Kathy Battista

Brandon Labelle

Barbara Penner

Steve Pile

Freelance writer, lecturer Jane Rendell

Exploring 'an area of outstanding unnatural beauty': a treasure hunt around King's Cross, London

In this paper we describe the Pleasure of treasure treasure hunt around London's King's Cross area. The pleasure of treasure was devised as a response to Richard Wentworth's exhibition An area of outstanding unnatural beauty , November 2002. Richard Wentworth sought to explore the character of King's Cross by creating an exhibition space that would provide somewhere both where the overlooked and hidden histories of King's Cross could be gathered together and also where people from the King's Cross area could engage with activities that had been lost or overlooked. Similarly, The pleasure of treasure sought to take people around the area with a view to exploring its histories and oddities. More than this, it hoped to open up the area to fresh eyes, capable of seeing the secret treasures that lay there. In keeping with Wentworth's project, the beauty of King's Cross lay not only in the process of exploration but also in the chance encounters (of various kinds) that sometimes surprise and sometimes disappoint.

In the project we came to call The pleasure of treasure , we asked people to go on a treasure hunt around King's Cross. Part search; part walk; part adventure Á/ we wanted people to explore King's Cross imaginatively, questioning what they thought they already knew about this (still) notorious area of inner-city London. The adventure of the treasure hunt. The pleasure of maps. Where was Long John Silver looking? He was after treasure Á/ pirate's gold, hidden from those who might steal it away. A cross marks the spot. King's Cross, we speculated, likely has gold buried unmarked beneath its well-trodden streets and unfamiliar passageways. But if you really watch and listen carefully, King's Cross has many other kinds of treasure, many secret pleasures. For us, the hunt itself was part of the treasure; the pleasure of exploring King's Cross in search of its hidden treasures, of discovering unexpected things about King's Cross, and perhaps finding one's own pleasures and treasures. Of course, treasure hunts also involve elements of risk, of uncertainty, and even of getting totally lost. Maps don't always lead you safely from start to finish. Integral to The pleasure of treasure was an open-endedness to the process of exploring King's Cross. In the hunt for its unexpected treasures, it's not always clear where you are, nor where you are going and, sometimes, not even when you are: at stake is where you've come from, where you're going to; what's past, what's to come.

The pleasure of treasure

The pleasure of treasure is a treasure hunt activity map created by a team of people who worked in response to an exhibition, titled An area of outstanding unnatural beauty , by the artist Richard Wentworth. This article is inspired by The pleasure of treasure project, and the ideas and discussions that instigated the treasure map as a form of urban exploration and artistic engagement. It has been written as the result of two main impulses: first and foremost, to lay out the 'back thinking' that went into the production of the treasure map and to allow these ideas to develop their own lines of thought; second, to open up the possibility that ideas such as this might have an 'afterlife', creating further possibilities for experimentation in the means and ends of urban exploration. 1 As a group, we are interested in ideas around public art, the site specificity of art and writing, and the overlapping histories that make up urban space. This article favours a discontinuous, clue-driven exploration of The pleasure of treasure , mainly because this reflects the composition of the project itself. At times, it is contradictory. At times, it doesn't add up. In places, the lines of thought run in parallel; in others, they cross at right angles. This is deliberate, since it is an accurate reflection of the treasure hunt itself, both as a map that combines many different ideas and elements, but also as an experience which different people engaged with and reacted to. We hope this will interest those who might produce similar collaborative works that engage with sitespecific public art, but also those who like an adventure with an uncertain outcome.

Waiting to explore Á/ outside 66 York Way, site of Richard Wentworth's exhibition, An area of outstanding unnatural beauty , 4 September Á/ 17 November 2002.

An area of outstanding unnatural beauty: Richard Wentworth's exhibition and the King's Cross site An area of outstanding unnatural beauty 2 was created by British artist Richard Wentworth. Organized by Artangel Á/ an agency that commissions work in unusual spaces Á/ Wentworth's project took place in the disused General Plumbing Supplies at 66 York Way in King's Cross from 4 September to 17 November 2002. The location for the exhibition was just behind King's Cross train station, in an inner-city neighbourhood of north London, and close to Richard Wentworth's home on the Caledonian Road Á/ an area that he had explored, photographed and excavated for 20 years.

The site was central to the conception of An area of outstanding unnatural beauty . As Richard Wentworth knew, the long-standing and large-scale plans for the redevelopment of the area behind King's Cross railway station were about to be implemented. 3 Private and public investment, amounting to £200 million, was set to transform the neighbourhood into 'a vibrant and successful part of a world class city', as the publicity put it. While the developer, Regent St George, is changing the physical and economic landscape of King's Cross, the local council is performing a cleansing operation that is pushing the drugs and prostitution south into Bloomsbury and north into Camden Town. In fact the King's Cross of An area of outstanding unnatural beauty is already a thing of the past: the building on York Way has been transformed into a rental car agency and the surrounding streets are almost unrecognizable in their altered, more hygienic, designer-led appearance. It is curious that a street corner once used by prostitutes and known for kerb-crawling is now under CCTV surveillance and has a Tesco metro supermarket: a change that may say much about changing patterns of consumerism in early 21st-century London!

