Keeping an Eye on Bribie Island

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This week’s article considers coastal shoreline erosion and examines one option that has been very effective in halting erosion at Woorim.  This is the FFF fencing system developed by Bribie Island residents – scientist and engineer, Ian Bell, and businessman David Percival.  Their paper to the Queensland Coastal Conference in Cairns in 2011 and to the Growing Beaches conference on Bribie Island is reproduced with permission below.  This paper is being updated for presentation by the authors to the National Coast Conference in Brisbane in September 2012.

In response to community concerns following some significant erosion events in 2005, Caboolture Shire Council commissioned the highly respected engineering consultants BMT WBM to provide a shoreline erosion management plan to guide Council’s efforts.  The resulting Woorim Beach Shoreline Erosion Management Plan (WBSEMP) was adopted by Council without amendment in 2007.  The WBSEMP identified pedestrian traffic on coastal dunes as one of the greatest causes of destabilization and erosion of those dunal systems.  The WBSEMP recommended some method of restricting human access to the dunes as one of the most important erosion prevention initiatives that needed to be undertaken at Woorim.  Following the release of the WBSEMP, a number of Bribie Island community groups sought, and were granted, a $50,000 Federal Government Envirofund Grant for a programme of dune restoration including the installation of fencing to restrict human access to the dunes.

Coastal dunes change frequently during the seasonal cycle.  In the winter periods, winds pick up sand above the high-water mark and transport it higher into the dunes where it is trapped by vegetation in the fore-dune area and the dune “grows” as a result.  In the summer storm season, this added sand in the fore-dune area acts as protection for the rear-dunes and can be eroded away.  Any fencing that is installed in these areas has to be able to accommodate these changing conditions.

The FFF fencing system has a number of patentable features that allow it to adapt to the dynamics of the seasonal changes of sand accretion and erosion in the dune systems, and hence it was chosen as the appropriate fencing system for the Envirofund Project.  These design features are discussed at some length in the inventors’ paper below.  There has been considerable interest shown in this system and the inventors are in discussion with a number of groups regarding potential applications.

Despite the documented success and the adaptable design features of the FFF fencing system in preventing erosion at Woorim, MBRC removed a significant section of this fence in the early morning of December 27, 2011.  This was done supposedly for “safety” reasons which is a little difficult to understand.  The fence is well above Highest Astronomical Tide (HAT) and the special design features allow it to be adjusted vertically and relocated horizontally if necessary.  Despite speaking to many who walk and jog along that beach on a daily basis, MBI has been unable to find anyone who can recall any “safety” issues with that fence at that time.  So the reasons for its removal would appear to be a mystery.  MBI notes that MBRC’s CEO, Mr John Rauber, has given an undertaking that the fence will be replaced but that has not occurred at the time of posting of this article.

(Editor’s Note:  July 19, 2012 – Following the posting of this article on July 7, 2012, MBI has received advice from the office of MBRC’s CEO that the fence will be replaced before the summer.  MBI has also received advice from the Envirofund groups who initiated the fence in the first place, that they have not been consulted regarding any changes to the fence when it is put back.  The fence is therefore expected to be put back as it was originally constructed except for the minor changes discussed at the Growing Beaches conference on Bribie in April 2012.)

Editor, MyBribieIsland

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WOORIM BEACH, BRIBIE ISLAND, AND THE REVOLUTIONARY “FFF DUNE FENCE”

David Percival1 and Ian Bell2

1 President Friends of Woorim Beach  2 Project collaborator and inventor

ABSTRACT

A revolutionary new fencing system for fencing dunes is presented which works in harmony with the ever changing shape of the dunes and foreshore to provide a flexible solution to the challenge of reducing human pressure of these sensitive areas.  This need arose during a Coastcare project at Woorim Beach Bribie Island undertaken by the “Friends of Woorim Beach”.  Two years’ of results from the planting of thousands of dune plants with protection by the new “FFF dune fence” are presented along with detailed design features and benefits.  Some of the challenges that had to be incorporated into the fence included that it must not interfere with the nesting of endangered loggerhead turtles, be unobtrusive and inexpensive, and be simply relocatable in both vertical and horizontal directions as dune shape and foreshore are altered over time.

