This is the latest in a series of articles and illustrations from our new special edition publication New Cartography.  The magazine offers readers a fresh and alternative take on mapping the urban environment through a collection of articles and illustrations from a wide array of contributors. The complete magazine can be viewed here.

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I grew up on the banks of the River Effra in South London. This is, I confess, overstated –  as one of London’s mysterious lost rivers, the Effra’s ‘banks’ are barely visible as bumps in the road, damp patches, shifts in atmosphere. Rising in the hills of Norwood, it flows underneath the streets of Dulwich and Brixton, turns sharply west at Kennington, and discharges into the Thames just south of Vauxhall Bridge, where in the Bronze Age ritual offerings of spears and shields were once made to the river gods. In a poem of 2001, at the height of my early passion, I described the Effra ‘coursing wild / from the woods’ and ‘[swilling] in drains’.

This underground urban world is again the subject of my explorations in a new project, ADRIFT, commissioned by Cape Farewell – whose work fizzes at the intersection of climate change and the arts. I am investigating not only the lost rivers, but the entire submerged landscape of London, mapping, walking and imagining ‘the city beneath the city’.

Londoners like going underground; they make 3 million journeys on the Tube every single day. Harry Beck’s diagrammatic map of the Underground, with its maze of intersecting, multicoloured lines, is a design classic: an icon of twentieth century cartography. But despite these subterranean inclinations, we know relatively little about the network of underground streams – most bricked up, many incorporated into sewers, and some completely lost – that riddle the Thames basin. Until recently, these waterways have been the preserve of antiquarians, local historians, eccentrics, dowsers, urban explorers, psychogeographers and radical poets. Such as Iain Sinclair tracing the course of the Hackney Brook and Allen Fisher channelling Nicholas Barton in his poetic explorations of the Neckinger and Effra.

The rivers pose challenges to a city increasingly concerned with flooding from tidal surges and the rising water table. When engineers burrow the foundations of skyscrapers and office blocks into the earth, they want to know the exact nature of that earth. A geotechnical survey produced in 2008 for the upgrade of Victoria Station identified a perched aquifer – a pocket of water not far under the ground – which it associated with ‘the former Tyburn River’. These phantom traces of old streams show the pervasiveness of water in the geography of London, and how futile our efforts to divert or remove it can be.

The rivers of London may mostly be lost to sight, but their legacies are embedded linguistically in street-names. The Westbourne gives us Pont Street and Bourne Terrace; the Neckinger, Brook Drive; the Tyburn,Tachbrook Street. In Battersea, Culvert Road and Heathbrook Park indicate the presence of the Heath Ditch. The Effra runs underneath Brixton Water Lane, Winterbrook Road and Effra Road. Behind Waterloo Station, Lower Marsh reminds us that Lambeth was once wetlands, only fully drained in the nineteenth century. Our prehistoric ancestors crossed these marshes using wooden causeways, and these are remembered in three streetnames: Newington Causeway, Limehouse Causeway, and The Causeway in Wandsworth. The rivers were important features of the landscape, and so they became a way of mapping and dividing up the city. Commonly, they were used as parish and then borough boundaries, so Earl’s Sluice divides Southwark from Lewisham, the Ravensbourne Lewisham from Greenwich, and so on. In prehistoric times, the significance of these streams may have been even greater – not as administrative frontiers, but as sacred loci: sites of pilgrimage, gateways to the divine realm.

Rivers are not the only features of the submerged topography of the city. London in Roman and pre-Roman times was a marshy floodplain; the Thames a wider, shallower river with multiple channels interrupted by small islands and gravel promontories. If you live somewhere with an “ee” sound at the end, like Hackney, Bermondsey, Chelsea or Battersea, then you could be on a scrap of dry land rising from the silt of the Thames; the ea or ey originating in the Old English for island.

I’m also interested in artificial or imagined islands: Fish Island in Hackney Wick, with its majestic views across the Lea Navigation to the Olympic Stadium;  Jacob’s Island at the mouth of the Neckinger, where Dickens has the villainous Bill Sykes fall to his muddy death in Oliver Twist; even the traffic islands of the Elephant & Castle interchange. My model is JG Ballard’s Concrete Island, in which an architect is marooned on wasteland between the M4 and the Westway – a motorway age Robinson Crusoe.

