The ins and outs of the Shire's ICOLLs

28 August 2020

There’s much to like about this shire of ours: the people, the stunning landscape, the coastal wilderness and historic townships dotted here and there.

But what about the ICOLLs? The what?

The Irresistible Collection of Lovely Landmarks?

Not quite, although ICOLLs are responsible for the presence of many much-loved coastal landscapes within the Shire.

ICOLLs are intermittently closed and open lakes and lagoons, and we have more of them in the Bega Valley Shire than anywhere else in NSW.

The Bega Valley Shire has 24 of the 70 ICOLLs found in NSW, and they are a product of wild oceans and not-so-wild river systems.

Council’s Coastal Management Officer, Rachel Duczynski said ICOLLs are a natural part of our environment being shaped by opposing catchment and ocean forces.

“ICOLLs occur where catchments are generally smaller in size, receive lower catchment inflows and are wave dominated,” she said.

“ICOLLs close when ocean waves and tides push sand into the entrance which, without further freshwater flows into the estuary from the catchment, gradually closes the channel.

“Closed estuaries often cause community concern over perceived ‘poor’ water quality, odours and varying water levels, however, these systems rely on the flooding and drying cycles to support ecological communities and can retain good water quality over extended periods of closure.

“We get lots of questions about our estuaries and entrance management, and with the recent high rainfall, this a great time to explain some of the facts.

“We currently manage six of the Shire’s 24 ICOLLs, each with their own triggers for opening, based on inundation of key public and private assets.

“The rain we’ve had over the last few weeks has led to many of our estuaries opening to the ocean either manually through Council intervention, or naturally.

“Throughout July, Council opened entrances of the Bega River, Back Lake, Wallaga Lake and Lake Curalo as trigger heights were reached. Natural openings occurred at Cuttagee Lake, Murrah River, Bournda Lagoon and Bunga Lagoon.

“The strong water flow during this period has helped achieve deeper channels and wider entrances in the case of our manual openings.

“A large volume of water within the ICOLL will wash more sand from the entrance, increasing potential of a longer lasting opening.

“The trigger heights we use aim to strike a balance between allowing ICOLLs to mimic natural processes, while reducing the potential for inundation of private and public assets.

“It is important to note, however, that the length of time estuaries remain open depends on the volume of water flowing from the catchment, tidal movement, and the influence of wave activity at the entrance.

“Even with increased channel depth and width, ICOLLs are constantly changing, sometimes closing soon after opening, and it is common for them to remain closed for several years at a time.

“Bega River was last opened in February 2020 and closed in early June due to lack of ongoing rainfall and multiple large swells.

“Three successive years of below average rainfall have resulted in the Wallaga, Cuttagee and Curalo entrances opening for the first time since 2016, so the community is happy to see these estuaries open again.

“ICOLLs will continue to shape and reshape our coastline, and even with the challenges they present, it’s worth remembering that ICOLLs create many of the natural landscapes that our Shire is renowned for.

“They are a fascinating and natural part of our coastal environment, and as with many natural occurrences, they can be positive and problematic,” Ms Duczynski said.

To learn more about the Shire’s ICOLLs, visit our Entrance Management Policies page.