But by the time it was completed in 1598, the Guadalquivir River had begun to silt up, causing all New World trade to move to Cadiz and the building became a rather opulent filing cabinet instead.

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Ian Barclay, a project manager on the silt scheme, said it would be good to add the extra barrier to stop the silt building up again so quickly.

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Staffordshire county council said the divers went into a culvert underneath the road and found blockages created by debris and a build up of silt and mud.

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The Canal and River Trust said silt would be "hoovered" up from the bottom of the docks.

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To be sure, the dam has helped Egyptian farmers irrigate year-round and has prevented periodic flooding, but it has also deprived the Nile delta of nutrient-rich silt, which instead just piles up behind the dam.

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You don't have the border barge traffic kicking up the sand and the silt.

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Dig up, suck up, that sand and silt then separate the heavier cassiterite from the lighter sand and silt.

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The cassiterite makes up some fraction of the standard sand and river silt there.

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The theory is relatively simple: Seawater and freshwater, filtered to remove silt, are fed into pipes which lead to a membrane system, made up of spiral coils to maximize surface area.

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Work is slow along the 525-foot-wide route to Umm Qasr's grain elevator, where the Dredge Carolina chews up the mud with its 3, 000 horsepower cutter and suctions out the loosened silt.

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