July 24, 2023

The recently completed Karaaf Wetlands Estuary Mouth Assessment has found that opening the Thompson Creek estuary does not flush more stormwater out of the wetland, increase the salinity of the local groundwater system, nor alter the interaction between the stormwater inflows and the claypan areas at the westerly end of the wetland.

Overall, the review concluded that opening the estuary will not mitigate the effects of increased stormwater inflows on the Karaaf wetlands to the west of Point Impossible Road.

Corangamite CMA’s Estuaries and Environmental Water Manager Jayden Wooley said: “Most estuaries in the Corangamite catchment are intermittently open/closed estuaries, which close from time to time as part of a natural process. Maintaining this natural intermittence is vital to support the estuarine ecosystems, including the protection of the unique plants and animals that thrive in these systems.” 

“Because of this, artificial estuary openings are minimised in the Corangamite region as there is generally no environmental benefit, and artificial openings can put ecological values at risk. This approach has historically been strongly supported by research and the findings of this study further support this,” Mr Woolley said.

“Artificially opening an estuary only occurs when water levels start to impact on built infrastructure, including roads and buildings, or inundation of agricultural and residential land,” Mr Woolley concluded.

In September 2022, Surf Coast Shire Council completed the Environmental Assessment Karaaf Wetlands Report to determine the current extent and quality of existing vegetation and identify the impacts of stormwater flows from the western outlets connected to residential development.

One of the key findings in the potential strategic responses to factors leading to the death of saltmarsh shrubs in the vegetation report was: “if stormwater inputs into the wetlands can be prevented or at least substantially reduced, the development of thresholds for subsequent decision-making around artificially opening the Thompson Creek entrance could be a useful tool for minimizing the extent of future dieback events. In the interim, it is recommended that the estuary be maintained in open condition to assist recovery of the impacted saltmarsh vegetation.”

The purpose of the recently completed Karaaf Wetlands Estuary Mouth Assessment was to see if opening the estuary would improve flushing of the wetland to the west of Point Impossible Road and assist recovery of the impacted saltmarsh vegetation.

Surf Coast Shire Council General Manager Placemaking and Environment Chris Pike said: “The Karaaf Wetlands Estuary Mouth Assessment provides all agencies involved in the protection of the Karaaf Wetlands with valuable information. It is part of the further work we identified was required following the environmental assessment commissioned last year.

“It provides us all with another key piece of data which will greatly assist with Council’s work in developing effective short and long-term options to reduce the volume of stormwater entering the Karaaf Wetlands.”

The focus questions for this investigation were:

  1. Could opening the estuary allow more saline water mixing, thereby increasing salinity in the areas of saltmarsh impacted by freshwater from stormwater inflows?
  2. Could opening the estuary allow stormwater to be more readily flushed out of the wetland and thereby increase the salinity in the saltmarsh most impacted by freshwater flows?

The full report can be found here: Corangamite CMA Knowledge Base - Karaaf Wetlands Estuary Mouth Assessment (2023) (

More information on the Corangamite CMA’s estuaries can be found here:


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