Bullio cave was one of the first caves at Wombeyan to be discovered and explored by Europeans. It's also one of the best caves at Wombeyan, containing a wet and well-decorated streamway. The system catches water from the hillside to the northwest of the Wombeyan creek gorge, down through Bouverie cave and drains from Bullio into Mare's Forest Creek cave and finally to a resurgence in the gorge at Mare's Forest Creek. The streamway in Bullio is virtually perennial, with the cave only ceasing to flow during extreme drought conditions (2002 – 2003 was the most recent drought with conditions dry enough to cause the stream to dry up in the downstream area).
When SUSS began to resurvey the cave in 2001, we weren't expecting to be able to survey the whole stream because of the underwater section near the downstream rimstone dam. However, by the time we'd finished most of the cave, the sumped section was bone dry, not even muddy, so we've surveyed the entire extent of the streamway.
We also found a side passage off the streamway which was unknown to SUSS. Departing the stream on the southern side of the upstream passage, this route rises steeply to an extensive rockpile chamber with formation and calcified tree roots. The rockpile chamber turned out to be directly over the main stream canyon. When SUSS revisited the cave in 2007, there were many more tree roots in the chamber than in 2003.
During 2002, the intermediate levels of the cave including the Finger of Judgement were surveyed by SUSS, while the upper levels of the cave including both entrances and the pitch down from the upper entrance were surveyed in 2003. We also surveyed Mare's Forest Creek cave during 2002 – 2003 while the normal water was missing during the drought. A surface survey allowed us to position MFC cave relative to Bullio.
The final surveyed dimensions for W2/W65 Bullio cave were:
| Survey length: | 962m |
| Survey depth: | 58m |
| East-west extent: | 160m |
| North-south extent: | 119m |
The surveyed dimensions for W87 Mare's Forest Creek cave were:
| Survey length: | 216m |
| Survey depth: | 19m |
| East-west extent: | 64m |
| North-south extent: | 59m |
The gap between the downstream end of Bullio (at the lake, which may or may not be part of the active stream) and the upstream end of Mare's Forest Creek caves was measured as 30m. The gap between the downstream end of Bouverie and the upstream end of Bullio is estimated at 90m.
The stream in Bullio cave is 220m long, with another 100m of stream in Mare's Forest Creek Cave. It's the largest stream at Wombeyan outside the Figtree complex, and from the passage development it's been there for a long time. Dennis [in Caves and Karst of Wombeyan, 2004] considers the main stream passage to be an ancient course of Wombeyan Creek. The upper levels are parallel to the stream passage (see the silhouette) and presumably are a fossil level of the stream. The stream level is 40m below the upper level.
The Bouverie stream was dye traced to connect with Bullio cave by Julia James. Flow rate measurements also showed that Wombeyan Creek does not connect to the Bullio stream during flood. From the silhouette map, these results are surprising, given how close Bouverie cave is to Wombeyan Creek. There's also a surface gully which cuts across the gap between Bouverie and Bullio, joining with Wombeyan Creek downstream of Bouverie. The Bullio stream may not receive all of its flow from Bouverie. There is a substantial area of karst to the north west of Bouverie with no known stream cave, so there may be a separate system feeding into Bullio upstream of the known cave.
There is little prospect of discoveries in either Bullio or Mare's Forest Creek caves by dry cavers, but there is still a chance for the divers to extend the known cave at stream level. The downstream lake has been dived without a conclusive result. There hasn't been any attempt so far to dive upstream from Mare's Forest Creek cave. The upstream sump in Bullio was found to be tight and muddy. In drought conditions there may be more chance of diving upstream, and it's upstream where the prospects for extensions are best. The divers probably can't get to the end of Bouverie cave to dive downstream.
There were a total of 19 survey trips over three years to survey the two caves and the surface in between. We had a total of 13 surveyors contributing to the project; thanks! The surveyors were: Matt Fischer, Sean Hill, Geoff McDonnell, Phil Maynard, Kevin Moore, Verity Morris, Rod O'Brien, Martin Pfeil, Richard Pfeil, Alan Pryke, Megan Pryke, Jodie Rutledge and Mark Staraj. Additionally, Alan Pryke led a photography trip to document the main stream in Bullio and the ladder pitch. We can't do these projects without people volunteering massive amounts of time and energy; just as well it's good fun.
The upstream sump of the Bullio stream receives water from Bouverie cave, W3 (see the silhouette map). Following downstream from there, the stream passes through breakdown and joins a fossil side branch which contains gours. Leaving the breakdown area, the stream becomes a high canyon with extensive decorations in the roof. There is a side passage which leads to a collapse chamber lying above the stream passage. This contains formation and tree roots. The stream passes under a major flowstone blockage and then meets the passages down from the upper level of the cave. Just near the junction, the stream diverts through a passage which is normally sumped and reappears as a lake downstream from the junction. This is held behind an impressive rimstone dam. Immediately downstream of the dam, the stream disappears into an impenetrable sump. The main passage continues another 30m to a lake which presumably receives water from the stream. This is the end of the known streamway.
From the lake, there is a gap of 30m to the upstream sump of Mare's Forest Creek cave, W87. The passage in W87 is more phreatic and less canyon-like than Bullio, with occasional formation above the waterline. This cave normally contains an extensive lake, but was dry with a muddy floor when SUSS surveyed it. There are several entrances out to the gorge, and the lowest of these is a resurgence when there is water in the cave.
Ascending from the junction with the Bullio stream, the normal way up to the entrance is a flowstone slope which leads to a short ladder in a vertical squeeze. This climbs to the intermediate level of the cave, which is a fossil level of the stream and contains extensive decoration. The alternative way up from the stream climbs out of a canyon into a room with a very impressive stalagmite named the Finger of Judgement. From there, a series of flowstone climbs leads to the intermediate level. From the intermediate level, a 12m near-vertical ladder leads to the upper level of the cave.
At the top of the ladder, a slope leads up to the well-decorated route out of the cave. This is a series of chambers, connected by tight passage. The upper entrance is a side-route leading up to an 8m pitch. The entrance is a 1m diameter hole in a horizontal stretch of bare rock on the hillside. On the main route out, there is a 4m climb down a soil bank in the largest chamber, followed by a series of climbs up to the main entrance. The entrance is 5m high by 3m wide, in a doline above the gorge.
The best way to do the cave is to abseil the upper entrance (8m pitch), then pull down the rope and use it to rig the main ladder. Abseil the ladder with a rebelay off the top rung. To ascend the ladder, self-belay up the rope and climb the rungs rather than trying to SRT up the rope. Use a tape or the rope as a hand line down the soil bank and exit out the W2 entrance.
The gear required to rig the cave this way is a 30m rope, a long tape for the upper entrance (rig off a tree), three rigging tapes and karabiners for the ladder pitch and possibly another tape for the soil bank. The stream is cold; consider bringing a wetsuit for the upstream passage. The stream is mostly waist-deep or less, but there is a swimming section upstream of the side passage. Downstream, it's possible to bridge over the pool to the rimstone dam (maybe not possible for short people).
