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mccnmatt

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May 13, 2016

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Geology, kayaking, national parks, Native birds, natural history, Uncategorized, waterways

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Delta bravo!

Kylie’s Beach in Crowdy Bay National Park

It’s lucky that travelling in reverse is just as easy as going forwards in Egg, my decrepit wooden kayak (currently held together with duct tape), because lately my paddles seem to be taking me back in time. Back to old haunts and old holiday snaps, but also really really far back into the geological past.

When I took this photo of beautiful Kylie’s Beach in Crowdy Bay National Park in 2011, for instance, I wasn’t thinking “My, what a fine example of a barrier dune system in a wave dominated estuary!”

Diamond Head and Watson Taylor Lake

And this snap from North Brother Mountain, taken on the same trip five years ago, demonstrates that I wasn’t paying enough attention to geomorphology at the time. It’s not a bad shot of the 100,000 year old Pleistocene sand barriers that protect Watson Taylor Lake from the crashing waves of the Pacific. But, in retrospect, I should have given the picturesque tree on the right the flick, and made sure I squeezed in a view of the mouth of the Camden Haven River.

Because, for the New South Wales anyway, this is a pretty special place. As you can see in the pic below by a more geologically literate photographer, enfolded in the lake is a classic river delta – a rare sight in this part of the world. It’s a mini-Mississippi, sloughing off its sediment as it flows into stiller waters, leaving muddy banks along the way and a cluster of little islands at river’s end.

Watson Taylor Lake. Bias, Gene. watsontaylorlake.jpg Pics4learning July 2004. 9 May 2016 <http://pics.tech4learning.com>.

Sad to say, I didn’t notice all this deposition and composition as I paddled down Camden Haven Inlet at dawn, skimming over the seagrass and the sand. Even when I got stuck in the mud – sorry, fluvial sediment – right in the middle of the lake. At high tide. Next to a bunch of knee deep swans. Sometimes I reckon I’m not the sharpest knife in the knifeblock.

Black swans smirking while I try to get afloat after running aground in the middle of the lake

It was only back at camp at Kylie’s, over a first reviving brew-up, when I stumbled on Rod’s Northern Rivers Geology blog with its intriguing story of the missing coastal deltas of New South Wales that I figured out what I’d seen.

South Brother Mountain in dawn light

Up a shallow side creek towards the lake

South and Middle Brother from the northern shore of the lake

A side view of the levees beside the Camden Haven River

Paddling dead casual-like towards the river mouth

Thinking back, I realised I’d been somewhere very similar just a few weeks ago, in another one of the New South Wales’ magical coastal lagoons. Where Dora Creek – home of freakish panda-snakes – empties into Lake Macquarie, the very same levees march, both sides of the river, far out into the open water.

Dora Creek doesn’t have mangrove topped islands at its mouth, like the Camden Haven. Perhaps their beginnings were washed away by the waves that scoot across five kilometres of open water to scare the hell out of unwary kayakers. In the same way storms, waves and the East Australian Current sluice river sand and sediment out into the Pacific or up the coast, leaving barrier beaches in place of river deltas all along the Eastern seaboard.

Island in the delta

But in the sheltered estuary of Watson Taylor Lake I got to enjoy all the rare pleasures of a river delta. Mosquitoes, for instance. More than I’ve encountered anywhere, even my backyard, locally famous for its blood buffet and chubby and contented microbats. With the mozzies come the mozzie eaters.

“Clumping” white-breasted woodswallows

Woodswallows peeping

Woodswallow grooming

I stopped to take pictures of the wood swallows, but in fact, this little beach, at the very end of the Camden Haven’s levees, had almost as many birds as it had bugs. Honey-eaters in an array of colours: brown, striped and yellow-faced. Noisy friarbirds, mobs of them, bursting from the casuarinas to wheel and chatter. Wagtails and fantails. Crested terns chilling out away from the surf. A drongo (I’m not being insulting – it’s a gorgeous bird). Not to mention a special treat – the rarely sighted fungus-faced thornbill.

Egg on “bird watching beach” near the mouth of the Camden Haven River

Spangled drongo

The rarely sighted fungus faced thornbill

Crested terns sticking their tongues out at me.

And, as I wended my way through the maze of islands with the help of the handy map in my Paddlers Guide to NSW, an unflappable young sea eagle, rising majestically above the cloud of biters. It takes a genuine love of raptors to continue taking snaps while half a dozen mosquitos are sucking on your eyelids.

