Dear Nelly,
It is surprising to what extent people go to
restore beaches, when efforts are doomed to fail, while neglecting them
when they can still be saved. I guess that intensive use and greed cause
both loss and the interest to save. And ignorance of course.
The sand in tropical coral beaches (calcium carbonate) is much lighter
than the silica (SiO2) of your beaches. Coral sand is very easily moved
by small waves, and is mopped towards the beach much more easily. But it
does not move readily in the wind, so no dunes are made.
The sand lost off Florida beaches has not gone anywhere distant, and
certainly not off the continental shelf. There is a kind of stupidity
going on here. Engineers prefer to replenish beaches with large grains
because these do not move around in the wind, and likewise, won't be
sucked away by fairweather waves. However, storm waves are sufficient to
move them as the beach lays itself flat to absorb the storm's energy.
Sand is thus moved away from the dry beach to the wet beach because the
waves are sufficient to move the larger grains. However, when natural
recovery is needed by fairweather waves, the waves' energy is
insufficient to move the coarse sand back up the beach. Gradually the
coarse sand sinks underneath the fine sand. It is a bad policy, inspired
by ignorance of the beach-dune system.
Beaches like those in Florida are indeed doomed, and replenishment is
just such a stupid idea. Please study the efforts of the Danes in
de-watering beaches. It involves an invisible pipe along the beach well
beneath high tide level, sloping towards a draining point. From there
the water is pumped up and discarded. See the Seafriends web site re
engineering solutions, for more detail. De-watering is cheap, invisible,
requires little energy, and WORKS. De-watering dries the beach where it
can dry, so that the natural forces of wind and sunshine can do their
restorative work. It won't cost much to give it a try.
Notice that this does not work for tropical beaches, because these have
no 'dunes' and are merely an 'overwash' situation.
You may also be interested in my recent discoveries explaining the
mysterious killer called 'eutrophication'. Read the DDA chapter.
http://www.seafriends.org.nz/oceano/beacheng.htm#drainageCheers,
--
Dr J Floor Anthoni; 55B Glenvar Rd; Torbay; Auckland 09 4735433
Director Seafriends Marine Conservation and Education Centre
7 Goat Island Rd; Leigh R.D.5; New Zealand
Ph +64 9422 6212 Fax: +64 9422 6245
Seafriends web site:
http://www.seafriends.org.nz/
