Submission to Community Consultation
Don’t Rock The Maroochy Submission to Community Consultation Meetings & Maroochy River Estuary Consultation Group
We have been closely following the issue of the Sunshine Coast Council’s proposals on what needs to be done regarding the existing geotextile groyne fields at Cotton Tree at the mouth of the Maroochy River … and note council has established the Maroochy River Estuary Consultation Group.
We have applied for representation on this group and as yet have not been advised if either of our 2 applicants have been successful.
We note that council is looking at spending a considerable amount of rate payer’s money on the solution to stop future erosion at the mouth of the Maroochy River and thereby protect valuable assets.
We contend that rather than ad hoc funding of new projects in specific areas, council needs to step back and re-evaluate, by looking at the situation holistically, before substantial sums of money are spent.
To understand what we mean, requires us to look back in time to where these coastal management problems began and although the beaches have always been eroded though weather and swell events and naturally replenished over time, it was the construction of the rock walls at the mouth of the Mooloolah River in the late 60’s that has had a long term effect.
We appreciate these walls were needed, as it was imperative to be able to cross an often treacherous bar day or night and in all but the most extreme conditions, to safely transport marine pilots to the ships waiting off Mooloolaba for pilotage to enter the Port of Brisbane.
However, as is usually the case when rock walls are built at coastal river mouths, they interrupted the natural northerly sand drift and there was a gradual loss of sand along the beaches at Mooloolaba, Alexandra Headland and Maroochydore.
By the early 2000’s, this sand loss had contributed to bad erosion at Cotton Tree at the mouth of the Maroochy River, which required action, or valuable assets like the Cotton Tree Holiday Park would be lost.
Substantial sums of council money were invested in conducting studies and modelling to come up with a solution to the problem, which was the design and installation of the existing geotextile groyne fields at Cotton Tree.
These geotextile groynes have done the job they were designed to do and earlier this year, Council commissioned a condition report on them from ICM (International Coastal Management, the company that designed the groynes).
ICM inspected the groynes in March 2017 and delivered their condition report to council the following month.
This ICM report is extensive, but in summary … it states:
- The existing geo textile groynes are still working and doing the job they were designed to do … and the containers (bags) in at those groynes that are sound have a total life of 25 years or longer.
This assessment means that since they were installed between 2000 & 2003, ICM estimate the sound containers have 8 - 10 years working life still left in them.
The following info is from the executive summary of the ICM report regarding the state of the existing geo textile groynes:
- Across the seawall and the four groynes, a total of 315 containers were compromised, including:
- 31 damaged containers (repairable)
- 66 damaged (non-repairable)
- 51 displaced (potentially reusable)
- Approximately 167 missing bags (from the initial groyne design).
- This equates to about 5% of an estimated 3,500 containers.
- A preliminary estimate of cost to restore the groynes to original design is $150,000 - $200,000, using the same size containers and fabric as the ones that are there now.
Despite the information in this report, council engineers appear to consider that the existing geotextile groyne field is at the end of its working life and in providing the brief for a council commissioned Cost Benefit Analysis from JB Pacific, seem to have ignored as an option, the repair/replace/maintain information provided by ICM.
The options detailed in the JB Pacific Cost Benefit Analysis are:
- Removal of the existing geo textile groynes and replacement with new geotextile bags – capital cost 2.6 million dollars
- Removal and replacement of the existing geo textile groynes and replacement with new rock groynes – capital cost 5.73 million dollars
- Construction of a new 200m long seaward facing rock groyne at Cotton Tree – Capital cost 4.09 million dollars based on concept design only
- Re-establishment of a northern river channel for the Maroochy River, by the mechanical re-construction of a beach connecting Pin Cushion Island to Cotton Tree – Capital cost 7.53 million dollars based on concept design only
- Re-establishment of a northern river channel for the Maroochy River, by the construction of a new rock breakwater connecting Pin Cushion Island to Cotton Tree – Capital cost 8.47 million dollars based on concept design only
- Further to these expensive options, there has over the years been considerable money spent on dredging operations to remove the sand which builds up either outside, or inside the Mooloolah River mouth and pumping it onto the eastern end of Mooloolaba Beach.
What has been seen, is that rather than drift north and replenish the beaches, this dredged sand very quickly migrates either back into the river mouth, or builds up outside the rock walls.
Dredging at considerable cost has also occurred in the mouth of the Maroochy River. Initially to remove sand from the north side of the river mouth to assist the river draining to sea on that side of the river when the geotextile groyne field was installed … and since about 2015 from the south side of the river mouth, with the dredged sand being pumped onto Maroochydore Beach for beach replenishment.
We believe that before substantial amounts of money is spent on new groyne fields, that council steps back from this ad hoc approach of expensive band-aid solutions and in conjunction with State Government, fund and commission an extensive study on the relatively small stretch of coast from Point Cartwright to Marcoola, to see if a more sensible holistic approach could be developed to solve problems, which are currently being treated in isolation.
We accept that there has been a number of studies done in the past on how best to solve the problems being encountered, but there has never been one that addresses the cause and effect processes that come into play though the interaction of the whole stretch of coastline from Point Cartwright to Marcoola.
Such a study should incorporate all research and knowledge already paid for in the past, be undertaken by scientists, engineers and imminent academics with experience and expertise in hydrology, coastal management and coastal engineering and involve all aspects of current world best practices in coming up with a coastal management plan, that values the attraction of natural attributes and encompasses the health and good management of the Mooloolah and Maroochy River systems and their surrounding beaches.
In closing … we submit the following
- Council should spend the 150-200k suggested by International Coastal Management to bring the existing groyne field back to original design, which will extend its working life beyond 10 years
- Dredging operations be reduced to an as needed basis only, until a scientific study provides a greater understanding of how the whole system works, enabling an action plan to be developed that will be economically smart and deliver the best possible result.