Cave Flooding

[Graigwen]

Very heavy rain two or three times a year in the Blaenavon, Varteg and Pwll Du areas causes the free air surface in Lein Fawr (the main conduit taking water from Rifleman's Chamber in Ogof Draenen) to migrate upstream from somewhere near Snatchwood Risings to above Abersychan. This results in water pouring up out of Charlotte's Estavelle in the "Bouncing Field" at Abersychan inconveniencing her horses. The water flows at first along a shallow channel into the nearby Afon Lwyd.

As the underground water level falls, the free air surface moves downstream again and water from the flooded field pours back into the estavelle, so the flooded area drains very quickly.

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[Bratchley]

Thanks guys,

Doesn't seem to be a huge amount of impacts from it then! Been struggling to identify things myself.

Josh

 

[Fulk]

Doesn't seem to be a huge amount of impacts from it then!

I think that's the right conclusion; if there is enough rain to cause a flood, then it's going to flood ? with or without any intervention by caves. I suppose that in some situations water being channelled through a cave might slow down the effect of the rain ? on the other hand, I guess that some caves can transmit water more quickly than surface water course and speed up flooding, but overall I doubt whether they make much difference.

I suppose it's also possible that water could be diverted off in a different direction underground to that which it would have taken had it stayed on the surface. One example might be that of the water in Apedale Beck (I think) in Wensleydale, which sinks in Wensleydale and reappears in Swaledale, but I'd be surprised if that did much to lessen the impact of flooding in the former and increase it in the latter! And I imagine that such cases are pretty rare . . . e.g. if all the sinks associated with Gaping Gill were suddenly to close up and the water could no longer go underground, the streams would still drain down Trow Gill, for example, to Clapham ? where the resurgent water goes anyway.

 

[Graigwen]

Thanks guys,

Doesn't seem to be a huge amount of impacts from it then! Been struggling to identify things myself.

Josh

In the case I mentioned earlier, the Afon Lwyd, I suspect that the existence of a second, roughly parallel but underground, watercourse in some way mitigates flooding from the surface river. There are several points at which the two systems interact, and possibly others not yet recognised.

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[SamT]

Re impacts.. then no, there are few major impacts.  IMHO - this is because these things have flooded for time immemorial and generally, (notwithstanding housing estates on floodplains) people haven't built on the areas downstream of caves that regularly flood. 

As mentioned, man made alterations to water courses, (soughs, land drains, sewers etc) generally cause the 'unexpected' results. 

And there are always the '1 in 250 year' type events.

 

[Cave_Troll]

caves flood
normally due to factors like "more rain than usual in a shorter time"

is this a blame thing? are you looking to tidy the water flow by removing the cave from the system ? lawsuits against the owners of caves ?

 

[RichardB1983]

I suppose it's also possible that water could be diverted off in a different direction underground to that which it would have taken had it stayed on the surface.  e.g. if all the sinks associated with Gaping Gill were suddenly to close up and the water could no longer go underground, the streams would still drain down Trow Gill, for example, to Clapham ? where the resurgent water goes anyway.

But sometimes it can cross the natural surface watershed and end up in a different valley entirely.

For example the 'natural' surface direction for all of Peak Cavern's "P" swallets is down Perry Dale, through Peak Forest, Hay Dale, Peter Dale and Monk's Dale and into the River Wye at Millers Dale, instead of into the Hope Valley at the current resurgences. Granted it all ends up in the River Derwent eventually (and then the Trent -> North Sea), but if the P swallets were completely blocked, then Castleton would see much less flooding, and Peak Forest would be regularly inundated - especially as there's no surface stream there at the moment - so the A523 would be a ford even in low water conditions. Subterranean drainage has actually changed the size of the catchment area of each of the valleys

 

[Fulk]

caves flood
normally due to factors like "more rain than usual in a shorter time"

is this a blame thing? are you looking to tidy the water flow by removing the cave from the system ? lawsuits against the owners of caves ?

Or maybe the OP was simply interested in a somewhat esoteric notion?

 

[Amy]

If you forget to leave the diversion off when you leave in Mystery Falls the water overflows onto the highway below causing a rather impassible torrent in the right weather. TDOT had to get one the local keyholders to scuba in and fix it once (entrance sumps).

 

[Amy]

Also if you remember Hambrick cave we took you to on kayak to see the bat flight, thats been largely flooded when they built the dam we put in at. They had to do extensive surveys as that and the other now flooded caves there were historically significant native american places. Lots of excavation and survey required prior to flooding it.