Here at the entrance of the harbour we are particularly vunerable to this, as the might of the Pacific Ocean funnels up through this narrow gap twice a day.
The beaches here 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 can been installed to contain the sand. 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 based on the natural effects and ignore the ships. Do not publish them as part of your log. You can log your find
1) In which direction is the sand prone to migration? What do you see that draws you to this conclusion?
2) Based on the above if sea defences are added which end on the beach you are standing on should they be put? Does this match the location the ones built in late 2021?
3) From where you stand describe how longshore drift has affected the shipping channel.
(Optional) include a photo of you or your GPS along the beach area.
Wish to attend New Zealand’s next large multi-day event? GCA7ZHD Geo Toroa will be held on NZ’s Labour Day long weekend 26-27th October 2024 right here in Dunedin. Details in the link below;