White bellied sea eagle in a river-side casuarina

Juvenile white bellied sea eagle

But as RB just reminded me, if Australia’s eastern coast is wanting for river deltas now, it’s not always been so. It was an enormous braided river delta, like the Amazon or the Ganges that laid down the golden Hawkesbury sandstone, a couple of hundred metres thick, right across the Sydney Basin, 230 million years ago.

Perhaps this is an approach to marketing I can put to the NSW Tourist Board. “Volcanos! Dangerous megafauna! Epic braided river deltas! Go back far enough in time, and New South Wales has it all!!”

Reflections of North Brother Mountain on my way back to the put in at Camden Inlet

More adventures on New South Wales’ coastal lagoons

Geomorphology and dawn reflections on a midwinter lagoon at Myall and Narrabeen Lakes

A paddle across scary Lake Macquarie to see the snake-pandas of Dora Creek

Encounters with eagles on Budgewoi Lake

Moonlit night on Kylie’s Beach

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mccnmatt

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June 23, 2015

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anthropocene, Geology, History, national parks, natural history, Seasons, Soil

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Midwinter lagoon

Bombah Broadwater in the gloaming

It’s past the shortest day of the year, but, in spite of her scrapes and dings, Egg the elderly wooden kayak doesn’t seem to be ready for drydock yet. Perhaps it’s that last unseasonable whirl of autumnal warmth, caught alongside the coast in the East Australian Current, that’s keeping the sea a balmy 20 degrees. Or perhaps it’s just the lure of still, winter water all around.

Since Egg was first laid in our driveway a year ago, I’ve been seeing Sydney differently. Those long roundabout routes from A to B via M and Q and P, punctuated somewhere along the way by a bridge or two, suddenly make sense. The city of roads and buildings retreats and, I feel, just out of sight on every side, the presence of water.

The Hawkesbury estuary

Upper reaches of Berowra Creek, a hop skip and jump from the Hornsby Westfield

This is our backyard, encircled by the salty embrace of the Hawkesbury estuary. But it doesn’t end here, with the secretive topography of flooded river valleys. All the way up (and down) the New South Wales coast, the shoreline is flanked by coastal lagoons. I’m not complaining, even the tiniest little bit, about all these sheltered waters. But I’ve started to wonder what geographic accident has given a timid canoeist so much to feel grateful for.

Along with marshes and flats, coastal lagoons make up maybe 10% of the world’s seaboards, and in NSW lots of us live by them, many more than by the ocean itself. Lagoons (or wave-dominated estuaries – there are ongoing hissy-fits around these definitions) appear where low-lying plains, rather than dramatic cliffs, meet a shallow gently sloping seabed. Usually, they are found on shores shaped mainly by waves rather than big tides, with underlying rock that crumbles nicely into beach sand not finer, silty sediment.

The more sand the better – perhaps our generous continental shelf harbours this bounty from a time when the Sydney Basin was a enormous braided river delta, like the Ganges today. But you don’t want too much rain – lagoons are usually fed by an underwhelming little creek or even just groundwater – that doesn’t (or doesn’t often) burst through the land between waterway and ocean.

Dawn breaks over the barrier between Bombah Broadwater and the open sea

To make a lagoon*, you need a barrier to the open sea. In the nineteenth and first part of the twentieth century, coastal geomorphologists duked it out over just how these barriers were born. Did breaking waves make for ever-rising off-shore sand bars? Did encroaching seas submerge coastal dunes? And then there’s the third, attractively named “spit accretion theory” (Davis and Fitzgerald, 2004). Not, as it might sound, a creation myth where bunyips drool into puddles between the dunes; just sand clinging to rocky headlands as it is carried along the coast by the (delightfully piratical) longshore drift.

It turns out that everyone was right, at least some of the time. Which is nice. It’s hard to keep the heat in a scientific controversy when lots of the evidence, hidden beneath the surface of the sea in the first place, has been washed away or covered over during the last few millenia by terrestrial silt or aeolian sand. Who could be angry with such mellifluous and frankly otherworldly-sounding geomorphologies in play?

Pelican landing on Bombah Broadwater

Most lagoons have only been around for a little while, geologically speaking, formed after sea levels began to rise as glaciers melted 18,000 years ago or thereabouts. Many, like Narrabeen Lake, which we whizzed round on our bikes in the company of half the population of the North Beaches a few weeks ago, are even younger, not seven thousand years old. A blink of the eye for people who were here 50,000 years before.

