Submission to Sunshine Coast Council – Don’t Rock the Maroochy

Download a copy of the submission here.

About Don’t Rock the Maroochy

Don’t Rock The Maroochy is a group of concerned locals and visitors to the area who are extremely concerned that the Sunshine Coast Council proposal to replace the existing geotextile bag groynes at Cotton Tree on the south side of the river mouth with rock walls and possibly building a 200m rock wall seaward, will forever change and destroy the natural beauty and enjoyment of the area.

Our group come from all walks of life and believe that Maroochydore’s greatest assets are its beaches and natural river. 

We are not for profit, nor politically aligned or driven by any other agenda other than seeking to not destroy what we all enjoy.

Our objectives

Our belief is that more can achieved by rational discussion and examination of facts, than taking a more adversarial approach and to this end we are engaging in conversations with individual councillors regarding the matter.

Our submission

In compiling this submission, we have studied in detail 2 documents:

  • The Technical Memorandum to Council from BMT WBM, titled Maroochy River Mouth Coastal Management – Preliminary Options Assessment – 21st June 2016.
  • The Shoreline Coastal Management Plan (SEMP) from BMT WBM – 2014.

After studying both these documents and seeking advice from coastal engineers with knowledge in this area, we note that both documents state that the building of rock walls, or the replacement of existing geotextile bag groynes with rock groynes, are not preferred options.

We note that SEMP was adopted as council policy in 2014.


All information we have been given, or have found through research, is that the proposal to build a 200m rock wall seawards from Cotton Tree is driven by a need to reduce the cost of sand pumping for beach replenishment on the Maroochydore - Alexandra Headland stretch of beach.

If this is the case and we have no reason to doubt that, it seems on basic examination of costs, that building a 200m rock wall will cost a huge amount of money and will not be cheaper than continuing beach replenishment in its current form. 

Costing 200m Rock Wall

After examination of the Technical Memorandum to Council from BMT WBM, titled Maroochy River Mouth Coastal Management, we submit there are many areas which should be considered carefully before any decision to proceed with a 200m rock wall is made.

The document clearly states that assumptions on data which final costings will be arrived at, will require the project moving from pre-concept design stage which it currently is, to the next stages of concept and detailed design, which in itself will be an expensive exercise.

The document also considers a 40% cost contingency, highlighting the uncertainty of accepting costings arrived at in the pre-concept design stage.

Final costing increases could likely become even larger than the suggested 40%, as more information is collated on:

  • Nearshore significant wave height.
  • Storm tide conditions.
  • Climate change induced sea level rises.
  • Availability of suitable rock.
  • That Cotton Tree Holiday Park, which is listed on the Queensland Heritage Register,  possibly requiring long term ongoing protection (e.g. seawall structure) due to anticipated erosion down drift of the proposed wall.
  • Mitigating sand loss due to downdrift erosion created by the rock wall to the beaches north of the Maroochy River mouth.
  • Short and long term effect on the current structure and environment of the river upstream of the mouth

Other considerations

Without a doubt, the enjoyment and prosperity of the Maroochydore area is intertwined with the beautiful natural state of the Maroochy River.

Apart from cost blow outs, the down side of building a 200m rock wall seaward from Cotton Tree is that it would forever change this beautiful area and would detract from what attracts locals and visitors to the area.  Once built … a rock wall can’t be unbuilt.


We submit that the proposal to build a 200m rock wall seaward from Cotton Tree should not proceed any further on the basis that the downsides of building such a wall will defeat any perceived good it could do … and the high probability of massive cost blowouts.


The existing geotextile bag groynes were put in place as a result of a great deal of research and modelling done by the Maroochy River Entrance Working Party, put together by council some 20 years ago to address the problem of erosion at Cotton Tree.

The geotextile bags have proven to have done the job they were designed to do by stabilising sand in front of the Cotton Tree Holiday Park, helping to assist the southern entrance to the Maroochy River sand up and thereby assist the river to drain seaward through a northern entrance on the south side of Pin Cushion. Although some geotextile bags are damaged and require replacement, the majority of them are still in good shape and doing their job.

Geotextile Bags v/s Rocks

As stated previously in this submission, the greatest assets Maroochydore has are its beach and the natural sandy river.

Since they were installed, the geotextile bags have created a family safe beach in front of the Cotton Tree Holiday Park and is enjoyed by locals and visitors to the area.

Literally thousands of kids have played and learnt to surf there, as the area is used by surf schools and being able to safely run over and play around the geotextile bags is a very important aspect of the family attraction.

To replace these geotextile bags with rocks would totally reverse that situation and create potential dangers for kids and families and greatly detract from the area’s value and enjoyment.

Although some geotextile bags are damaged and need replacing, most are in good order and have plenty of working life left in them.

Cost comparison Geotextile Bags v/s Rocks

Any cost comparisons done between maintaining/replacing the existing geotextile bags and building rock wall groynes must include the following:

  • An engineering audit of the state of the current geotextile bags
  • Removal and disposal of the existing bags.
  • Preparation of the area for rock replacement.
  • Cost of sourcing suitable rock.
  • Loss of value to the area by turning a safe haven into a potentially dangerous area for families.
  • Possible legal liability council may experience by building the rock walls in a public place.
  • Assessment of the effects of rock groynes compared to geotextile bag groynes.


We submit that when considering all aspects, including the loss of public amenity, the cost of maintaining/replacing the existing geotextile bag groynes will be far less than replacing them with rock … and respectfully urge the council to adopt this approach


We firmly believe that the beach is a very important component in the attraction to and prosperity of the area and it is the expectation of residents and visitors alike that there will be beach to enjoy, rather than exposed coffee rock which occurs after big swell events.

Cost comparison Sand Pumping v/s 200m Rock Wall Seaward Groyne

We believe that as the infrastructure is already in place to pump sand from the Maroochy River mouth onto the beach when it’s necessary to do so, it will be much cheaper to continue doing that, than the cost of constructing a rock wall, which will be many millions of dollars.


The only input we submit on this matter is that any sand pumped from the Maroochy River onto the beach, be taken from areas on the north side of the river mouth, thereby assisting the river entrance in remaining to the north around Pin Cushion, rather than from the south side of the river mouth, which detracts from the good work being done by the geotextile bag groynes in trapping sand on that side of the river entrance.

We realise that this may be more difficult due to the north side of the river mouth being in a gazetted Fish Habitat area, but believe once the whole situation was explained to the relevant Qld Government departments, that permission would be given.


Thank you for taking the time to read our submission and we respectfully hope that you take on board our thoughts and suggestions, which have come from a wide cross section of the community who love and appreciate where we live.


Mal Pratt & Bryan Weir

Don’t Rock the Maroochy

Download a copy of the submission here.