In a parallel world I’m a geography teacher, armed with a pair of muddy walking boots, a ragged OS map, and a bumper pack of fine-liner pens. I bought several pull-out street maps of London and started to modify them, creating eccentric palimpsests of the city. I added the rivers first in blue biro. The Effra and the Peck rising in the South, the Walbrook cutting through the City, the Fleet, the Tyburn and others, using Nicholas Barton’s classic Lost Rivers of London as my guide.

Painstakingly tracing the rivers by hand revealed fascinating convergences with the modern city. It’s alluring to see these blue biro lines wiggling their way underneath whole postcodes, then suddenly aligning with a single street, as the Fleet River does with St Pancras Way. The eye is drawn to flashpoints, points of intersection or convergence: Marble Arch, where Tyburn Gallows once marked the crossing of two Roman roads; Mount Pleasant, where the Fleet is joined by tributaries from at least two local springs; Kennington Park, where Stane Street and the Brighton Road converge and the Effra bends west over Hazard’s Bridge;Holborn Viaduct, where Watling Street crosses the Fleet and where you can still make out the valley carving down Farringdon Street.

After I’d added the lost rivers and the Roman roads to the map, I stumbled across a brilliant website by the British Geological Survey which allows you to zoom and scroll across a detailed geological map of the country. This became my next undertaking – I busted out the felt-tips and began to sketch out the geology of the city.

About two million years ago, as the Thames formed its current course after the last ice age, it dumped a variety of superficial deposits: gravels, sands and silts, and this is what I’ve represented on the map – the yellow around the river itself corresponding with its flood plain before it was embanked.

This map is my hand-drawn, multicoloured, alternative vision of the London landscape.

The process is like stripping back plaster or knocking through the stud walls of a building to expose the original structure. The facade of the modern city gives way to London Clay, Hackney Gravel, swathes of Thames alluvium, pockets of Taplow and Kempton Park Gravel, patches of brick-earth and chalk escarpments.

A vast band of South London is revealed as a marshland of mudflats, tidal inlets and freshwater creeks twisting around shallow islands. On the north bank, where the Romans founded their city, two gravel hills (Ludgate Hill and Cornhill) are bisected by the freshwater Walbrook, with London Bridge stretching across the Thames to a nodule of dry land – Southwark. The flood plains of the lost rivers are spindly fingers penetrating the interior. Thorney, where Benedictine monks first established Westminster Abbey in the tenth century, is seen here as one of three islands floating in the Tyburn delta. An inlet of Thames alluvium surrounds Battersea to the east and south, and may once have joined the River Falcon at High Tide to create a loop. Bermondsey – or ‘Beornmund’s Island’ (another Abbey site) – is finally revealed as an outcrop of Kempton Park Gravel, enclosed on three sides by wetlands, with the Peck Stream to the south and the Neckinger tracing its northern edge.

In the affluent manor of Belgravia, I discovered a dense clustering of street names – Ebury Square, Ebury Street, Ebury Bridge. When I sketched out its geology, the area emerged ghost-like from the streetmap, a gravel promontory jutting out like a crocodile’s snout into the silty confluence of three rivers. This is the village of Eia, again from the Anglo-Saxon for island, mentioned in the Doomsday Book in 1086. In the sudden marshy sprawl beyond Chelsea Bridge, where the Tyburn, Westbourne and Effra discharge into the Thames, the modern city would have been underwater: Victoria Station, Pimlico, the machinery of government. Westminster Bridge, where Wordsworth composed perhaps London’s most famous poem, would have been like a pair of scales marooned in the river, unable to reach dry land on either side. As Wordsworth’s sonnet says, ‘The river glideth at his own sweet will’.

If you really want to understand the ancient landscape of London, you have to imagine the Thames not as it is now – a single, embanked, fast-running river, but as a much wider, slower water channel with multiple courses separated by small islands – what geographers call a ‘braided river’.