Strangely, lagoons move. Today’s surfers walk across the relics of yesterday’s drowned lakes. Barrier beaches migrated landward, emerging from the ocean just as “marine transgressions” (that’s advancing oceans, not the naughtiness of waves) slowed. Shaped in stable times, coastal lakes still don’t hang around for long. This shouldn’t surprise me – I know that, despite appearances, beaches are really rivers of sand.

If the tides were higher, if the rivers was faster or siltier, if Australia wasn’t so seismically serene, the lagoons would fill up and dry out or be washed away, and the cormorants would have to hunt elsewhere. In fact, for all our dredging and draining, it’s happening right now. Like life itself, coastal lagoons are a transitory phenomenon, a passing pleasure.

Surfers floating over the relics of yesterday’s lagoon

Narrabeen Lake

Black swans in Narrabeen Lagoon

(Little?) Black cormorants

Intermediate egret in Narrabeen Lagoon

And then there’s the gyttja, something so very special it’s found nowhere else in Australia, and helps qualify Myall Lakes as a unique protected wetland. What is it? Well, rotting pondweed. No, I’m underselling it: it’s up to 70cm of “a highly mobile and organic mud that has a gelatinous appearance”, a “flocculent green–brown material” (Drew et al 2008), “an uncompacted, anoxic and sulphurous ‘ooze'” made from “the decomposition of charophytes, macrophytes, cyanobacteria and algae”. Strangely, not so much about the ooze in the National Parks brochures. But it’s an ooze that’s been there for, perhaps, a thousand years.

Dusk on Bombah Broadwater

Looking west at dawn on Bombah Broadwater

Canoeists in the gloaming

Eric the Egret on the Bombah Point Ferry

Glorious Angophora

Reflections on the tea-brown waters of Myall Lakes

Still morning on Two Mile Lake

I’ve been thinking about lies beneath the surface of the water and the windblown sand. But paddling through the Broadwater two weeks back, in a startling moment I found myself not gliding above the mysteries of quiet waterways, but surrounded, right amongst it. A huge flock, a murmuration almost, of little black cormorants, perhaps returning from a fishing trip, passed above and on one side and on the other without a single cry but with a sound I’ve never heard before: the white noise of hundreds and hundreds of moving wings.

The sound of the midwinter lagoon, all around me.

Little black cormorants murmurating

* Be warned: there’s a chance my account of the origins of coastal lagoons is completely wrong. After all, the New South Wales coast “has provoked many questions and various degrees of controversy” (Thom, 2010, 1238). And perhaps it’s “premature to attempt a comprehensive analysis of coastal lagoon evolution and dynamics when so many lagoons have been so little studied” (Bird, 1994, 13). In case you want to check my workings:

References

Bird, Erik (1994) “Physically setting and geomorphology of Coastal lagoons” in Kjerfve, B. (ed) Coastal Lagoon Processes, Elsevier
Davis, R. and Fitzgerald, D. (2004) Beaches and Coasts, Blackwell Science
Drew, Simon Iona Flett, Joanne Wilson,Henk Heijnis, C. Gregory Skilbeck (2008) “The trophic history Myall Lakes, NSW, Australia” Hydrobiologia 608
Eyre, Bradley and Damien Maher “Structure and Function of warm temperate east Australian lagoons: implications for natural and anthropogenic changes” Coastal Lagoons: Critical Habitats of Environmental Change, dited by Michael J. Kennish, Hans W. Paerl
Martin, Louis and Jose Maria Landim Dominguez (1994) “Geological history of coastal lagoons” Kjerfve, B. (ed) Coastal Lagoon Processes, Elsevier
Masselink, Gerhard and Hughes, Michael (2003) Introduction to Coastal processes and geomorphology, New York, Oxford University Press
Thom, Bruce, Hesp, Patrick, Bryant, Edward (1994) “Last glacial ‘coastal’ dunes in Eastern Australia and implications for landscape stability during the Last Glacial Maximum” Palaeogeography, Palaeoclimatology, Palaeoecology 111 (3-4)
Thom, Bruce (2010) “New South Wales” Eric Bird (ed) Encyclopaedia of the World’s Coastal Landforms, Springer

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Tag Archives: coastal lagoon

Delta bravo!

Midwinter lagoon