Good Intentions, Unintended Consequences
Since 2015, Swellnet has published a series of articles on the damage caused by marram grass. An introduced species, marram was planted to stabilise shifting sand dunes, which it does, yet it also does many other things that only came to light afterwards.
The following is a case study of marram grass, how it changed a dune system, and the surf in front of it.
Just a few hours north of Sydney lies a quiet corner of the coast that many surfers will be familiar with. It sits on a promontory that juts east into the Tasman Sea, making it a magnet for any swell arriving from the south around to the north. The semi-isolated hamlet of Seal Rocks has long been a rite of passage for surfers from Sydney and beyond.
For Sydney surfers, it's close enough for a weekend jaunt but also far enough away to feel like a proper road trip. It offers camping, fishing, and surfing on pristine beaches where the thought of what lurks beneath electrifies even small wave sessions.
Just beyond Seal Rocks, where the bitumen road turns to dust, lies Treachery Camp. 'Treach' has basic camping facilities - though it also has new upgraded cabins - located in a naturally beautiful environment. The camp sits just behind the dunes that front onto Treachery Beach with a Melaleuca forest found deep in the back reaches. The beauty about Treach is that it's offshore in the summer nor'easter, while also sucking in all available south swell, the combination serving up A-frame peaks more often than not.
Jon Brown is the current manager of the camp. Jon's grandfather, John (Jack) Henry Brown, acquired the land from the original land-holder in 1964. It was part of the NSW Government's Returned Soldiers Settlement Act, which was brought in following World War I and extended after World War II offering Crown Land at discounted rates to soldiers who served overseas.
Jon is now the third generation of his family to manage Treachery Camp since it's belonged to the Brown family. My own experience with Treachery is but a fraction of this time, but still, I've got many memories of pumping surf tucked away in the corner of the beach. However, those classic days have become less frequent over the past half a decade.
The reason becomes clear when checking the surf from the 'lookout' at the top of the hill...
Treachery Beach is open to both southerly swell and the prevailing southerly winds, the combination of which have created an expansive coastal dune system that extends over 300m from the beach towards the campsite. One back dune pushes even deeper inland and right onto the perimeters of the campsite.
During the 1990's this back dune started to encroach on the campsite at a rate of 1-1.5m/year. So, driven by good intentions, Jon's grandparents enlisted the help of Dune Care and got busy planting various species of vegetation across the dune system to stabilise the sand and stop it moving any further onto their property.
The chosen species included marram grass, an introduced species which is highly effective at propagating across sand dunes, trapping the sand, and stabilising the system. Just what the Browns wanted.
Similar revegetation techniques were used by sand mining companies following rutile mining operations up and down the East Coast, with one such mine operating down the beach to the west-southwest, on the boundary of the Brown's property in the 1970's.
The problem with marram, however, is it does what it's supposed to do, and more. It will propagate and stabilise a dune system, but it will also be detrimental to the local ecosystem, pushing out natives like spinifex.
When marram grass takes hold of a beach, the dunes become higher and steeper than those covered by native spinifex due to its clumping, heaped nature. Spinifex spreads out more evenly across the dune system and creeps into hollows, creating a more uniform system. These higher, steeper dunes are at increased risk to erosion and blowouts and result in large scale scarping which then rebounds the incoming swell energy back into the nearshore zone.
From a surfer's point of view, marram traps more sand above the tide line at the expense of sand below it, meaning banks are generally deeper, plus the steeper beach profile makes for increased backwash, all of which deteriorates surfing amenity. Sand availability is limited and wave quality diminished at locations where marram grass dominates the dune system.
While initially celebrated for its stabilisation capabilities and in use since the 1970s, it wasn't until late in the century that coastal authorities to realise the damage that marram causes. From being actively planted through the 1990s, coastal managers witnessed marram out-muscle native species, adversely impact the natural dune biodiversity, and also alter the beach profiles. Since the early 2000s, marram has been classified as invasive and it's now discouraged from use in dune restoration activities across Australia.
When the marram was planted at Treachery in the mid-90's it quickly did the job it was supposed to do, preventing the dune system from encroaching on the camp site. The Brown family and Dune Care ceased the dune stabilisation program around fifteen years ago, but the marram had created a foundation for further growth of vegetation growth. The spread across the system is clear to see in the satellite imagery at the end of this article.
While my personal experience of Treachery surf checks date back just over a decade, photos from earlier show how successful the transformation of the entire dune system has been, even though the most rapid changes have occurred in the past ten years.
Usually a quick walk to the lookout tree and one step up would give you a good overview out the front and in the corner, but if you wanted to scope the whole beach, you'd only have to walk another 75 metres or so along the track on top of the main sand dune. On confirmation of pumping A-frames, the walking paths down through the dunes would provide additional views of the surf in front of you.
What now confronts eager surfers is a barrier of thick coastal shrub, metres high and blocking any view of the ocean whatsoever, let alone the surf.
Beyond the marram grass doing the initial stabilising, native wattle and tea tree started to establish, followed by banksias and finally eucalypts. The regent bowerbird along with honeyeasters helped propagate seed, with fresh water provided by a small lagoon sitting between the foredune and backdune.
The whole upper part of the dune is now impenetrable while lower parts are heavily vegetated, leaving the frontal dune system with a thin ribbon of native spinifex.There is now far less exchange of sand between the beach and the surf zone.
From Jon's accounts, and my own personal experience, the impact on the sand banks and quality of surf has been to the detriment as there's less sitting out in the surf zone. Owing to south swell exposure, the banks at Treachery have always shifted around, yet the amount of quality surf days have dropped away considerably. A once reliable go-to spot in summer has now become more fickle.
Such is the density of the new vegetation, Jon and his family concede that only a really intense (hot burn) fire would be enough to at least get access and see the dune again - but the fire would most likely take the camp with it.
Satellite imagery of the region from Yagon to the west and Lighthouse Beach to the east show the dune systems being engulfed between 1990 through 2020. The largest differences have been seen through the last two decades.
Tellingly, the sand blowouts at the eastern end of Lighthouse Beach haven't changed at all, due to the lack of dune restoration works on that beach.
There's not much than can be done from here besides walking down through the tunnels of vegetation to the surf and taking notes regarding what to do and what not to do with future dune restoration activities. That being, the continued planting of native spinifex while avoiding marram grass at all costs. This is the only choice for dune systems to remain in a more natural state.
A big thank you goes out to the greater Brown family from Treachery Camp, especially Jon for digging through the old photo archives.
Read our 2015 article on the effects of marram grass here: Damned Marram: Not All Grass Is Good For Your Surfing