|Travelling Australia - Journal 2014
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Balranald - Deelder Fish Lock
|Deelder Fish Lock is the concrete structure on the left of the low level weir at Balranald.|
|The Deelder Fish Lock
The life cycles of at least 36 species of native fish include migration along rivers and migrations of up to 1400 kilometres have been recorded. But over many decades a succession of "river-taming" projects has installed weirs, dams and barrages impeding water flow and making migration up or downstream difficult to impossible.
More than 70 "fish-ladders" or "fishways" have been installed in New South Wales in an attempt to provide realistic migration paths for fish and to restore the dwindling numbers of native fish left in Australian rivers by facilitating natural increase.
|Balranald visit - page 2|
Most designs originated in Europe for strong-swimming fish such as trout and the realisation has belatedly dawned that Australian fish are mostly not such strong swimmers and conventional fish-ladders were not nearly as successful as had been hoped.
The Deelder Fish Lock installed on the low level weir across the Murrumbidgee River at Balranald in 2002 takes a different approach to helping fish get past weirs. This equipment operates in a similar manner to locks for shipping but deals with fish and other water-living creatures.
When installed the lock was manually operated but it has since been automated.
The lock has a long chamber below water level with gates at each end and one gate in the middle. The lock operates in four phases:
1. Attraction Phase. The entrance gate at the downstream end of the lock is opened fully, the exit gate at the upstream end is opened enough to allow a pre-determined current to flow through the lock and out of the entrance; this flow attracts fish trying to get upstream and swimming against the current.
2. Filling Phase. The entrance gate closes (after one to two hours) and the lock fills with water.
3. Exit. The exit gate on the upstream side open and fish are free to swim out at the higher level. The downstream gate is slightly opened so current flows in through the exit and encourages fish to leave.
4.Translation.The lock returns to the Attraction Phase condition.
During trials in 2003 fish were netted at entrance and exit to determine how well the fish lock worked. Most native species present passed through the lock as intended, but at least two species would not pass through. Results overall were encouraging, whether we will see more Deelder fish locks remains to be seen.