to the use of 

 miniaturized model estuaries greater flexibility in the study of vari- 

 able factors and a substantial reduction in the quantity of pollutants 

 required for testing. A basic requirement for such model facilities is 

 the ability to maintain on a self-sustaining basis the biota representa- 

 tive of the parent bay. Accordingly, the initial phase of study would 

 be concerned with developing the various size model estuaries to deter- 

 mine the degree of miniaturization possible without sacrificing the 

 basic requirements. 



Development and use of model estuaries would be especially suited 

 for supplying much of the water quality information identified by 

 the National Technical Advisory Committee on water quality require- 

 ments. It also would serve as a bridge between laboratory and field 

 studies and, as such, assume a priority role as a research need. 



Special values of physical modeling 

 The value of physical models of the tidal and estuarine environ- 

 ment lies in their adaptaJbility of use to study a wide spectrum of prob- 

 lems. Some of the most significant are: flooding due to hurricane 

 surges; efficiency of tidal mixing and the resulting salinity distribu- 

 tions; diffusion, dispersion, and flushing of waste discharges (sewage, 

 chemical, thermal, etc.) in bays and estuaries along the coast; shoaling 

 and erosion in bays, navigation channels, coastal inlets, etc., due 

 to deposition of dredging spoil, and river and coastal sediment move- 

 ments ; improvement and verification of designs for navigation chan- 

 nels, estuarine coastal structures, tidal inlets, jetties, etc. They 

 provide a means of determining in advance the effects of channel deep- 

 ening, jetty extension and construction of new jetties, the effects of 

 land fills and destruction of parts of tidal flats, and the effects such 

 projects would have on the total physical picture of an estuary. 



Mathematical models 



Mathematical models have the advantage of rec[uiring little expen- 

 sive construction and maintenance. They are basically expansions of 

 equations of state of various physicochemical phenomena in a water 

 course. They theoretically should allow for proper consideration of 

 all of the variables, when known. Simulation is done through computer 

 techniques and, hence, has the advantage of speed and flexibility. The 

 drawback in the application of these models is the need to know. 