The regeneration of King's Cross.

Instead of run-down light industry, outdated warehousing and derelict postindustrial spaces, there would be swish postmodern offices and hotels; instead of crime, there would be culture; instead of dirt and discarded needles and condoms, there would be eco-friendliness, cleanliness and happy ducks; instead of freight train depots and sidings, there would be an international rail link to Paris and the European continent beyond. Indeed, this is why the General Plumbing Stores had become vacant. For Wentworth, as much would be lost in this regeneration as gained. And his exhibition was intended to celebrate the 'lost' King's Crosses, both contemporary and past, both near and far.

Through the exhibition space, Wentworth established connections to the (about to change) neighbourhood outside. For example, the words IN and OUT were painted directly onto the floor of the entrance. The words were run together and painted in opposite directions so that it was difficult to determine which way was indeed in and which was out. Wentworth befriended the street-painters who had marked out the bus stops on York Way, and they offered to paint the words AN AREA OF OUTSTANDING UNNATURAL BEAUTY on to the floor with the same technique used on the street. The outside came in, but the inside also went out.

Inside An area of outstanding unnatural beauty . Note both the lettering on the floor and the 'ping' tables.

Once inside the site, one could climb up a staircase (in a building container placed on its end) and get a view into the street and the train station via a periscope. The exhibition also included a variety of maps of the local area that the artist had collected; videos of the street-painters, aeroplane tracks and a map-maker drawing the A Á/Z map in the traditional style; classic films that included shots of the neighbourhood; puzzles featuring the A Á/Z map; mini-A Á/Zs; and a large map where visitors stuck pins into the streets they lived on. 4 In addition, the project included a series of 'ping' tables 5 with local streets painted onto them, which were host to a local table tennis tournament of epic proportions won by the British Library's enthusiastic team.

The exhibition was distinctive in that it was clearly unspectacular, in an age where many artists are working with spectacle. It instead paid tribute to the ebb and flow of urban life and the way that people engage with the neighbourhood. Rather than make a grand statement, the artist let the participants do this through their engagement with the space, be it viewing maps, playing ping, making puzzles or looking through the periscope. Visitors would often come into the space and ask 'Where is the exhibition?', to which the reply would be: 'You're in the middle of it.' Wentworth's point is that the city itself is rich with textures that we walk over and skim past every day, and that these unclaimed layers of the city contain a history that recedes further from view with each layer that is added.

The pleasure of treasure: an engagement with Wentworth's exhibition

The pleasure of treasure was a spin-off project from An area of outstanding unnatural beauty . It was a result of pondering the following question. How does one engage with such an exhibition? Do you begin with art critics or artists or academics or other interested parties? And, in Wentworth's case, does one begin with the maps, theories of spatiality or the local politics? These were the issues that Kathy Battista dealt with on a daily basis as Head of Interaction at Artangel. 6 Kathy's role was to commission artists, writers and thinkers to engage with Artangel projects in order to create public programmes. These could be as traditional or unusual as was appropriate to each project.

For Wentworth's exhibition, Kathy was keen to involve people who would respond to the idea that the exhibition was a container for a series of fragments of the King's Cross area. This led her, initially, to a book subtitled urban fragments , edited by geographer Steve Pile. 7 Kathy and Steve met on the roof of Artangel's offices, and discussed the idea of engaging with Wentworth's exhibition without doing either a walk or a talk. With this problem now set, they decided to involve some people who they hoped would enjoy the puzzle. Those intrigued enough to join in were Jane Rendell, an art and architectural writer, Barbara Penner, an architectural historian, and Brandon LaBelle, a sound artist.

Our collaboration began by meeting in Artangel's Clerkenwell office to discuss our various interests and approaches to the problem: how to critically engage Wentworth's project, in the spirit of the exhibition, but without doing a guided tour of the area or an academic critique of the artwork. In this first meeting, we discovered a shared desire to do something 'site-specific' Á/ that is, intimately connected to King's Cross Á/ especially as we believed this to be exactly in tune with Richard Wentworth's exhibition. We therefore resolved to get to know the area in more detail. As a group we walked the King's Cross area, talked about its history and its future, and took photographs and made notes along the way. We were interested in, among other things, the architecture, literary history, overlapping geographies, people, sounds and wildlife of King's Cross. Bringing these elements together was the challenge at hand.

More meetings ensued (fuelled by pizza and red wine), and further footbound explorations of the area. At one point, partly out of frustration, one of the group came up with the idea of a scavenger hunt. Each member of the group saw that this would provide an opportunity for their interests to be explored, as well as providing a fun way to involve people in exploring the neighbourhood for themselves. Through discussion, the idea evolved into a 'treasure hunt', involving a treasure map that would guide explorers by laying a series of clues.