INTRODUCTION

This Project “The Woorim Beach Dune Stabilisation Project – Bribie Island, South East Queensland” was funded under the Australian government’s Envirofund “Coastal and Marine Grants” program and was initiated by the community group “Friends of Woorim Beach” (FOWB).  Moreton Bay Regional Council is a contributor to the project providing 2.5 km of fencing and labour.  Wallum Action Group community nursery provided 25,000 native plants.

The project was highly commended in the Sunshine Coast Environment Council Awards 2010.

THE PROBLEM

 Woorim Beach has been subject to severe erosion over many years.  The latest erosion occurring in 2005/06 as can be seen in Figures 1 & 2.  Sand was pumped to reclaim the beach as shown in Figure 3 leading to eventual recovery as shown in Figure 4

Fig 1 - Woorim Beach erosion 2005

Fig 2 - Woorim Beach erosion 2005

 

 


 

 

 

Fig 3 - Woorim Beach sand replenishment

Fig 4 - Shows partial recovery of dunes following severe erosion of 2005/06

 

 

 

 

 

 

 

 

 

As shown in Figure 4 the foreshore, although restored, has reduced resilience against future erosion due to the sparse vegetative cover.  The original fence erected to exclude trampling has become completely buried, requiring the construction of a second fence which is also becoming buried.  This results not only in loss of function and investment but also creates a danger with partially exposed wires and the sharp ends of steel pickets.

HUMAN IMPACT ON DUNES

The images of degraded foreshore shown in Figures 4 & 5 are unfortunately a common sight along much of the Australian coastline.

There is a tendency to become familiar with such sights and to perhaps think of these as just part of the normal cycle of coastal erosion and deposition.  However on Bribe Island such foreshore degradation is almost uniquely associated with areas of greatest population density and beach use and is largely constrained to the 3 kilometre long developed area.  This is most likely not a solely natural occurrence.  This proposition is supported by the contrasting scene of largely intact dune and vegetation associations along the entire 20 kilometre long remainder of the eastern shoreline to the north adjacent to uninhabited natural areas as shown in Figure 6.

Fig 5 - Typical foreshore at dense population and high use area - South Woorim Beach

Fig 6 - Typical eastern ocean foreshore along uninhabited approx 20km of Bribie Island

 

 

 

 

 

 

 

 

The same general pattern of exacerbated dune and foreshore erosion coinciding predominantly with areas of highest human presence and activity is a common theme, not just on Bribie Island, but around Australia’s coastline generally.

The dominant main vegetation systems – Casuarina equisetifolia (She Oak) along the top of the dunes and Spinifex sericeus (Beach Spinifex grass) along the face and toe of the dunes are critical to the maintenance of these natural dune systems.

Beach Spinifex grass performs the simple yet remarkable role of trapping thousands of tonnes of sand as it blows up and down the beach forming a deep, wide fore dune toe that acts as a sacrificial buffer protecting the main dune.  She Oaks are an essential partner as they trap further sand that escapes the Spinifex grass during very strong onshore winds and hold the main dune together.

These functions form the most basic starting principles required for effective foreshore management, yet it is surprising how commonly these basic principles are being ignored with the sort of result depicted in Figure 7.

The success of the Friends of Woorim Beach Coastcare project is based on these simple principles entailing mass plantings in combination with effective exclusion of beachgoers from the dunes using a new fence design as shown in Figure 8.

 

Fig 7 - Dune loss and windblown sand following removal of dune vegetation for views - Woorim Beach

Fig 8 - End result of FOWB Coastcare project

 

 

 

 

 

 

 

 

SIMILARITIES BETWEEN STREAMBANKS AND OCEAN FORESHORES

Many of the principles adopted to manage damage to the dunes were derived from detailed studies undertaken by the project “Management of Stock Access to the Riparian Zone” (Bell & Priestly 1996) as discussed below.  Figures 9 & 10 show a stream (Buffalo Brook) in northern Tasmania which was one of the study sites for that project.

