I am old, I am unfit for this project and I am colder than hell frozen over but I am also stuck. A helicopter will not winch me out because my only injuries are the agonies of dodgy hips, screaming arm muscles and deeply wounded pride.

And there are miles and days to go before I sleep again on a mattress with clean sheets and a pillow and luxuriate in a hot shower and can be propelled forward in ways that do not require the use of my arms.

But I am stubborn too. And I have wanted to be here on the Franklin River for so long. In 1982, in the midst of the angry campaign to stop the damming of the Tasmanian river, my father took me to see Bob Brown talk. He screened a film about the river and I was captivated.

I was a teenager, barely grown out of the free-range childhood I’d spent scrambling around the creek below my family home on the edge of the range in Toowoomba, Queensland, following it to a sheer-drop waterfall, maybe 10 metres high, which I scaled in bare feet. My kingdom: the moss and lichen and ferns, the tadpoles, the bowerbird’s nest. I whispered into tree hollows (too much Enid Blyton), climbed trees and jealously guarded the location of a secret cave.

But somewhere along the way I lost myself. I forgot the moss and the ferns. High school, university, city living, holidays in foreign cities, years spent wearing a silly degree of pretence and affectation.

I still hadn’t found myself when an image of a misty stretch of the Franklin River flashed past me on social media. I emailed the rafting company to ask if middle-aged women with average (really, less than) fitness and no paddling skills could join its eight-day group journey down a river famous for its perilous, roaring white water. Why yes, they said. With barely a thought I clicked “confirm payment”.

‘While our guides tell stories of the merciless water … I do not dwell on them.’ Photograph: Stephanie Wood

And so here I am, pre-dawn, day two, shivering and entombed in a sleeping bag on a thin foam pad on a sandy patch of a pebbled river beach beside a fallen Huon pine with a stranger snoring nearby. As the sun rises and I drag on my wetsuit I see the shape of my body indented in the sand and think, in a day, a week or a month, the river will rise and my form will be erased.

“Who do you think is older, you or me?” the snoring stranger asks and I am affronted because of course he is, with his thatch of grey hair and wispy white tendrils poking up around his neck from his dry suit and his tall tales of retirement adventures. But it is quickly apparent that he is immeasurably fitter than me and practised at identifying good campsites and stringing tarps between trees. As the days go on, he expands into his strength and confidence and maleness while, in the privacy of my own thoughts, I struggle.

But I am persistent and will not be defeated. I learn there is a fine line between fear and thrill: I had dreaded most the drops on the river, those few moments when a raft goes over an edge and briefly is near-vertical before it rights itself again. But those moments turn out to be intoxicating, a fun park ride. And while our guides tell stories of the merciless water and its seething cauldrons and deep holes that can catch a person and pull them under or trap a man’s leg in a vice-like grip for days until the leg must be removed and he is half dead, I do not dwell on them.

‘But as we collaborate to negotiate the Franklin’s wilderness … I find myself too.’ Photograph: Stephanie Wood

The more difficult things are my private battles: my overloaded pack (because you never know what you might need, do you?) and the cliff that must be scaled along the river’s edge carrying that pack while our guides manoeuvre the rafts over patches of low-water. The exhausting days when we are in and out of the raft, helping to portage them through dangerous or shallow sections: “One, two, three, pull!” The indignity of my Michelin man appearance. The mortification when I tumble from the raft into a logjammed whirlpool at the bottom of a drop and the guide grabs me by my lifejacket straps and hauls me back in.

But as we collaborate to negotiate the Franklin’s wilderness, “Nasty Notch” and “the Great Ravine”, “the Corkscrew” and “Deception Gorge”, I find myself too. In the knowledge that strength of mind can be as valuable as strength of body. Beating on, a boat against the current.

And new thoughts are occurring to me, new possibilities apparent. I know now that I have the strength for almost anything, for expeditions I had not previously considered: treks in Alaska or through wild Canadian forests, pilgrimage walks across Japan, adventures in Costa Rican rainforests. Or to search for what matters: streams tumbling over stones in rainforested gullies, mist layered on a river at dawn, the water’s roar over boulders the size of houses, towering trees born during the Roman empire, eagles dipping and soaring, moss and lichen and ferns.