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How to spot sand on the move
There are many features on the beach that show you how sand nearly always moves in the same direction. The movement of sand along a beach is called transport. Some kinds of transport are natural, and some are man-made. Natural transport is called longshore drift.
Picture 3 shows a beach from the air. A lot of sand (brown colour) is being churned up by the water. You can see how the waves are pushing it to the left.
Picture 4 shows a new beach built across a bay by the settling out, or depositing, of drifting sand caught in the waves.
Sand being driven to the left
Drifting sand can cause problems for seaside resorts, and they often try to trap the sand by building fences – called groynes – in the beach (see also page 37). These fences are ideal for spotting the direction of drift (picture 5). The sand will be piled up against the side it is being carried toward.
When drift works
Waves will carry sand all year long. Big pebbles will only be carried during storms.
Sand and pebbles drift in the same direction as the wind blows. So, if the wind blows from the southwest for most of the year, the sand will drift, on average, towards the northeast, and so on.
Waves blow at an angle to the beach
G 4 A beach almost closing off an estuary. This kind of long beach is called a sand spit. This example is Stinson Beach, California.
G 5 Beach fences (groynes) can be used to find out the direction in which beach sand is drifting.
Sand trapped by groyne.
F 3 From the air you can more easily see sand being carried along by waves and currents. Notice that, although the land has changed direction, the waves and sand have not. As the waves carry the sand into deeper water, it settles out. Where the sand settles, a new beach begins to form. This is Santa Monica, California.
Less sand behind groyne
Beach groyne
Drift of sand due to waves.
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