Maroochy River Groyne Renewal

After more than a year of community action to protect the beautiful Maroochy River from a devastating rock wall, in December 2017 the Sunshine Coast Council unanimously voted not to rock the Maroochy! Council agreed to stick with sandbags, which already work to hold off erosion while maintaining the natural beauty and access to the river.

This was a huge win for people power and a testament to the determination and strength of the Sunshine Coast community. Congratulations to Don't Rock The Maroochy, SCEC life member Jim Cash and the thousands of you who took action to save the Maroochy. This wouldn’t have happened without you.

What was this campaign all about? 

The Sunshine Coast Council adopted a 10-year Shoreline Erosion Management Plan (SEMP) in 2014 which clearly stated the existing geotextile groin field at the mouth of the Maroochy River is working as planned. The SEMP recommended Council stick with the existing groins, but consider replacing the geotextile bags with rock. SCEC have concerns with this recommendation as it has the potential to have significant negative impacts, including:

  • Increased bank erosion of the river bank
  • Loss of sand to beaches north of the river mouth
  • Increased current velocities of the Maroochy River adjacent to a popular caravan park
  • Reduction in natural amenity and user friendliness that the existing geotextile bags provide, thereby reducing the recreational value of the Cotton Tree Precinct. 

What were the options?

 

  • Replace bags as required. Since 2003 most of the bags have been covered by sand meaning little or no deterioration. This means only the top ones and end bags need replacing. This is by far the cheapest option and maximises the value of the existing asset. The Council's own commissioned study by the expert consultants estimates that only $150,000 to $200,000 is required to restore the groynes and extend their life by 8 to 10 years. 
  • Replace the existing structures with geotextile bags, bag for bag. If properly maintained geotextile groynes can now last up to 25 years instead of the 17 years this comparative study uses. If the 25-year figure is used in the comparison then bags become even more cost effective. 
  • Replace the existing structures with rock. The capital cost of rocks is over twice that of geotextile bags. Worth noting is that there is very little difference between the cost effectiveness of rocks ($19.76 million) to bags ($20.19 million) Table 5.4 Pb. 29 of the report. Rock construction raises additional questions which have not been addressed by this study:
      • Where will the rock come from and what will the cost be? It is believed the cost estimates for the rock are based on local sources that are no longer suitable and therefore underestimate the true costs.
      • No account has been made for the disruption to the Cotton Tree Precinct with the transport of rock onto the beach.
      • What will be done to avoid the reduction on natural amenity and user friendliness that the existing geotextile bags provide?

How does it all add up?

 

The report conducted by the Sunshine Coast Council only factors an estimate of remedial works around the campground, yet nothing for the northern beaches into its cost/benefit model. If it were to factor in the remedial work required for the northern beaches, it would make the rock groin option far less cost effective. Additionally, the report makes assumptions the groyne will reduce the cost of sand replenishment to Maroochydore beach by half. 

The report also attributes a benefit of over $1 million for the extra beach gained at Maroochydore without factoring in the loss of Flathead Point and loss of beach area to the north as negative outcomes. 

Cotton Tree is home to a world class, family friendly, recreational asset which has a sandy connectivity from the beach around to a safe estuary. A 200m rock groyne has the potential to negatively change this asset dramatically, thereby reducing visitor numbers and the tourist dollar.

Tourism is by far the most dominant benefit in the cost/benefit analysis. The report makes no mention of how these potential flow on effects could reduce visitor numbers to the Cotton Tree Precinct. 

A cost/benefit analysis that hasn't considered effects on tourism, significant additional remedial works and coastal processes affecting all Sunshine Coast beaches (not just Maroochydore beach) should be considered invalid without further study. 

Don't Rock the Maroochy Video

SCEC's Involvement over the last 20 years

 

SCEC has been a prominent voice over the last 20 years on issues relating to the dynamic nature of the Maroochy River. 

In the 1990’s the Maroochy River mouth was moving to the south of Pincushion Island and residents were concerned that the Cotton Tree infrastructure and Maroochy beach would be washed away.

There was a push to stabilise the mouth with training walls to the north of Pincushion.

SCEC was concerned about the effect this would have on environmental values and mounted a campaign to educate the community on the issue using historical records to show the Maroochy River mouth had oscillated about Pincushion Island going back to the 1850’s. 

Based on this, the Council of the day took the decision to allow the mouth to move back to the south of Pincushion along with the construction of the existing groyne field to ensure infrastructure was protected. It was decided to go with Geo Fabric Containers (GFC’s) instead of rock as this was more in keeping with the natural amenity of the estuary. 

The GFC’s were designed to last up to 25 years and are coming up for repair and/or renewal, which is why in 2017, the same debate we had 20 years ago has arisen once more. 

Read more about SCEC’s campaign efforts and continued involvement in this campaign here.