I'm writing this as a warning to anyone considering freediving the Swildon's sumps, but may not have really appreciated the risks involved. On previous trips to Swildon's 4 and 9, myself and others had exercised great caution regarding Sumps 2, 3 and 4 and used to be concerned that we would find them silty/impassable (especially in dry weather). All of these previous trips, however, we had found each sump roomy and pleasant, and gradually convinced ourselves that the stories we had heard of cavers bailing out silt mid-dive was exaggerated, or for some reason no danger to us.
After two days of dry weather after Storm Claudia, a small group including myself decided to do a trip through the first few sumps. A few weeks ago the water levels had been extremely low, and now unsurprisingly the cave was a gushing river of whitewater. Sump 1 was no longer a duck but a deep scummy pool, and I noticed it felt slightly tighter than it had ever felt before (I'm on the thin side), requiring a good few hard tugs on the line to get through to Swildon's 2. This should have been the first warning sign that we would encounter problems in later sumps - the fact that we'd only ever worried about silt because of dry conditions mistakenly lead me to dismiss this.
With a mask and hood on, I lay in the Sump 2 pool and took a deep breath in. The visibility was poor, but the sump seemed as wide and roomy as it had always felt before. About 7 metres into the sump, I encounter the lowered ceiling, meaning I was close to the airbell. However, it was at this same point I noticed the floor level rising due to a large sediment deposit. I soon find my chest wedged between the ceiling and the floor - hard tugs on the line get me no further through the sump. I put my hand in front of me and feel the rope running through a gap only a few inches wide, with the floor a thick sediment bed - the visibility turned from poor to none. At this point I decide that to try and push through would be suicidal - even more so considering that the high water levels means that there may not be air for another several metres after the constriction. I managed to use the line to manoeuvre backwards out of the constriction, until I was free enough to flip my hands around on the line and attempt to reverse the significant distance I had covered so far. A mistake whilst performing this, or a delay in deciding to, could have had fatal consequences. Emerging back out of the upstream end, I was panting and significantly more out of breath than I had ever found myself from Sump 3. We turned around and made a prompt exit, losing only a glove.
Before the trip, myself and my peers had lead ourselves into a false security of thinking we understood how weather events correspond to the hydrology of the cave. We did not understand this then, nor do we now, and should have recognised that neither dry nor wet weather is a simple guarantee of the sumps being passable or impassable. I suppose that the gushing water through the cave picked up more sediment than usual from higher levels - when this sediment reaches the later sumps, where the pools are larger, the velocity of the flow decreases and leads to increased deposition. The lowering of the ceiling in Sump 2 limits the flow of water further, maximising deposition, which is potentially why I only encountered significant silting at that point. This is not to say that to dive these sumps in other (or even any) conditions would be safe, nor that this theory is correct.
I cannot offer any comforting advice to anyone who wishes to freedive sumps, but would urge you to consider whether you would dive into one knowing that you may have to turn around at the very end, or find yourself stuck in a constriction you could not navigate?
After two days of dry weather after Storm Claudia, a small group including myself decided to do a trip through the first few sumps. A few weeks ago the water levels had been extremely low, and now unsurprisingly the cave was a gushing river of whitewater. Sump 1 was no longer a duck but a deep scummy pool, and I noticed it felt slightly tighter than it had ever felt before (I'm on the thin side), requiring a good few hard tugs on the line to get through to Swildon's 2. This should have been the first warning sign that we would encounter problems in later sumps - the fact that we'd only ever worried about silt because of dry conditions mistakenly lead me to dismiss this.
With a mask and hood on, I lay in the Sump 2 pool and took a deep breath in. The visibility was poor, but the sump seemed as wide and roomy as it had always felt before. About 7 metres into the sump, I encounter the lowered ceiling, meaning I was close to the airbell. However, it was at this same point I noticed the floor level rising due to a large sediment deposit. I soon find my chest wedged between the ceiling and the floor - hard tugs on the line get me no further through the sump. I put my hand in front of me and feel the rope running through a gap only a few inches wide, with the floor a thick sediment bed - the visibility turned from poor to none. At this point I decide that to try and push through would be suicidal - even more so considering that the high water levels means that there may not be air for another several metres after the constriction. I managed to use the line to manoeuvre backwards out of the constriction, until I was free enough to flip my hands around on the line and attempt to reverse the significant distance I had covered so far. A mistake whilst performing this, or a delay in deciding to, could have had fatal consequences. Emerging back out of the upstream end, I was panting and significantly more out of breath than I had ever found myself from Sump 3. We turned around and made a prompt exit, losing only a glove.
Before the trip, myself and my peers had lead ourselves into a false security of thinking we understood how weather events correspond to the hydrology of the cave. We did not understand this then, nor do we now, and should have recognised that neither dry nor wet weather is a simple guarantee of the sumps being passable or impassable. I suppose that the gushing water through the cave picked up more sediment than usual from higher levels - when this sediment reaches the later sumps, where the pools are larger, the velocity of the flow decreases and leads to increased deposition. The lowering of the ceiling in Sump 2 limits the flow of water further, maximising deposition, which is potentially why I only encountered significant silting at that point. This is not to say that to dive these sumps in other (or even any) conditions would be safe, nor that this theory is correct.
I cannot offer any comforting advice to anyone who wishes to freedive sumps, but would urge you to consider whether you would dive into one knowing that you may have to turn around at the very end, or find yourself stuck in a constriction you could not navigate?
