Lake Eildon Project

In Real Conditions - Planning Pays

Earlier this year Descend Underwater Training Centre won a deep construction project in Lake Eildon for Goulburn Murray Water.

The Project involved the removal of old trash screens on the low level water outlet and the installation of new screens. Now that sounds pretty straight forward until you consider that the water temperature is 8 Deg. C. The Visibility less than one metre, the depth about 30 metres, all the dives must be conducted from either boats or barges and regulations require a decompression chamber be on site. All of this coupled with the owners requirements for access to the water flow mean a very small window of opportunity. The fact that no accurate plans were available of the existing structure meant comprehensive planning was required.

The planning started with a video survey and measurements of the existing outlet. From this new stainless steel trash screens and bulkheads were designed and manufactured. The screens were delivered to the Descend base in Albury where Descend staff built a timber mock up of the concrete structure that the new screens had to fit. The idea was to test fit the screens in as realistic conditions as possible to find out what the problems were. Imagine the odd looks when visitors to neighboring businesses drove into the car park one winters evening to find a dive team, kitted up in helmets and complete with dive boat, in the middle of the car park in the dark fitting screens and bulkheads to a wooden box!

The "dry dive" was certainly worthwhile and several problems were found and solutions developed to ensure the job ran smoothly. At the same time the complete job was choreographed in minute detail.

The total number of dives required was worked out in advance and each dive numbered. Each diver knew in advance which dive he was to do. And at what depth and for how long. Each diver was briefed on exactly what he had to achieve and how to go about the task. The planning was completed. Now for the actual work.

The Descend work boat, fitted with half tonne winch and the customers two barges were used for the work platforms. These were loaded with the hydraulic power pacs, hydraulic tools, video surveillance systems, hot water generator and hot water suits (a luxury usually reserved for off shore divers) and of course all the standard diving equipment, compressors, panels and umbilicals. The recompression chamber was located on the shore adjacent to the job and within 5 minutes travel time from the dive control position.

The divers commenced with nondestructive testing of the concrete structure using explosive power tools and known charges. This was followed by the removal of the old screens using an hydraulic cut off saw. Then the fitting of the new screens which we had already fitted in the dry. All work was monitored using the video system and we had contingency plans in place for any situation. We were right. As they say "Murphy is alive and well", and he certainly came to visit us during those five days! The concrete block was a different size to the drawings, which resulted in modification being made to the assembly. The faces of the block were not flat and special grouts had to be used to seal the plates to the block and when it was finally fitted, the bulkheads did not seal and more changes had to be made. Luckily all of our solutions worked.

All in all it went quite smoothly, and the end result was better than expected. The project was completed in the allowed time, and "under budget," the Supervising Engineers favourite terms, and again proving that proper planning pays and prevents poor performance.

DIVE Log Australasia, January 2000 - Page 25