Problems and Opportunities in the Design of Entrances to Ports and Harbors Proceedings of a Symposium (1981) / Chapter Skim
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Sedimentation in Harbors
Sedimentation in Harbors
Pages 101-114
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From page 101... ...
In such harbors, the fresh river waters keep the clays moving; consequently, the principal sedimentation problem becomes one of sand. Dredging, training walls, and diversion of the river, are the usual corrective measures in such harbors.
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From page 102... ...
Sand Transport by Littoral Currents General Considerations The result of waves breaking at an angle to a shoreline is generation of an alongshore or littoral current. It is this current, combined with the agitating action of the breaking waves, that is the primary factor causing the movement of sand along a coastline.
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From page 103... ...
Undoubtedly, the drift occurs in one direction along the various coastlines at certain times of the year, and in the opposite direction during the remainder of the year; however, a net drift occurs in the direction and at the rate indicated. For example, along the south Atlantic coast of the United States the littoral drift is northward during the summer season when light winds from the south and southeast prevail, but during the fall and winter, strong northeasterly storms, accompanied by relatively high seas, drive the sand southward.
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From page 104... ...
10,000 aTransport rates are esti - ated net transport rates, Qn In some cases, these approximate the gross transport rates, Qg. bMethod of measurement is by accretion except f or Abeecon Inlet, and Ocean City, New Jersey, and Anaheim Bay, California, by erosion and Waikiki Beach, Hawaii, by suspended load samples.
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From page 105... ...
At localities where these two currents are opposed, the wave-induced littoral current usually is the stronger of the two, and therefore determines the predominant direction of littoral drift. Sediment Transportation, Deposition, and Erosion at Man-Made Littoral Barriers There are three basic types of man-made coastal structures that function as littoral barriers: a dredged channel, a jetty or groin, and an offshore or detached breakwater.
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From page 106... ...
As the upcoast fillet approaches equilibrium, littoral material will move along the outer face of the breakwater and be deposited in the relatively calm water in the lee of the structure. Thus, the turbulent character of the wave action upcoast from the breakwater tip is sufficient to transport littoral material at capacity.
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From page 107... ...
Schematic representation of transportation, deposition, and scour of littoral sediments at channel dredged through littoral zone.
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From page 108... ...
In the case of natural inlets that have a well-clef ined bar formation on the seaward side of the inlet by way of the outer bar, but intermittent, rather than regular, supply reaching the downdrift shore, the result is that the shore downdrift from the inlet is normally unstable for a considerable distance. If the strength of tidal flow through the inlet into the interior body of water is appreciable, part of the available littoral drift is permanently stored in the interior body of water in the form of an inner bar, reducing the supply available to nourish downdrift shores.
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From page 109... ...
Bahia Blanca. Harbors in tidal estuary.
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From page 110... ...
The large estuary of Bahia Blanca has no streams of any importance feeding into it: the sources of sediments are the Rio Colorado, the Rio Negro, or both. Notice that whatever the direction from which waves come -- south, southeast, west, even to some extent, northeast -- littoral drift will occur along the coast, moving material into the entrance of Bahia Blanca.
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From page 111... ...
Pier built parallel to tidal stream. am_ _e Hi_ ~ Figure 12.
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From page 112... ...
The principal tidal currents keep the main channels open, but the accumulations of fine materials eventually become cohesive sediments at the entrance to the tug harbor, which is somewhat restricted. The flow of sediments from the mud flats (Figure 12)
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From page 113... ...
In the particular case you refer to, there isn't any parking area in that main stream, and if you dredge a parking area from the mud flats, it will eventually fill up; nonetheless, T agree with your point. BERTSCHE: Would knowledge of the whole hydraulic water flow of that area at the design stage help you in solving some of the sedimentation problem" that occur?
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From page 114... ...
Between Santa Barbara and the Channel Islands Harbor, for example, is the Santa Clara River, which can get out of hand about every 25 to 30 years, suddenly dumping a huge amount of material just up the coast from the Channel Islands Harbor. HERBICH: You mentioned some equations in the Shore Protection Manual that allow one to make estimates of Sediment transport.
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