Cave Hydrology

Although rare, extreme pulses have been witnessed in the Lower Bung during very dry conditions. These are likely to originate from Main Rising. In 1993 two members of the Cave Diving Group were digging at the Backwater Choke in the Long Bypass having entered the cave via Peak Cavern and Treasury Sump. On the way in it was noted that the streamway was incredibly low, nothing more than a trickle. While at the choke it became obvious that something was happening in the cave. The trickle of water that runs under the choke rose to a flow and the main streamway could be heard roaring in the distance.

Upon investigation the main stream was found to have risen to a torrent. It would not have been possible to head upstream against the flow. The two options were to exit the Lower Bung via Egnaro Aven or via Treasury. Both involving a committing trip downstream with the flow. A decision was made to go for Treasury via the Long Bypass. Upon joining the main streamway it became obvious that this could only be a one way trip. Heading downstream to Treasury both cavers were swept off their feet on several occasions. At Treasury the diving cylinders were hastily grabbed and an exit was made to the safety of Peak Cavern. During the 25 minutes it took to get from The Backwater to Treasury there was no sign of the pulse abating. While still underground it was assumed that there must have been sudden, heavy and prolonged rain. Exiting the cave, it was dry, and there had been no rain.....

This pulse had occurred after a long period of dry weather. and this was obviously one of the pulse switching events and It seems more plausible that Main Rising was the source of the pulse rather than Whirlpool. The volume of water discharged was massive and prolonged. Anyone caught downstream of a way out would have been in serious trouble.

References:

Shaun Puckering, personal communication.