bullinachinashop wrote:been meaning to ask for a while:
part 1 - Ive never really understood how ocean tides affect the temperature of the sea. especially around Sydney. Can anyone explain or post a good link?
part 2 - why do they close beaches? again, im looking for a sydney centric answer if you please
1. ralphy will be able to give a better answer about the tides, but essentially it is about the disturbance and distribution of different temperatures of water 'layers'. Have you done SCUBA diving? Off South Head is a classic for some reason - when you are going down to depth or coming up particularly (cos is slower) you can see through your dive mask certain 'wavy' layers in front of you. these are where water layers of quite different temperatures are laying on top of each other. These are called "Thermoclines". We dive with temperature measuring gear and it shows the immediate changes. Tides bring in these different layers of water as one body.
Further to this, you will likely be well aware that as you go deeper, the water usually gets colder. When the tide brings water in , it doesnt descriminate between cold and comparatively warmer water.
Thirdly you are looking at the tides affecting currents. How many times have you paddled out on your boog and felt yourself go through 'cold' or 'warm' patches (apart from where your mate just peed in the water..haha). a tide can push in or pull out a current of a particular temperature.
2. Closing beaches... this is up to the discrimination of the life guards on duty. Essentially it is about currents along the beaches, especially rips, which I'm sure you have heard of. Rips and gutters can contain powerful currents which can drag swimmers out of their comfort zone ... which usually means trouble.
Sydney - wise i dont know where you are, so I'll give some quick examples.
1. tamarama - where my boog club is. to look at pretty tame, but it is supposedly one of the most dangerous patrolled swimming beaches on the east coast (statistically). This is because it gets a massive cross current which at one end drags swimmers into a cliff with recesses under it (like small caves sort of) and the current swirls there and traps them, on the other end it will drag them out and around the reef and leave the waves to smash them into the front o the reef. Also for a beach break I have had some massive hold-downs for no particular reason. Not long ago there
was some decent swell around - not massive and I thought it was a fair paddle out - and one of my mates, who takes big stuff on said it was one of the hardest paddles of his life... just weird there.
2. South Curl Curl. Now there is a freaky spot... the NB guys here will know it. If the swell/current combination runs a certain way, it will take someone out along the rocks like a rocket - or bale them up in the corner - I have been there in storms and it gets crazy.
So there are a couple of examples from a sydney perspective - the idea of 'closing' a beach is to protect the public from themselves. Bronte gets some hell strong currents and it isn;t rare to bring folk in on my booger when the beaches are unpatrolled (I'm often out after the flags are down - and always when the beach is closed - cos is usually storm - yew!) , one chick was trying hard to drown me at the end of last season panicking.... had to organise her and her boyfriend at the same time...
Hope that helps a bit mate.. ask more if you want more specifics and I'll see what i can pull out of the bag.