Aquatic scientists complete first round of surveys for dam raising
06 December 2018
Environmental flow regime to be recommended
A Council consultant has completed the first round of field surveys required to recommend an environmental flow regime from Clarrie Hall Dam that will minimise any impact of the raising of the dam wall on the downstream ecology while maintaining water security for the Tweed Shire.
Scientists from Eco Logical have undertaken two field trips to the Tweed to study 18 kilometres of waterways in the Doon Doon Creek and Tweed River down to Bray Park Weir to assess likely impacts of the raising of the dam on water quality and aquatic habitat.
The most recent surveys were undertaken before and after a planned release from the dam.
Releases from the dam occur during times of low flow to ensure the continued health of the waterways or, occasionally, to assist to hold back a saltwater high tide from overtopping the Bray Park Weir pool.
The scientists observed a higher diversity of aquatic fauna after the planned release than before, with Cox’s gudgeon, hardyhead, long-finned eel and macrobrachium shrimp added to their sightings.
All up, nine fish species were found in the waterways, namely bass, catfish, firetail gudgeon, mullet, rainbow fish, smelt, striped gudgeon, Cox’s gudgeon, hardyhead, turtles, eels, crayfish and shrimp.
The scientists also observed frog species before and after the release, sighting the same species but more frog numbers after the release.
The dominant three frog species along the waterway are the tusked frog, eastern dwarf tree frog and Peron’s tree frog.
On the Tweed River, multiple eastern stony creek frogs and one red tree frog were sighted.
On Doon Doon Creek, one cane toad and one eastern stony creek frog were observed.
The scientists have installed loggers along the waterways 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 due to stratification during low flow periods.
From the field data collected so far and additional surveys in the new year, Eco Logical will recommend an environmental flow regime from the dam to minimise any impact of the raising of dam wall on the downstream ecology while maintaining water security for the shire.
The Eco Logical assessment reports and methodology can be found in the Document Library at https://www.yoursaytweed.com.au/clarriehalldam.