Seaside resorts would lose their popularity and their customers if they lost their beach.
Where the local council want to be sure to keep, and even build up their beach, groynes are often built – those wooden fences that point straight out to sea and can make a walk along the beach something of an obstacle course.
Groynes also provide a handy indicator of the predominant direction of the longshore drift. The beach material piles higher, and the waves don’t come in so far, on the side that has the most longshore drift moving towards it.
You can see the effect on this satellite view of Bournemouth.
So if your beach has groynes, then you need to go armed with a tape measure.
Measure from the top of the groyne vertically down to the beach material. Do two measurements at the same place, one on each side of the groyne. You’ll get a smaller measurement where there is a bigger pile of beach material and that’s the side that the longshore drift is coming towards most of the time.
Here are some things to investigate:
- Is the height difference bigger closer to the sea?
- Is the height difference bigger at one end of the beach?
- Is the longshore drift for a particular day (as shown by a float or pebbles) the same as the overall longshore drift direction (shown by the groynes)?
And don’t forget to check out the satellite view of your favourite resort.