Figure 9 shows the stream prior to fencing in 1988 to prevent stock from accessing the stream.  Such degraded scenes are common throughout rural Australia and we have become familiar with them just as we have with degraded foreshores.  However, as with the impact of humans on dune systems, the linkages between the cause and resulting degradation by stock to stream banks tends to be under recognised.  It is not until stock are totally excluded from the stream as was done at this location that the stream recovers and vegetation regenerates to the condition shown in the photo in figure 10.  Both photos were taken at exactly the same location.  All regrowth was achieved through natural germination with no planting.

Fig 9 - Buffalo Brook 1988 showing stream condition under conditions of unhindered access by stock to stream

Fig 10 - Buffalo Brook 2004 at same location as in Fig 9 following complete fencing along stream to prevent access by stock

 

 

 

 

 

 

 

 

Figure 11 shows the important role of vegetation in ensuring stream bank stability.  The upper bank is stabilised by larger vegetation – trees and shrubs, while much smaller and seemingly less significant species such as reeds and aquatic plants stabilise the toe of the bank.  However whilst these small species may seem insignificant they play a crucial role in preventing the commencement of stream bank erosion by a process of toe erosion and undercutting that can eventually undermine the larger vegetation on the top of the bank.  It’s the same with dune systems.

Fig 11 - The role of vegetation types in protecting both the top and the toe of the stream bank from erosion and undercutting

Fig 12 - The new "FFF" foreshore fence design as adopted for the project

 

 

 

 

 

 

 

 

Following are the key principles established from studies on managing stream bank erosion by stock that are directly transferable to managing damage by humans to coastal dunes.

1. Much of the impact seen is insidious and there is a tendency to accept this as part of the normal Australian landscape.  Cause and effect connections tend to be under-recognised resulting in severe degradation and costly remediation by engineering works.

2. The simple act of excluding the impact of trampling and damage to vegetation can bring about a remarkable recovery to a more natural state that is more resilient to the forces of nature.  Overall aesthetics and amenity of the area are greatly improved and important habitat for wildlife is provided.

3. Fencing that can withstand nature’s forces is critical in protect stabilising vegetation.  To deal with the challenge of fencing out stock in such in such an aggressive area as a floodplain, it was necessary to develop new fencing designs and principles to replace the old failed systems that have been the weak link in ensuring stream bank protection.  The resulting new flood-proof stock fence was featured on the ABC TV’s New Inventor’s Program – Episode 11 on 19 May 2004.  Similarly a completely new fencing system was required to address fencing in the challenging foreshore environment – the “FFF dune fence” which was invented specifically for this project.

4. The amount of damage done to the vegetation by trampling (by stock or humans) is proportional to the number of intrusions into the area and the time spent in that area.  However it might not be essential to totally remove all sources of impact at all times in order for the vegetation to survive and flourish.

5. With suitable fencing protection and adequate and appropriate plants and density, the natural protective vegetation recovers effectively with minimal intervention.

NEW FORESHORE FENCING SYSTEM – THE “FFF DUNE FENCE”

The “FFF dune fence” is being adopted by some councils in Queensland.  Feedback to date has been that the fence is very quick and simple to erect and is much less expensive than traditional fencing due to lower cost of materials required and significantly reduced installation and maintenance costs.  This simple and robust design ensures that the fence will not be subject to becoming a lost asset by becoming buried.  The “FFF dune fence” should last for several years and assist in the accumulation of vast amounts of sand to commence the dune formation process.

As shown in Figure 4, traditional fences are not suited to the beach and become buried by accumulation of sand, eventually rendering the fence useless with the considerable investment in kilometres of fencing wasted.  Buried fences also create a dangerous situation for beach users.  Clearly a completely different approach is necessary in fencing along the foreshore.

This new fence enables adjustment of fence height to suit the changing shape of the dunes by sliding the steel star picket either up or down the wooden post after releasing the chain retaining screws.  Four wires are adequate to provide an exclusion zone. It is recommended that suitable signage be attached centrally in each span to explain the purpose of the fence and to highlight the presence of the wires.  Other visible indicators such as streamers are recommended.

