The beaches of Poole Bay, in the Boroughs of Poole, Bournemouth and Christchurch are prone to a geophysical process known as Longshore Drift. This is caused when the prevailing swell direction is at an angle to the face of the beach. Sand grains are drawn back from the beach in a perpendicular direction and then pushed back at the angle of attack of the prevailing swell. The following diagram shows this.
To ensure that all the sand does not disappear sea defences have been installed to contain the sand. If you look westwards down to the beach from your vantage point you will see a series of groynes (effectively wooden barriers) that each stretch seawards approximately 100m. These protect the beach from the prevailing swell and prevent the drawback of the sand.
To log this Earthcache you need to email the Cache Owner with the answers to the following questions.
1) In which direction is the sand prone to migration? What do you see that draws you to this conclusion?
2) Looking west, how many wooden groynes can be seen before the first one that comprises of rocks. It's a fair distance, binoculars may be useful!
3) At the far west end of the beach at Sandbanks the drift is reportedly in the opposite direction. Please submit a reason why this might be? You may need to look at a map of Poole Bay to assist you with your answer or get Google to help, but there are some hints in the text above.
4) Approx 10m & 20m west of where you are standing there are signs that forbid the undertaking of two different hobbies. Please state what these are?