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USGS CMG InfoBank: Spits and Bars

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Comment: 10:43 - 12:04 (01:21)
Source: Annenberg/CPB Resources - Earth Revealed 24, Waves, Beaches and Coasts
Keywords: "Thomas Hartnett", sand-spit, bar, sand, bay, "long-shore current", coastline, beach, sand-spit, breakwater, dredge, transportation, deposition

Our transcription: Sand-spits and bay-mouth bars are common products of long-shore currents.
What happens is that the sand is being carried along the coastline, the beach sand, and when the coastline reaches, say, a right angle turn, an abrupt bend, the beach will tend to be carried still by that long-shore current straight along the coastline.
So that the beach will start building out in creating an extension of the beach that will not necessarily follow the bend of the coastline.
In this case, a sand-spit has formed off the end of this breakwater.
This wave tank shows how the sand-spit built up.
The waves strike the breakwater at an angle and bend around it into the harbor.
When sand is added, the waves carry it into the harbor where it builds up into a spit behind the breakwater.
To prevent the harbor from being sealed off, and the beach beyond from being deprived of sand, engineers installed a dredge to pump the sand back into the long-shore current, by picking it up in the harbor and dumping it further down the coast.

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Page Last Modified: Thu Oct 31 04:27:54 PDT 2013  (chd)