After discussions with Wayne on the different options available, we settled on using a combination of a high resolution scanning sonar (Kongsberg MS1000), and a small, lightweight ROV for further exploration. The original borehole was only 90mm in diameter, therefore it had to be increased to allow the equipment through the hole and into the coal tunnels.
The data from the MS1000 sonar allowed us to determine the best location for additional boreholes to allow the deployment of the sonar for further mapping of the flooded coal mine.
Thanks to Wayne Griffioen and Emily Bartlett from Tasman Geotechnics, as well as Simon Hills from Imbros for making this project run extremely smoothly despite the horizontal hail and extremely cold conditions on the day. We look forward to continuing the exploration of the coal mine once the additional boreholes have been drilled.