Wires can be retensioned is necessary by adjusting the ratchets at either end of the wires.  The timber posts are 4 metres long, pointed and driven 2 metres into the sand.  Because only minimal wire tension is required and with the posts 2 metres into the sand, there is no need for a conventional double post end strainer assembly.  However a 600 x 150 x 50 mm thrust block is required to be buried approximately 500 mm deep against each end post to provide additional support against the strain of the wires.  This is also required at any change of direction.  Post spacing is nominally 25 to 50 metres and at the main high and low points along the foreshore.  With longer post spacings it is recommended that droppers be used to maintain wire spacing.  Closer spacing of posts has the benefit of possibly avoiding the need for droppers.

The alignment of the fence is chosen so that the posts are located on an existing rise or dune formation with the intention of commencing sand reclamation and dune formation towards the sea.  Posts must be above maximum high tide level such that the buried portion of the posts is never in saturated sand as this would result in loss of rigidity and movement.

As sand becomes deposited following the resultant advance of stabilising grasses the shape of the dunes will change and some posts will become slowly buried.  Once there is no more height available on the timber posts to continue to raise the attached steel post, the timber post can be jacked up as required as long as the original 2 metres depth is maintained.  Similarly if some posts become more exposed they can be re-driven to their original depth, however deposition rather than erosion will be the normal trend.

If required the entire fence can be dismantled and relocated by detaching the steel posts and attached wires, removing all timber posts and relocating.  This is desirable to facilitate the continued seaward advance of the dune which is a natural resulting trend following the erection of the fence and the spread of dune grasses which entrap the wind blown sand.

The fence has been designed to provide a much safer environment with no sharp protrusions and nothing to cause tripping as can occur when traditional fencing is employed on the foreshore.

This design, with only a minimum of wires (nominally 4) and explanatory signage, is sufficient to discourage the vast majority of beachgoers from entering the dune area resulting in recovery and expansion of protective vegetation.  The fence is turtle friendly allowing access under the bottom wire for nesting.

Fig 13 - Intermediate post

Fig 14 - Single end strainer post at walkway supported by thrust block

 

 

 

 

 

 

 

 

 

 

 

 

The design and information provided on the “FFF dune fence”, which are totally new in concept both nationally and internationally, are not subject to any patents or patent applications and are provided freely in good faith to all potential users under the following conditions:

1. No responsibility or liability is accepted by the project or those involved in the design of this fence.  Any claims that may arise as a result of the installation or use of the fence, or any variations, is the owner’s esponsibility.

2. In any mention, use or application of the fence as shown herein, credit is given to “Friends of Woorim Beach Bribie Island and Ian Bell (inventor/desiger) & “FFF Fencing” TM

TAKE HOME MESSAGES

The basic and commonly overlooked concept of maintaining, protecting and growing the natural dune profile and associated vegetation communities that exist prior to development and encroachment by humans is crucial to successful foreshore management.

The simple yet fundamental role of naturally occurring native plant species along the top of the dunes and on the foreshore dune and toe are critical to maintaining a natural buffer of freely available, self regenerating sand reserve against the regular assaults of the sea including storms, cyclones.  In south-east Queensland, examples of these key species are Casuarina equisetifolia (She Oak) on the main dune and Spinifex sericeus (Beach Spinifex grass) on the foredune.

Once these natural dune systems are lost, the foreshore becomes much more susceptible to undermining and collapse with the loss of huge volumes of sand which then threatens foreshore beachfront property and infrastructure. The resultant emergency created by this state of imbalance and loss of natural buffer is often a significant factor in council expenditure on millions of dollars to construct expensive engineering barriers and treatments.  Such works may not only be unnecessary, but they also detract from the natural beauty of the foreshore and its function as an important part of the ecosystem.

Throughout Australia, achievement of effective foreshore protection by preserving and enhancing the essential function of natural dune and vegetation systems, particularly in high use areas, has been severely limited.   Two main factors are responsible for this:

1. Lack of understanding by foreshore managers of the essential role and function of natural dune systems.

2. The unavailability of a suitable fencing system for this harsh and changing environment.

The new “FFF dune fence” addresses the second problem and hopefully opens to door to a new era of natural dune preservation.

REFERENCES:

Bell I, Priestly T, (1998)  “Management of Stock Access to the Riparian Zone” a project under the Rehabilitation & Management of Riparian Lands R&D Program.  Land & Water Resources Research and Development Corporation. Canberra.

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