Hydrology question

[phillip1]

So we found a major new spring here, I found it a month ago more or less and at that time it had been raining non stop for about 2 weeks and there was absolutely no way to dive tis thing as a major river was coming out of it, we went there yesterday and dove it, very cool looking and after a while we surfaced in a massive dry cave canyon like 5-6 meters wide by 50-60mtrs high, around the corner there was a slope and a huge underwater vertical canyon with so much flow I did not even try to get in anyway we were both at thirds so swam out.

My question is this, this spring is at an altitude of 350mtrs and the mountain only goes up another 300 meters and then goes straight down the other side in other words there is no long slope in front of it so I do not understand how so much water can accumulate and create such flow.

It has not rained at all not even a bit in that area for over 3 weeks so how can so much flow still be present and were does it come from, what makes such a high water pressure if there is zero rain and no mountain or even much terrain in front of the spring?

[rjack]

Is there another mountain (nearby-ish) on the island from which the hydrostatic head originates?

[phillip1]

not near this one, the weird thing is that according to the locals there is always at a bare minimum the amount of water coming out as we had yesterday, in extreme drought one of the locals said it might get a tiny bit less but is always flowing pretty strongly.

[jlillest]

Rain makes a spring flow higher than normal but the base flow that you're talking about comes from the saturated soil absorbing water from rain storms and then slowly releasing water over time. The only way to fully determine the full watershed for a karst system is to dyetrace all the potential sink points across the mountain to get a feel for the drainage. I'm not familiar with the geology in the DR, but I'm betting it's similar to PR in that there isn't much in the way of caprock. (If that assumption is correct, you'll have a more difficult time finding major sink points)

In Virginia we have fun mapping out the watersheds, and it's a lot simpler for use because we have a lot of caprock and it's easy to find major insurgence points. On one mountain up here, you can walk for miles across the limestone/sandstone contact and cross lots of sinking streams. I have a friend that can tell you where each and every one them goes too, it's fun to think that that one mountain feeds 5 major karst springs with over 70 miles of known passages.

Here's a good primer on cave geology that should explain some more:
Cave Geology by Art Palmer

-Jon

[Webmaster]

I assume you're asking about how there could be so much water coming from a cave that high, with a limited catchment area?

If there's not additional head somewhere in the distance to drive it, it's possible it's just coming from an extensive perched source there on the mountain. I'm guessing there isn't much in the way of regular surface streams up there?

Also, the direction the cave seems to be taking doesn't necessarily mean that's the direction the water is ultimately coming from.

[phillip1]

I assume you're asking about how there could be so much water coming from a cave that high, with a limited catchment area?

Exactly! why could I not have asked the question like that.lol the catchment (a new word for me) area is very limited and the weird thing (to me) is that this is were a major river in that area is born, so to speak. in the air dome part were we turned the dive it looks like a massive canyon carved by major outflow as does the rest of the tunnels.

the spring head is at the end of a big canyon obviously carved by a lot of water and people go river rafting there in the winter, being so high up with very very little catchment, now I can understand when it rains were the water is coming form but I really do not understand were so much water comes from when it does not rain at all for months on end.

[OFG-1]

Phillip,

What is the earth made of up there, is it silts, sands, clays or all rock? There are different permeability constants for the different soils. There are clays that are so fine that it takes months for water to percolate through them a few meters.

[phillip1]

it is all limestone

[OFG-1]

it is all limestone

Well, then only theory that I have is Bermuda Triangle interference with normal gravity. Either that, or the resurgence of the main sewer system for Atlantis.

[FW]

it is all limestone

He is asking what type of soil is over the limestone. The entire recharge area can't be all limestone, or there wouldn't be any plants growing on it.