621 



Physical processes in estuaries 



It is necessary to develop a sound physical basis for quantitative 

 predictive models of time and space variations of constituent distrib- 

 utions in estuaries. This will require further work on theoretical, 

 numerical, and physical models, determining the correlation between 

 the models and field studies. Priorities need to be set based on the 

 urgency of the practical problem and the relative degree of under- 

 standing of the particular class of estuarj. The most urgent problems 

 are likely to occur in those estuaries which we know the most aibout, 

 primarily coastal plain estuaries. 



(1) Further knowledge is required of the relationship of the mean 

 circulation, tidal currents, and turbulent exchanges to the river inputs, 

 external tides, external density distribution, wind, and the shape and 

 size of the estuary. 



(2) There is little knowledge of conditions responsible for the 

 change in an estuary from a salt-wedge to a partially mixed estuary, 

 or from a fjord to either a salt-wedge or partially mixed estuary. These 

 conditions need study, particularly those in fjords. 



(3) In the development of models, both theoretical and numerical 

 models should be stressed as they include the possibility of the incor- 

 poration of biological, chemical, and physical processes at prototype 

 scales. 



(4) The turbulent processes need investigation as their dependence 

 on density stratification and mean velocity shear plays a dominant role 

 in the behavior of these estuaries. 



Turbulent fjux and diffusion 



(1) Detailed observational approaches to the problem of turbulent 

 diffusion are needed. Simultaneous measurements of turbulent fluctua- 

 tions in velocity, salinity, and other properties together with environ- 

 mental factors such as shears in mean velocity and stability of the 

 water column are necessary. Likewise, tracer studies on a scale of 10- 

 100 meters should be carried out under various environmental 

 conditions. 



(2) There is need to develop predictive models for gross spreading 

 of patches and plumes in the ocean from the combined effects of eddy 

 diffusion (both horizontal and vertical) and shear in the mean A^e- 

 locity field. The research in item 1 above will provide a basis for this 

 development and will allow a better interpretation of previously re- 

 ported values of gross dispersion coefficients. 



(3) It is recommended that systematic tracer experiments be car- 

 ried out in subsurface waters in order to have more reliable informa- 

 tion on the dispersion or rate of speed of a patch or plume. These 

 experiments should include the use of artificial tracers, such as fluo- 

 rescent dye, and studies of existing w^aste fields which occur at sub- 

 surface depths. 



Physical processes in coastal areas 



(1) To achieve a proper understanding of coastal circulation on all 

 scales, a program of collection of oceanographic and meteorological 

 data is recommended. The observations should be made over a long 

 enough period of time to reveal all periodicities up to and including 



