Trip Report - Tronoh Lake Dredge Hole - May 2010

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The team travelled to Harrietville in Northern Victoria to research the depth and visibility of the Tronoh Dredge Lake. Harrietville is a simply stunning part of Victoria steeped in gold mining tradition dating back to the 1800's. The Tronah dredge was the largest gold dredge of its kind in the world and was shipped to Malaya in 1956. The hole that it left has since filled with water and was the setting for this adventure. We had heard that the depth was anywhere from 12 to 140 metres. Internet research suggested it was not more than 40m as the dredge could only dig to a depth of 41m. In May 2010 we decided to find out for ourselves. We left Melbourne at 7.30pm on Friday night and made our way up the Hume Highway to towards Harrietville. We arrived at 11.30pm and checked into the accommodation. The next morning Steve, Rich, Jase and Mischa were presented with the biggest cooked breakfast we had ever seen. You could feed an army with that! With full bellies, we made our way some 5 minutes to the dive site. We had two video rigs set up to capture the underwater environment. Mischa was having troubles with his ears, so provided the team support from the surface. Steve, Rich and Jase geared up to get ready for the dive. We had a steady stream of onlookers who were very inquisitive as to what we may find in there and how deep it was. The plan was to do an initial check out dive to determine the deepest point and then a second dive to circumnavigate the site and determine what the bottom topology was like.

Dive One

As soon as we got into the water, we could see that the visibility wasn't great. It would have been around 2 metres for the first 5 metres of depth. As we descended further, we felt a distinct thermocline at around 10 metres and the visibility dropped to 1 metre at best. The water was a distinct green colour, most likely from algae bloom and the water temperature was 13 degrees Celsius. At 14 metres, we found the bottom and continued on a compass bearing of NE to the deeper part of the lake. The deeper part of the lake ended up only being 17 metres. The dive was thumbed and we ascended to the surface to discuss what we had found. The team were a little surprised and dissappointed by the visibility and depth findings. It was decided that Steve would take the video gear back and Rich and Jase would do the second planned circumnavigation dive to determine if we had missed the deeper part and what the bottom topology was like.

Dive Two

Rich and Jase descended again and had to keep in touch contact to be able to determine where each other was. Their 21-watt HID lights looked like green light sabres and the guys had to stay around 300mm from the bottom at all times. They scanned the lake floor and determined that there was a thick loose silt layer that wobbled when they waved the water column above it. No fish life were visible, about all that they saw was an old kids bike embedded deep in the silt and a pair of kids swim goggles near the pontoon. Their maximum depth was 17.2 metres and their dive time was around 40 minutes.

Conclusion

It was a nice drive to a lovely part of Victoria with some rich history and some beautiful scenery. We were a little disappointed in the visibility and not finding the deeper section. We may need to return during the middle of winter and try to find the elusive reported 40 metres depth in hopefully better visibility.



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