Problems and Opportunities in the Design of Entrances to Ports and Harbors Proceedings of a Symposium (1981) / Chapter Skim
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Tidal Hydraulics
Tidal Hydraulics
Pages 115-132
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From page 115... ...
It is emphasized that the term Tidal hydraulics" has come to be understood as including, in addition to the purely hydrodynamic considerations of such tidal waterways as inlets, estuaries, maritime straits, and canals, the following: channel dimensions and alignment; shoaling, including consideration of sources of the sediment, manner of transport, and cause of deposition; training works and dredging procedure (but not dredge design) ; jetty and breakwater layout; the salinity of the water, including associated phenomena; and the dispersal and flushing of pollutants.
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From page 116... ...
Tidal conditions within a waterway depend basically on the exciting tide, the shape of the waterway, and tbe bottom friction. In a converging waterway, where friction is a secondary factor, tidal amplitude increases as the tidal wave progresses upstream.
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From page 117... ...
Typical semidiurnal tide of East Coast (1) , and typical mixed tide of West Coast (2~.
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From page 118... ...
, · , , ~ ~/DE 1 2 3 4 5 6 7 8 9 10 1 1 12 TIME, HOURS DELAWARE BAY Fig~re 5. Typical tide-velocity relation.
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From page 119... ...
They affect the basic tide independently of the effects of geometry, greatly modify the resultant current by lengthening the ebb and shortening the flood, transport upland sediment to the tidal waterway, and interact with salinity intrusion forces to produce density currents. Additionally, the inflow of fresh water is the means by which a tidal waterway purges itself of pollutants introduced by man, and variations in the freshwater discharge rate alter the extent of salinity intrusion, as shown for the Delaware estuary in Figure 6.
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From page 120... ...
FRESH WATER I SALT ~ VATER ~O =~000~2 44 FLOOD EBB FLOOD EBB TYPIGAL DISTRIBUTION OF VELOCITY IN HIGHLY STRATIFIED ESTUARY Figure 8.
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From page 121... ...
The extent to which the wedge intrudes upstream depends on the freshwater discharge, the channel depth, and the density difference between the flab and sea waters. Typical velocity distributions in a highly stratified estuary are shown in Figure 8.
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From page 122... ...
Conditions typical of wellmixed estuary. FRESH WATER ~ 4 2 O 2 ___ fLOOD EBB 1~(PICAL DISTRIBUTION OF VELOGITY IN WELL MIXED ESTUARY Figure 12.
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From page 123... ...
As in the highly stratified case, the upstream extent of saltwater intrusion is dependent on the freshwater inflow, as can be seen in Figure 13. The partly mixed type is obviously an intermediate step between highly stratified and well mixed (Figure 14~.
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From page 124... ...
\ l \ ~ HIoH ~TIDt \ ~ 20 - ENTRANCE ~o \\~/GH T/DE LOW _,>< \ 1 ~ \ I I / 1_ 1/ t _ SAL7 WAT ER O t / 1, 1. zo ~w 0 J 40 60z 80 ~ FLOOD E 68 100 TYPICAL DISTRIBUTION OF VELOCITY IN PARTLY MIXED ESTUARY c, 6 z o ~ 2 l~ n I,~ V ~ 2 : ~BB / - - 1 1 1 1 1 TOTAL AREA SUBTENDED BY BOTH EBB AND fLOOD CURVES =TOTAL fLOW 2 0m Z 2 o 4 AREA SUSTENDED BY EBB CURVE DIVIDED BY TOTAL 43 I3J AREA-PERCENT OF TOTAL FLOW DOWNSTREAM 6 1 1 1 1 1 1 6> 0 2 4 6 8 10 12 TIME IN HOURS ~FL OOD ~oo 0 20 40 SALI N ITY, P PT 10 M I L ES UPSTREAM COMPUTAT I ON OF FLOW Dl STR I BUTI O N SAVANNAH HARBOR Figure 16.
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From page 125... ...
u Fo = Froude number =v~;~; uO is the maximum flood tide velocity at the ocean entrance, and h is the mean depth of the estuary Of = freshwater discharge T = tidal period The degree of stratification increases with decreasing value of the estuary number. An estuary may be changed from bighly stratified to partly mixed or well mixed by reduction of the freshwater disabarge; conversely, one may be changed from well mixed or partly mixed to partly mixed or
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From page 126... ...
The result defines what percentage of the total flow per tidal cycle at that point is directed downstream, and is referred to as the ebb predominance. At the bottom of a saltwater wedge, the flow predominance can be 100 percent upstream; while in the freshwater layer at the surface, it can be 100 percent downstream, as shown in Figure 18.
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From page 127... ...
~ 75r ~1 1 1 1 1 1 17~ 1r z 3 o o ~50 o z = 0 - MEANTIDE ~ ~~ z _ RIVER O~5670 CfS ~_ ~_ ~ _ ~ I I ~ I I ~ ~ 25 __ 93 1 13 133 153 173 ~3 1000 Ft CHANNEL STATIONS RELATION BETWEEN NORMaL SURFAGE AND BOTTOM FLOW IN SaVANNAH HARBOR ,'A/~EL ~O~L/NG VFRY \ /~/F~VY/W TH/S~F~CH ~ _ ~, , `, _ 50 Figure 19.
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From page 128... ...
First, the salt water probably causes flocculation of suspended clays, which prevents them from being carried to sea in the upper flow layer. Second, density currents can move sediments upstream along the bottom to the vicinity of the flow predominance null point.
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From page 129... ...
g I , e ~E~r~ . t"D o .d / ~/ J / w CEN JE~ 3 _ 4,2 51 / / ,' 923 192S 193 t932 1939~1944 ~1ff4 PAST AND PRESENT SHOALING CHARACTERISTICS Of SAVANNAH HARBOR Figure 25.
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From page 130... ...
Thus, there was an upstream shift in the region of heaviest shoaling but relatively little increase in the total volume of annual shoaling. The early upstream migration of the major shoal area was not a significant problem because disposal areas for dredged material from earlier dredging operations were readily available.
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From page 131... ...
SEARLE: Yes, T can cite you cases of looking for a sunken barge. If you look for it at a particular time in the tidal cycle, you will find it.
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