WORKS by Richmond River County Council have cut the likelihood of big fish kills at two sites on the Richmond.
The flood mitigation authority's floodplain project officer, Garry Owers said this week the works would enhance fish passage at Rocky Mouth Creek near Woodburn and at Empire Vale near South Ballina.
The Rocky Mouth Creek floodgates, built in the 1960s were first opened for tidal flushing in 1995 and were the site of the longest continuous flushing project in the State.
"The new works involve piping through a levee which also was built in the 1960s and effectively blocks fish passage in a section of the creek," Mr Owers said.
"Previously fish have become trapped and succumbed to deoxygenated water following summer floods.
"The pipe will allow fish to escape to the river ahead of the poor-quality water.
"A floodgate fitted to the new 1.2m pipe can be shut during a flood event to allow continued flood protection once fish have moved out."
Mr Owers said RRCC opened a temporary passage through the levee during the flood in February this year.
RRCC and landholders had been tidally flushing the Empire Vale creek through the Sneesbys Lane floodgates since 2000 but there was some fine tuning needed at the Empire Vale end.
"The problem arises when water pressure closes the floodgate at high tide and fish become trapped by deoxygenated water on the creek side of the floodgate.
"Two specially designed floodgates let fish, trapped by the low-dissolved-oxygen-level water, move through a sluice gate opened for their escape."
Some landholders had also shown interest in planting lomandra along sections of drain bank to filter out organic matter and nutrients and to stabilise banks.
"Keeping organic matter and nutrients out of the watercourse during summer will help prevent their rapid bacterial decomposition and the sudden drops in dissolved-oxygen levels."
The works are about three quarters complete and were paid for by a $62,500 grant from the Federal Government Biodiversity Fund, obtained through the Fisheries Research and Development Corporation.