Making The Entrance channel ‘flood ready’

With the end of the busy Summer holiday period, and the departure of migratory Little Terns from the Karagi sand spit, Central Coast Council is set to commence the next stage of works this month at The Entrance channel to ensure it is in an appropriate “flood ready” state, by establishing a pilot channel.

Council currently monitors the channel condition in real time (via remote cameras, satellite imagery and gauges, that monitor tidal range within the estuary) and forecasts catchment inflows and lake heights.

This allows early intervention at The Entrance channel if a flood event is expected.

Council’s Unit Manager Environmental Management Luke Sulkowski said the foreshores of Tuggerah Lakes, however, would always be flood prone, regardless of the channel configuration.

“While currently we have not reached any of our established triggers requiring Council to undertake work on The Entrance channel, we plan to excavate sand from the lake side of the sand berm and to the north of the rock shelf as a pre-emptive action, given the forecast shift to La niña weather conditions,” he said.

“This is in accordance with our procedures to reduce the time and effort required by Council work crews in the event of a flood and to ensure appropriate response actions are implemented faster for our community.”

Council’s main concerns with the current configuration of the channel are with its tendency to track south between the rock shelf and The Entrance Beach groyne.

“This is an observation we have continued to see since construction of the groyne in 2017,” Sulkowski said.

“Prior to the construction of the groyne, even when constricted, the channel generally tended to flow to the north of the rock shelf.

“With the channel tracking this far south, we have seen continued erosion to the southern foreshore of the channel and impacts to infrastructure including beach access points and The Entrance channel lifeguard tower.

“In this configuration the channel’s capacity to naturally widen and scour during flood is limited.”

Council understands the NSW Government, which constructed the groyne in late 2017, is currently reviewing its impacts.

“In the interim, from February 20, Council expects to spend about three days on site establishing a pilot channel to the north of the rock shelf,” Sulkowski said.

The pilot channel will be 40-50m wide, and at a depth slightly above the current lake height.

To slow infilling due to natural processes, such as tides and wave run-up, and extend its usefulness, it will not be connected through to the ocean.

Whilst on site, remaining items that were installed to assist with the Little Tern breeding will also be removed.

“If a flood event occurs, and intervention triggers are activated, Council will then be able to connect the pilot channel to the ocean as lake levels rise and when there is sufficient hydraulic energy to establish flow,” Sulkowski said.

“It is important to understand that unlike our other coastal lagoons, the Tuggerah Lakes are very low, almost at sea level, and if a connected pilot channel were to be constructed now, it would not flow but instead result in almost immediate infilling with sand from the ocean due to dominant coastal processes.”

Sulkowski said that given the dynamic nature of the coastline and The Entrance channel, if it became apparent during the works program, there might be a need to make some modifications to the proposed program in order to ensure the most appropriate outcomes were achieved.

The planned works will be funded by Council as a flood preparedness measure, noting that the works are ineligible for funding under the NSW Government Boating Access Program.

Sulkowski said although at times heavily constricted, the entrance to Tuggerah Lakes has not closed for more than 30 years.

“Restriction at The Entrance channel is a natural process, and benefits the health of the estuary,” he said.

“The marginally higher lake levels that are retained during dry weather events allow for fringeing wetland habitats to be inundated, and for better mixing to occur between the central lake basin and those areas closer to shore.

“This results in reduced wrack, algae and pollution impacts.”

Council Administrator Rik Hart said Council was acutely aware of the need to monitor the channel, hence Council’s investment in the technology used 24/7 to gauge tidal ranges.

“The planned works this month are a part of this proactive management of the channel,” he said.

“However, Council encourages foreshore residents to be flood ready by understanding their local flood risk, planning for what to do if a flood occurs, getting their property ready, staying informed and looking out for each other.”

The works at The Entrance channel will commence on Tuesday, February 20 and be undertaken over a three-day period.

The news was welcomed by Member for The Entrance David Mehan, who has been agitating for action o the channel for some time.

“The Entrance Channel is currently heavily constricted and the sand berm across the channel mouth is larger than that which existed at the time of the 2020 flood,” he said.

“Council will now excavate a pilot channel to ensure that if a flood develops it can break out instead of ponding behind the sand berm.

“In welcoming these works, I note my concern that Council still lacks the will and the necessary procedures in place to maintain the channel in a flood ready condition and I’ll continue to do all I can to ensure this occurs.”