Estuary entrance management

Information on estuary function and entrance management.

The Bega Valley Shire has 21 intermittently closed and open lakes and lagoons known as ICOLLs.

Waves, tidal activity and rainfall events shift sediments within estuary entrances, the build-up of sand from a combination of wave activity and lack of rainfall can lead to closures.

Sand incursion in Bega River following swell event.

Many of the estuaries within the Bega Valley are left to function naturally; however, there are seven estuaries where Council manually opens the entrance. This is done when water levels exceed predetermined trigger levels to prevent detrimental impacts on access, infrastructure or industry around waterways. These estuaries are Wallaga Lake, Cuttagee Lake, Bega River, Wallagoot Lake, Back Lake, Lake Curalo and Wonboyn Lake.

As per our Entrance Management Polices, estuary entrances are opened once water levels meet or exceed the specific trigger heights. Entrance management involves artificially removing sand around the entrance berm, to release built up waters to the sea. Generally, openings are conducted during the falling stage of the tide to ensure adequate head difference between the lake and the ocean for the first few hours of outflow however, timing of openings will give consideration to waves, ocean height and recent or forecast rainfall.

Wallagoot Lake opening 24th March 2021. — Wallagoot Lake opening 24 March 2021.

Entrance Management Trigger Heights for Bega Valley ICOLLS

Estuary	Trigger Height	Alternate Trigger*
Wallaga Lake	At or above 1.25m AHD	At or above 1.1m following a 3 month closure or 100m of rainfall forecast
Cuttagee Lake	At or above 1.8m AHD	n/a
Bega River	At or above 1.36m AHD	1.26-1.36 with 200m of rainfall forecast
Wallagoot Lake	At or above 1.4m AHD	At or above 1.2m AHD with 100m of rainfall forecast
Back Lake	At or above 1.4m AHD	1.2-1.4m with 100m of rain forecast
Lake Curalo	At or above 1.2m AHD	1m-1.2m AHD with 100m of rainfall forecast
Wonboyn Lake**	At or above 1m AHD	0.75-1m for minimum 2 months or 100m rainfall

*alternate trigger are applicable with forecast rainfall in the catchment and/or timeframe of closure. **staged entrance management policy.

Water level gauges have been installed in some of our estuaries which help guide openings and can be viewed at Manly Hydraulics Laboratory website

Council follows the NSW DPI fish habitat management policies and guidelines which support minimal interference. The long-term goal is to retain or progressively reinstate natural behaviour through progressive removal, relocation or modification of assets and activities that are impacted by inundation in order to raise trigger heights.

Are closed lakes still healthy?

Council receives many enquiries regarding estuary health with concerns over water quality, fish stocks and unpleasant smells and odour. Many closed ICOLLS retain good water quality with the flooding and drying natural components of the cycle which support ecological processes operating within the lake.

To find out more about ICOLLs check out the NSW Department of Planning, Industry and Environment Estuary entrance management webpage

‘Entrance Opening Policies’ for any Intermittently Closing and Opening Lakes or Lagoons (ICOLLs)

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02 6499 2222
council@begavalley.nsw.gov.au
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PO Box 492
Bega NSW 2550
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