III. ESTUARIES 



Frank A. Eervmccnn^ Jr. 



Introduction. 



The term estuary is classically defined as the lower reaches of a 

 stream (a river or a creek conveying upland discharges) where the effects 

 of the tide may be distinguished; i.e., where a periodic rise and fall of 

 the water surface may occur in consonance with the astronomic forces 

 alone, or where periodic reversals of current direction may also occur. 

 Recently, much broader definitions of estuaries have developed. One 

 broad definition (used in this report) describes all coastal waters from 

 the ocean to the limits of tidal effects as estuaries, to include bays, 

 rivers, creeks, fjords, coastal inlets, straits, sounds, lagoons, laby- 

 rinthine mazes of channels meandering through marshes and deltas, and 

 artificial canals (only if the canals exhibit tidal effects). (U.S. 

 Army Engineer Waterways Experiment Station, 1969.) 



Estuaries are immensely valuable resources, which serve as habitats 

 for migratory waterfowl, fish, and shellfish, as sources of water supply, 

 and as arteries of commerce; thus, their preservation is of great im- 

 portance. In a natural condition, before man altered their characteris- 

 tics, estuaries were much more satisfactory for wildlife and as sources 

 of water supply. However, as commerce began to grow and ship sizes in- 

 creased, natural channels were inadequate, and it became necessary to 

 enlarge and straighten the channels at critical reaches. These initial 

 works, which were relatively minor in scope, were often ineffective. 

 Historically, the first estuarine problems were associated with the need 

 to improve the waterway for navigation. The dimensions of the channels 

 required to accommodate the larger ships had to keep pace with increasing 

 ship size, and these enlarged channels began to create significant changes 

 in the regimen of the estuary (U.S. Army Engineer Waterways Ej^eriment 

 Station, 1969). 



Improvements in the interest of navigation pose a number of associ- 

 ated problems, and their solutions in turn give rise to other problems 

 which may be termed "side effects." Other problems, not related to navi- 

 gation, also arise due to increased populations and associated activities 

 along the course of the estuary; e.g., the problem of deterioration of 

 water quality. Popular demands to abate estuarine pollution are at a 

 very high level and are not likely to decrease until the associated 

 problems are resolved. Estuarine problems are broadly classified as: 

 (a) those indirectly related to, or resulting from, navigation or navi- 

 gation improvements, and (b) those due to factors not directly traceable 

 to navigation or to navigation improvements. Table 3-1 lists the estua- 

 rine problems for each classification (the order of presentation has no 

 significance) (U.S. Army Engineer Waterways Experiment Station, 1969). 



Hydraulic modeling is a problem-solving technique that requires the 

 development, construction, verification, and testing af a scale model of 



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