Intermittently closed and open lakes and lagoons (ICOLLs) are estuaries with entrance channels that naturally become blocked by a build-up of sand, then open again when water levels become high enough to overtop this barrier.
Waves and incoming tides move sediments into estuary entrances, and outgoing tides and water movements shift sediment out. The frequency and duration of entrance opening varies considerably across ICOLLs, which have adapted to these variations, including changes in water chemistry such as salinity.
When entrances close, water levels can increase from rainfall, run-off and wave overtopping. This can cause inundation of low-lying foreshore areas, including urban areas.
Local councils artificially open ICOLLs to manage inundation of private and public infrastructure. However, opening ICOLL entrances comes at a cost and must be weighed against real or perceived benefits of intervention. For example, entrance manipulation can cause unintended negative impacts to water quality, the physical form and natural functioning of these systems.
Alternatives to artificially opening entrances include relocating, modifying or raising at-risk low-lying assets.
We work to minimise impacts on sensitive ICOLL environments, and protect and improve the health of estuaries.
To achieve this we support councils by:
- providing technical and financial support to develop coastal management programs (CMPs) for estuaries, including ICOLL entrance management plans
- supporting the relocation and/or raising of assets and low-lying land through the Floodplain Management Program
- working to monitor, evaluate and report on the condition and physical properties of estuaries, which helps in the development of CMPs
- providing a structured approach to help manage the impacts of land-use activities on waterway health with the Risk-based Framework for Considering Waterway Health Outcomes
- developing water quality and river flow objectives based on community values and uses of waterways across our coastal catchments
- providing technical and funding support through our Coastal and Estuaries Grants Program for estuary management projects, to manage risks from coastal hazards, restore coastal habitats and improve estuary health.