Tannic water

[chip182]

Hi guys

We are looking at some potential new dive spots in the south island of N.Z and the water looks very black....... are these pools stained with tannins? we do not usually get tannic water here so i am a little stumped (most of our caves are fairly high flow resurgences)

-If these are tannin stains is it safe to dive in? i know hydrogen sulphide could be a problem.

-What is the visibility likely to be?

-Can anyone show me pic's of what tannic water they have dived in (prefferably surface and underwater shots).

Any help is greatly appreciated

[SuPrBuGmAn]

I didn't know New Zealand was part of Wakulla County, looks like some of the holes down here...


Tannic water can be clear, or very much not clear - particulate is a huge factor. Tannin cuts down ambient light a hellovalot faster. Sometimes there's nice clear spring water under tannic water.

[chip182]

I'm glad it looks like wakulla country!!!!! we're still yet to go and have a look but i'm really hoping there is some passage down there. there are over 40 sinkholes within an hour or so drive of this one and they are all still virgin!!!!! cave diving really hasn't taken off over here.

So i know this is a bit of an open ended question but how often does the tannic water separate from clearer water? There is some clear water close by and research suggests it is all within the same aquifer.

Thanks for your help

[mpoucher]

The tannins get in the water from surface run-off through organic materials (leaves, etc.) so when we get a lot of rain in Florida, the rivers will run black. During droughts the river levels go down and clear ground water will start to mix in and the rivers get clearer. I've seen temperature differences create lenses where cold tannic will sink below clear groundwater, or very warm tannic water will be on top of clear groundwater. Rain can do the same thing in some cases. We also have seasonal turnovers where surface water cools and sinks and forces the groundwater up.

[chip182]

thanks thats really helpful.

we have really cold clear groundwater in this area (the springs are a chilly 4 degrees celsius or 39 degrees Fahrenheit) so hopefully the tannic water is warm and floating, i just hope it does not rain before the trip we have planned as well!!!! you can see from the pics that there is a fair amount of vegetation in the area.