Wooli Coastwatcher, Edition 3.
Readers will be aware that our last Edition (2) reviewed the impact of beach scraping which was conducted along about 1.31 km of New Brighton Beach, in August-September, 2010. Sand was removed to a depth of up to 0.5 m. This was organized and paid for, by the Byron Shire Council (BIC). As also happened at Wooli, tidal and storm surge had depleted the dune mainly during 2009 and 2010. The outcome was studied and reported as “The New Brighton Beach Scraping Trial: Analysis of Dune and Beach Profile Data” by authors from the Water Research Laboratory, University of New South Wales.
Over a period of several days, three machines working in tandem rebuilt the dune by not only restoring sand volume but also by re contouring the dune to a natural slope (about 30 degrees). The result was a seaward gain of about 5 metres at the base of the dune. Although this activity did not necessarily create a seaward gain at the top of the dune, the existing dune top was subsequently better protected by the addition of sand as buffer. Where undertaken, subsequent plantings of Spinifex and other dune binding plants have assisted with retention of the sand. Natural longshore movement of sand restored sand volume where it had been removed by beach scraping.
Please see slideshow of images (new window) showing machines at work, with rebuilding and re contouring of the dune at New Brighton. Readers should also be aware that the beach at New Brighton is not as wide as that at Wooli; we have more sand at our disposal at Wooli. A backhoe is first used to remove and mobilize the top 0.2 to 0.5 m of sand, which is then moved and shaped by a tracked vehicle which has a blade at the front.
The second study performed reviewed the impact on life within the sand, and is titled “The Effects of Beach Scraping on the Infauna of New Brighton Beach, Northern NSW”, and is authored by Stephen Smith, Matthew Harrison, and Jennifer Rowland from the National Marine Science Centre, Southern Cross University, Bay Drive, Coffs Harbour, 2450. This report was prepared for the Byron Shire Council, June 2011.
Firstly, what are “infauna”? These are defined as “animals living within the intertidal beach”, and see below for description. I judge this 35 page report to be well assembled. . An accepted format is followed: Summary, Introduction, Methods, Results, Discussion, Acknowledgements, and References and is well worth a read. It sticks to the brief, without noticeable ideological bias.
Sampling techniques. I was interested to learn that there is an international scientific literature pertaining to beach scraping and associated study. There is plenty of work being done around the world on beach scraping. Pages 6-10 review sampling techniques. Later in the report, page 25 onwards, they review current approaches and justify theirs. Essentially, there were two control (away from the scraped section of beach) and two sampling sites. Post impact, sand was collected in a standardized way at day 1, 1 week, 2 weeks, and 1 month. A standard sampling technique was used. “Granulometry”–I will come back to this later–was also performed on sediment adjacent to sample site. Sand samples were sieved through a 1 mm mesh screen and preserved in formalin solution. On page 12 is a review of technique of sample preservation, formalin into ethanol, and larger particles Rose Bengal stain (a red stain which stains organic material pink), The reader is naturally impressed by the attention to detail in sample handling.
On page 29, there is a summary of species detected; and, in case you think the beach is inert, think again (though not to the extent of the monster sand worms in Frank Herbert’s “Dune”). Most numerous are Crustaceans called Isopods, and Amphipods; then Annelids sub group Polychaete. Well detailed. Statistical analysis was used to compare different populations, and asks the basic question “Was there any difference between the before, and the after beach scraping”. As well, the study design asks the more complex questions allowing it to “…assess impacts on the total number of animals (abundance), total number of species (species richness) and also the general change in community structure”.
Sample data was analysed using an advanced statistical technique called Permutational Multivariate Analysis of Variance (PERMANOVA).
Results. Firstly “…there was no consistent immediate effect of beach scraping on the community structure of beach infauna…”. And, secondly, “The results for the assessment of species richness and total abundance…indicated no effect of beach scraping on either measure”.
Further comment about sand granularity. Higher up the beach the sand has finer granules, and lower down closer to the water the grains are larger as wave action removes fine grain sand. As expected, the grain size changed after scraping, but this would appear to not have affected the infauna. The authors comment “…no significant biotic differences were evident”.
In their discussion, the authors refer to work by Schoeman, et. al, 2000 which indicated that recovery does not occur before a minimum of 2 weeks post impact. Although the authors allow for the possibility that this study was not sufficiently robust to detect changes (unlikely), they go on to comment, importantly, that “1. the highly dynamic nature of New Brighton beach is such that organisms are highly adapted to major changes in beach conditions (e.g. loss of sand from storms); 2. the type of impact was relatively benign in terms of factors that are known to affect beach infauna…”. Beach scraping does not remove sand from the lower beach/subtidal region, which is the origin of mobile crustaceans, which are then believed to be capable of quickly colonising disturbed areas.
Note, the overall conclusion on p. 26: “The results of this study clearly suggest that beach scraping, in this case, has no detectable effect on the biodiversity and assemblage patterns of beach infauna at New Brighton beach”.
Comment: Having reviewed both studies, I am now a stronger advocate of beach scraping for the purposes of rebuilding the depleted dune at Wooli. I stand by my previous comments that at Wooli, our dune is “sick”, as judged by the following features: 1. too steep a contour therefore unstable and at risk from what I call “duneslide”; 2. it has lost considerable volume, as happened at New Brighton in 2009 and 2010. This coupled with “1” means the dune toe is highly vulnerable to wave and tidal surge. And, 3. is in part covered by rubbish, and in other parts overgrown with Bitou so it does not have the natural stabilizing and sand aggregating benefits of binding plants like Spinifex grass and Native Morning Glory. Plus, 4., it is punctuated and thereby weakened by walkways that are not reinforced, as they should be, with sandbags and plantings. It is important, also, to consider that this study analysing “Dune and Beach Profile Data” should also allay fears that following beach scraping we are still able to live at the beachside in balance with nature.
The current Clarence Valley Council (CVC) “Wooli Beach Dune Rehabilitation Plan”, 2005, comments that the rehabilitation of the dune in the South Terrace area, at Wooli, is of the highest priority; yet, further along in this Plan they disallow beach scraping on “environmental” grounds. I would recommend the CVC authors review their plan in conjunction with this new information from the Byron Shire study in “The New Brighton Beach Scraping Trial”. Any new plan for Wooli Beach must take into account the positive benefits of beach scraping.
Approach and costs: There is no reason why CVC officers cannot reach out to their counterparts at BSC–isn’t that the job of our local body? The initial contact person could be Mr. Ben Fitzgibbon at BSC, as mentioned on p. 26. The cost is not great, some $160,000 to scrape about 1.31 km of beach; I believe about half of this cost was what was actually spent on the contract work. We have immediate access to the scientists that studied the outcomes at New Brighton…the methods and people are already here. We do not have to reinvent the wheel, we know what to do. And, we could go further, working with DuneCare to do, what has not been done to the necessary degree at New Brighton, the important “Part B”; which is to seriously plant the new dune so it stays around for many years to come.
Dr. Roger Welch
28 South Terrace,