On the nature of estuarine circulation : part I (chapters 3 and 4)

The reader will quickly see that the subjectmatter of Chapter 3 is confined to the hydraulics of sharplystratified media, whereas real estuaries are always more orless diffusely stratified. What is more, no discussion ismade of the order of magnitude of the friction terms. Inordinary single layer flow (such as in rivers) engineers already have crude approximations of the friction terms (Chezyand Manning formulas), but we do not have even these approximations for two layer flow. For this reason the differentialequations of gradually varied flow of two layers are for themost part left unintegrated and all that is demonstrated isthe qualitative aspects of the flow.In the case of entrainment of water from one layerinto another we can only perform integrations of the equations when the amount of entrainment is known, whereas in real estuaries we do not have a priori knowledge of this amount.The reader will see, therefore, that the subject matterof Chapter 3 is really very incomplete, leaving undetermined all the constants which depend upon turbulent mixing,upon the frictional stresses on the bottom, and thefree surface and the walls, and upon the amount of entrainment.The contents of Chapter 4 are somewhat different.First of all, they contain summaries of severalof these papers have proceeded on the basis of hypotheses already published papers on the mixing in estuaries. Mostabout the nature of the mixing process. The applicabilityof these hypotheses appears to be restricted to only certain estuaries, and it must be admitted that more work hasbeen done that involves guessing what the mixing processesin an estuary might be, than has been done in trying tofind out what the mixing processes in an estuary actuallyare.As incomplete as the subject matter of Chapter 4is, it is hoped that it will suggest which of the possiblemixing processes in estuaries may be important in any particularone which is the subject of study, and that it willalso suggest the type of observations which will be mostdesirable in studying a particular estuary. For example:in an unstratified estuary it seems that a more or lessuniform spacing of stations up and down the estuary is desirable; but in an estuary which appears to be subject tothe constraint of overmixing (Section 4.51) the location ofstations should be largely confined to control sections.

Office of Naval Researchunder Contract No. N6onr-27701 (NR-083-004).