Scientists map creek and river habitat for dam raising
Thursday 28 June,
2018
Council consultants have completed the first survey of Doon Doon Creek and the Tweed River down to Bray Park Weir to determine how a raised Clarrie Hall Dam may affect fish and other aquatic species.
The scientists from Eco Logical last week studied 18 kilometres of waterway, noting habitat features of the river and the location of pools, riffles (rocky or shallow parts with rough water) and rapids.
They took 640 depth-readings and found depths ranging from just a few centimetres to one pool 10 metres deep in the river.
During the survey they sighted Australian bass, freshwater catfish and schools of freshwater mullet.
The scientists will return to the Tweed in spring and summer to look for fish, frogs and other aquatic creatures at six sites identified in last week's survey. To do this, they will rely on both visual sightings and nets.
They also will install loggers to monitor the dissolved oxygen content and temperature in the water, and any changes to them over the seasons. This will inform Council of any layers within the deep pools, which are low in oxygen or colder …. (and the why behind it).
The scientists will return to monitor the waterways during a release from Clarrie Hall Dam, if and when one is required. Releases occur during times of low flow to ensure the continued health of the waterway or, occasionally, to assist to hold back a saltwater high tide from overtopping the Bray Park Weir pool.
From the field data collected, Eco Logical will recommend an environmental flow regime from the dam that will minimise any impact of the raising of dam wall on the downstream ecology while maintaining water security for the Tweed Shire.
