Rock Bottom at Waikaremoana
National Film Unit, 1950
Beautiful lake Waikaremoana was once the head of a great gorge .
Between 10,000 and 25,000 years ago, rain recon structure faulted and a colossal landslide occurred which piled up against what is now called Rahui bluff to form a natural dam twelve hundred feet high. The tumbled nature of the upended strata caused leaks in the bottom of the lake which found their outlet in the surrounding country. These leaks formerly fed the hydro-electric stations at Tuai and Piripaua but today water is piped from the lake and the leaks are sheer waste. The waters of Waikaremoana fall steadily and engineers have decided to stop the leakage at its source.
Divers are now engaged locating and reporting on the filling of the leaks on the lake bed .
This operation is unique in the annals of hydro-electric works and it's hoped that valuable power will be conserved Divers at Waikaremoana make the descent on a stage which drops them 30 feet to the waters edge. Special equipment is being pioneered by the National Film Unit for movie work underwater this cameraman is going to follow actual diving operations and will shoot film at depths of 15 to 60 feet. This is believed to be the first time that a full-sized movie camera has been incorporated in a diving helmet. He's ready for the stage now . The attendant of the air panel is on the phone and talks to the diver already in the water. Owing to the great weight of the special helmet it's necessary to string him up whilst dressing for the descent is completed . Fitting of the gear demands care and attention as it's too late to make alterations when underwater. Camera controls are tested to ensure free movement. All okay! on with the side glass. The attendant is conversing with both divers now In our cameraman's case the business of getting underwater is complicated by additional weight, and the difficulty of keeping balance this is a very real hazard, until such time as the air inside the helmet creates buoyancy.
Although, we find walking a bit difficult it's a relief at last to be under the strains gone from the shoulders . We move out forward and keep our eyes peeled for the diver He's pulling out, ready for travel wants plenty of slack so there'll be no drag on him. He depresses the air outlet valve and stops his ear supplied to reduce noise while he gets the okay to move. Time for us to get going.
The terrain is ragged as the surrounding country. Flat shelves of rocks as big as houses give way to crags, precipices and crevasses of at depths which seem to be bottomless. This soft mud bottoms are a lot easier to move over than the rocks. There's the diver using a movement which gives speed over distance. There's less resistance to water this way We soon reach our first leak. Holes like this are the gateway to the honeycomb of passages under the lake bed. They contain an estimated 80,000 cubic yards of volume. They spill water wastage and must be filled in .
The divers decided it's necessary to buoy the site of this lake . These buoys are visible on the surface and mark out the area of filling operations so that a barge can be correctly positioned above for dumping spoil into the hole. Sometimes rock formations drop the effective filling of a leak they must be blasted away with high explosive. Pneumatic drills are used to make the shot holes. [Drilling sounds] The rock is not very hard and will shatter easily. A waterproof fuse and a lanolin sealed explosive charge are used . Pressure waves are magnified underwater and owing to the concussive effect the diver must move well out of range while the charge is fired from the shore. On shore tons and tons of spoil are loaded into the barge by crane. In filling a leak, large rocks are first dropped followed by smaller metal, sand and finally clay. The barge has no motive power of its own but can be maneuvered to any part of the bay by horses which are attached to winches. The load is dropped through doors in the bottom . As we wait near the leakage area we see the bottom of the barge loom over us.
What will the dumping look like underwater we wonder. It's away! we can see no actual metal falling owing to the millions of the air bubbles bursting in the water as tons of spoil rush to the bottom . Above us the shadowy outline of the barge move forward on its way for another load as the water clears we see the metals done a good job. Timber is jammed into the mouths of many leaks and before they can be filled they must be cleared so that the dumped spoil will have unobstructed entry into the hole. The diver is about to attach a steel hoses to the bowl of the sunken tree so the crane is sure we will be able to haul it out of the way. Thousands of tons have been removed this way. It's time for us to come out . We've been down two hours around the 60-foot mark. We must observe our time and exercise., both at the 20 foot 10 foot levels. While we wait there to decompress all nitrogen formation caused by pressure must be forced out of our bloodstream as a precaution against the dreaded bends.
Man's invasion of an age-old natural system of water control by sealing the lakebed has resulted in 45% of leakage being arrested but man will never be satisfied until he has all available water under his control to be harnessed as he wills to generate sufficient electric power for the factories and homes of New Zealand.
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