"A great many must be walking over England nowadays for the primary object of writing books," wrote Edward Thomas, who spent the years immediately before the first world war doing just that. "It has not been decided whether this is a worthy object," he added with characteristic wryness. From the 1920s onwards, metropolitan taste-makers were in general agreement that of all literary genres, the English Journey was among the least worthy of serious consideration. It belonged with the occasional essay and the countryman's nature notes as an epitome of all that was middlebrow, provincial and reactionary.

Edward Thomas made the remark early in The Icknield Way, a classic example of the genre, structured around a 10-day walk across middle England, with diversions into the highways and byways of literary anecdote, folklore, natural history and the passing conversation of stout, red-faced salt-of-the-earth types. In the second half of the 20th century, volumes of this kind languished by the barrow-load outside the second-hand bookshops on Charing Cross Road. To the young writer seeking to earn her spurs  let alone to publishers and literary agents  nothing would have seemed more quixotic, indeed retrograde, than the composition of a highly personal and digressive account of a ramble on a long-distance footpath or a walk along the riverbank.

Something changed just before the turn of the millennium, in large measure as a result of the late flowering of three extraordinary writers born at the back end of the second world war. Iain Sinclair's Lights Out For the Territory (1997) reinvented the walking book as a postmodern collage of psychogeography, dirty realism and romantic nostalgia for a lost Albion. WG Sebald's The Rings of Saturn (1998) showed that if you had a distinctive literary voice you could hold together personal memory, minute observation and obscure learning in the form of a journey through a landscape that to ordinary eyes seemed humdrum. And Roger Deakin's Waterlog (1999) substituted river for road in a wild swim through the watery sources of Englishness. The example of Sinbaldkin, as we might christen the trio, has shaped the prose of a new generation of non-fiction writers from Robert Macfarlane and Mark Cocker to (with a more cosmopolitan twist) Philip Hoare and Edmund de Waal.

To the River, Olivia Laing's debut book, follows the River Ouse in Sussex just as Edward Thomas followed the Icknield Way, but she manages her account very much in the manner of Sinbaldkin. She has an eye for a floating leaf and an ear for the intrusion of ugly modernity in a pub car park. She wanders from classical mythology to the Venerable Bede's sparrow to an acute paragraph of literary criticism concerning the multiple meanings of the word "incapable" in Gertrude's description of the drowned Ophelia.

The Sussex Ouse draws Laing because it is the river by which Virginia Woolf lived and in which she drowned herself in 1941. The book's project is to use the river to enter the stream of Woolf's consciousness and to follow in her literary wake. The pages about her last novel, Between the Acts, are exceptionally well done. There is something very male about the Sinbaldkin output, and it is to Laing's credit that she succeeds in feminising the genre.

That said, there are clear dangers in being Sinbaldkin's daughter. The temptation to over-write, for a start: "a scurf of petals drifting idly along the bank"  an editor could have blue-pencilled that idle "idly". And then the desire to include every last bit of obscure knowledge: there is a logic to the progression from the riverbank to The Wind in the Willows to the death of Kenneth Grahame's son, but do we really need to know that another Edwardian Sussex man of letters, EV Lucas, owned a formidable stash of pornography as well as editing the works of Charles Lamb? There is a certain predictability to the whole thing: once the historical lore starts accumulating, you just know that sooner or later Piltdown Man will come lumbering over the hill. And, inevitably, the book, like the river, ends by going into the blue with Derek Jarman at Dungeness.

The genre is ripe for parody, but that is only a sign of how well it has re-established itself.

Jonathan Bate's books include The Song of the Earth.

In one of his short essays, GK Chesterton describes taking coloured chalks and brown paper up on to the Sussex Downs to do some sketching. Partway into a portrayal of a herd of cows, he realises, to his annoyance, he has forgotten to bring any white. He mopes around in a sort of despair, before suddenly realising: he is sitting on "an immense warehouse of white chalk". Problem solved. He breaks off a piece of the rock underfoot, and he's away.

