Estuary opening at Narrawong
High swells building an unusually large sand beach berm has led to the CMA and Parks Victoria taking proactive action to support the Surry River at Narrawong with an authorised artificial river mouth opening (ARMO) on Friday, February 10.
The decision comes following an extremely large and unseasonal 8m swell hitting our coastline last week, depositing large volumes of sand at the estuary mouth and inputting significant volumes of seawater into the estuary.
Past monitoring and research by the CMA have indicated that such seawater intrusions, which typically occur during autumn and early winter, can result in dissolved oxygen depletion in the estuary, leading to vegetation dieback and risk of fish death events.
Artificial openings are not the preferred management approach, with the management authority preferring to let the mouth of the river open and close naturally.
However, ARMOs will be undertaken after significant assessment, usually when there are sufficient dissolved oxygen levels in the estuary.
Opening an estuary can only be completed by authorities when conditions are safe and appropriate. Opening of an estuary mouth without authority can lead to heavy fines and prosecution.
In this instance, however, due to significant rainfall and streamflow during spring and early summer 2022, the estuary was highly oxygenated, which allowed for a safe and appropriate artificial opening.
The beach berm covering the mouth is also higher than has been seen in a number of years at this stage of summer.
Therefore, we are the opening estuary to reduce the foreseeable negative impacts on the system, including prolonged inundation of adjacent public and private land, native vegetation dieback and fish death risk, often encountered during late autumn and early spring.”
The opening aimed to lower the estuary water level, reduce seawater loads within the estuary and lower the height of the sandbar at the estuary mouth. The opening will not be permanent, and the system is expected to close naturally without rainfall.
The decision to attempt an ARMO is being made in the best interests of the long-term health of the estuary.
Information on how estuaries open and close can be found here: https://www.ghcma.vic.gov.au/what-we-do/estuary-management/