To get a real sense of what a braided river might look like, I went on a day-trip upstream to Maidenhead, where the Thames is a quite different creature. There it is naturally narrower and entirely freshwater, but broken up into several channels which wind their way around tiny islands or eyots (pronounced ‘eights’),many uninhabited and, from my view on the bank at least, grown wonderfully wild with oaks and willows, spilling over their embankments into the water.

I have always been fascinated by Elephant & Castle, a much maligned area of South London best known for its Brutalist shopping centre, high-rise estates and intimidating roundabouts, around which traffic is slung like a giant pinball machine. But the Elephant was the site for perhaps the most surprising geological revelation of all.

What I already knew is that in 1641 a blacksmith named John Flaxman set up shop on an island in the area – slap bang where the modern traffic island lies.Flaxman’s forge is now the Faraday Memorial, a cuboid electricity substation I used to think was an alien spaceship as a child and where the electronic musician Aphex Twin is rumoured to have lived. What I didn’t know, but which was revealed by the geological survey, is that underneath the Elephant & Castle there lies… a peat bog.

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You can see it clearly on the British Geological Survey, and on my map – a dark grey smudge, two concentric oval pockets of alluvium and peat. Covering the ancient village of Newington, this feature is a one-of-a-kind within the London landscape. This peaty bog sitting in a deep depression in the gravel is known as the Rockingham Anomaly after the housing estate above it. Perhaps it’s a scour-hole caused by the shifting, eroding Thames after the last ice age? We don’t know for sure. It’s possible it is the collapsed remnants of a periglacial phenomenon known as a ‘pingo’. This is a volcano-shaped mound of ice that develops when water freezes and expands underneath permafrost. When the ice melts, the mound collapses, leaving a spherical depression in the earth. It reminds us that London was once a landscape of wind-blown frozen tundra.

This is all public information, but try Googling ‘Elephant & Castle’ and ‘peat bog’ and very little comes up, just a couple of archaeologists’ reports. Unsurprisingly ‘Elephant & Castle’ and ‘local depression’ yields more hits. It seems that very few people are interested in the Rockingham Anomaly, but to me it was an explosive discovery. Could this be the source of the Elephant’s strange magic, its stubborn resistance to the experiments of urban planners? Could this be why Erno Goldfinger’s pioneering high-rise Metro Central Heights suffered from Sick Building Syndrome? Why performance artist Marcus Coates chose the Elephant for his urban shamanism? Or why there is currently a group of eco-rebels establishing an urban forest in the crumbling, condemned Heygate Estate, an ‘urban lung’ for London?

I think the residents of the Elephant & Castle deserve to know that beneath their feet is a bog of peat as black and rich as that from which the prehistoric Grauballe Man was pulled; ‘bruised, like a forceps baby’ as Seamus Heaney puts it… ‘as if he had been poured in tar’.

Through creative cartography, I have begun to recover an idea of London not as a tabula rasa, but a landscape fundamentally configured by water and rock, a river basin occupied by streams and islands; an urban environment subject to natural forces. I am interested now in how my experiences of mapping and discovering obscured trails in the city might correlate with another model of walking: the pilgrimage. The lines, patterns, whole geometry of the hidden landscape suggests to me the ideal space for such a performance, a pilgrimage; a kind of communing with the world that is physical, verbal and tactile, which asserts the value of the individual human body and the relationship of that body with its environment.

A river that is long bricked up – submerged beneath the streets yet active in our place-names, in our histories, in our geology and our built environment – might  become a pathway for the new pilgrim?Might the circumference of a lost island become the route of a perambulation, a twenty-first century beating of the bounds? This vision is of impromptu roadside shrines, re-imagined vistas, street furniture as urban reliquaries, archaeology as psychology, and walking as the fulfilment of a new cartography.

Tom Chivers is a poet and literary arts producer. Author of How to Build a City (Salt, 2009) and The Terrors (Nine Arches, 2009) and several award-winning anthologies. Follow ADRIFT at http://whatisadrift.tumblr.com

The article was commissioned by The New Wolf for New Cartography – an IdeasTap-sponsored magazine.