A kind of desire to draw with, and be drawn by, the landscape informs Olivia Laing's first book. In 2009, a series of minor crises led Laing to the Ouse in Sussex. The river  like all rivers  has magnetic properties, and a reassuring sense of direction that appeals to those who've "lost faith with where they're headed". More than its geographical, material facts or its winding blue filament on an OS map, it provides a metaphor for time's eddy and flow, and for memory.

History hasn't crossed paths with the Ouse very often, and if we only know one thing about this river, it's likely to be that it was where Virginia Woolf drowned herself  wearing Wellington boots, fastening on her hat and filling her jacket pockets with heavy stones  in March 1941. Laing was aware of Woolf as soon as she first dipped her hand in the Ouse a decade ago, and began returning for walks and swims that "amassed the weight of ritual". Laing and the Ouse have history.

With Woolf as a presiding spirit, she undertakes to walk this 42-mile, ten-a-penny kind of English river that rises near Haywards Heath and empties into the Channel at Newhaven (City of the Dead, according to Woolf) from source to sea. Significantly, she chooses a week at midsummer, the year's hinge. The journey she records here feels like a clearing and a clarifying, bringing to mind the old Latin tag solvitur ambulando: literally, sorting it out by walking. She immerses herself in the landscape; she achieves that trance-like state "when the feet and the blood seem to collide and harmonise" that's conducive to writing.

And the writing, at its best, is wonderfully allusive  a golden cloud of summer pollen is as fecund and generative as the wind Plato thought could impregnate horses  and precise, often finding all manner of surprising likenesses: dragonflies "the size of kitchen matches" cruise the air; cut grass is baled in blue plastic "the exact colour of surgical scrubs". The book's subject and structure fuse pleasingly, weaving and meandering, changing pace and tone, pooling into biographical, mythical or historical backwaters before picking up the thread of Laing's riparian journey again.

It's easy to lose grip  one digression leads from Laing's anxieties about entering the maze of a wood into a childhood memory of listening to a story tape of The Wind in the Willows in her father's car, before entering the troubled waters of Kenneth Grahame's life  but overall it seems a course worth taking. A chapter centred on the barons' war of the 13th century weaves together several channels of thought and inquiry deftly, and ends with a lovely, galvanising confluence: the Hastings train passing over the compacted bones of the men who fought at the Battle of Lewes in 1264, set in chalk downs built from the slow accumulation of the plates and shells of tiny marine animals.

It's hard not to warm to Laing, a self-confessed obsessive hydrophiliac, as a guide. She packs a slab of emergency cheese that sweats worryingly over the course of her weeklong walk. She is candidly nervous around cows, in the mazy isolation of woods, on a road leading through peeling terraced housing. She might start missing her eyeliner. She gets lost, and gives her rucksack a good kicking.

Laing values her river walk less for its social dimensions than as an opportunity for solitude and reflection. The past falls open unexpectedly, and its wider accretions and effacements  the lost forest of Andredesleage, the iguanodon bones Gideon Mantell discovered in the Wealden sandstone, the Piltdown Man forgery a century later  loom over the landscape she walks through. Often, the people she encounters are italicised noises-off. These irruptions serve to heighten the sense of Laing's absorption, and the scale of her thought, but run the risk of her sounding a little rarefied: a shame since her reading of Woolf's diaries, letters and unpublished work here goes some way to debunking similar, routine assumptions about that writer.

Woolf was one of those authors whose "paper rivers" formed the origin of Laing's watery obsessions, and there's an intriguing correspondence between "sources": rooting in "a copse of hazel and stunted oak" to find the indefinite "clammy runnel" of the Ouse, and shuffling among original manuscripts in a bone-dry archive. The subsequent journey to the sea is shaded by existential doubt but lit by what Laing the walker finds at her feet. Another writer who walked in Sussex, John Cowper Powys, experienced similar moments of delirious happiness over a century ago, the simple ability to bear witness being "sufficient reward for having been born upon this cruelty-blasted planet!" We find our happiness on this Earth, or not at all, and the Ouse, tricked from its course, poisoned and abstracted, flows implacably on. It's a bigger, deeper river on paper now, and we might say Laing has put it on the map; but allowed to slip free of our grid references feels truer, and more affirmative.

Paul Farley is a poet and co-author of Edgelands