The pleasure of treasure was born, but it was still unformed. What would it look like? What would the clues be? How would we engage young and old? How would we keep people safe? Where would we find the maps? How would it engage people, practically and intellectually? How would it connect to Wentworth's exhibition? And, again and again, what would it look like? We decided that a map, which combined historical and contemporary features, would be a perfect starting point for people to explore and learn more about the area. We were certain that we wanted to engage people of all ages and abilities, and make a project that could be accessible and fun. So, we set out to have different levels of clues, from easy to difficult, yet also provide information about the area, drawn from many different sources.

A quick description of the maps:

. On one side, there was a contemporary map of the King's Cross neighbourhood: in part, this was to help people navigate their way around. This was also the 'clue side' of the treasure map: overlaid, around the edges of the map, we placed questions for people to answer. In effect, these guided the treasure hunters in a loose circuit that led out from, and back to, An area of outstanding unnatural beauty . . On the other side, a map from 1868 was reproduced. We chose the 1868 map particularly because it featured the Polygon building (since demolished), which was important for our trail of clues. By comparing contemporary and old maps, certain continuities and specific changes could be explored. We wanted to inaugurate a sense of times past, present and future in the King's Cross cityscape. On this side of the 'map', we also placed a series of quotes from literary works, biographies of people associated with the area, and local government and business sources to give a sense of these myriad pasts, presents and futures. 8 We worked with designer Ian Vickers in order to combine the contemporary and historical maps, as well as quotes from books set in the area, portraits of local figures (Mary Wollstonecraft, Boadicea), clues and directions. To allow all this information to be easily read, the maps were A2 in size. In order to follow the trail of clues properly, treasure hunters had to engage with both sides, each with the maps and information. The clues ranged from the creative task ('What would you build in the area marked A?') to the trivial ('Who designed the sculpture in the British Library's courtyard?').

The final goal was to collect an 'object of unnatural beauty'. The completed maps, along with these objects, were exhibited on a 'ping table' during the final weeks of Wentworth's exhibition. The range of objects collected was eclectic: from a shoe that could have been 50 years old to a toy truck, furniture legs and even bloody bandages. At the end of the exhibition, prizes for the best map, best object and best map and object were awarded. Congratulations to all who took part: we estimate about 4 500. The treasure maps on display at the exhibition.

As is traditional, the treasure hunt began with a clue. Directions took the treasureseekers to where they could find the answer. A major part of any treasure hunt is the tracking down of answers. In some ways, the maps provided a solid ground for exploring the area. Nonetheless, we wanted to defamiliarize King's Cross, to make it strange so that our hunters would look at King's Cross with new eyes . To this end, we set clues that required people to move back and forth between the present-day map and the by gone map: that is, to move back and forth in time. For example, Clue 12 asks the treasure hunters to go to Clarendon Square.

Clarendon Square used to contain The Polygon, and we asked people to find out who used to live there (we return to this site in a later clue). Today, the urban landscape contains various forms of memory of The Polygon. It exists in the heritage blue plaque that celebrates the people who lived in the site, and in the street name, Polygon Road, but also in a mural that shows what the Polygon looked like. Using both treasure maps, we asked the treasure hunters to put these surviving fragments together. In this sense, we wished not only to convey a sense of the mutability of the urban landscape Á/ that is, a sense that it is continually creating and destroying things Á/ but also to convey that, with attentiveness to the landscape, it is often possible to find fragments of the past that persist in the present.

The city is not made up of simple linear histories, which stretch from the past in smooth lines towards a vanishing point in the far-off future. Histories scrumple up, times past pop into the present, modifying them for all time. Spaces in the present wobble as stories from the future and the past shimmer in front of them. The continual turning and turning of the maps, their unfolding and folding, was part of the point: to make familiar spaces strange in time and space.

In another clue, we ask the treasure hunters to imagine a different future. For Clue 22, we blanked out an area in the contemporary map (and marked it with an A). Into this area, people drew the kind of King's Cross they would like to see: ideas ranged from boating ponds, to parks, to housing developments, to fun fairs. Very few drew King's Cross as it is likely to be. But, the point is no one knows what it actually will be like Á/ including the planners and the developers Á/ even their futures are uncertain.

Maps are not just snapshots of the present, nor chained solely to the past. Maps also fold in futures in various ways. By placing an old map and a contemporary map back to back, we not only ask questions about the past Á/ 'What happened here?' or 'How does the past survive here?' Á/ but also about the future Á/ 'What can we do with this place?'. The city is not permanently set in stone, even as it appears to be fixed and permanent. Street names jump about, disappear, reappear in other places. Roads go one way, then another, then stop, then turn around. In King's Cross as much as anywhere, this is true. Its pasts lie, it is said, interred under its roads and rails. But we also asked people to look forward. If the past demonstrates that things in the city can be moved about and changed, and if the present of King's Cross is a marked reminder that things move, disappear, appear, then it is also possible to see in the maps alternative futures.

CEGB stands for Central Electricity Generating Board, from an era when utilities such as water and electricity were publicly owned and, for all their faults, managed for the public good. CLUE 3: Along the canal, there are many benches: look at all the benches you pass, one will have a musical note nearby. The one you are looking for is near a bridge (these are marked on the map). When you find the bench sit down, staring across the canal. Very near, you will see a phone number. Call the number and wait for someone to answer. What happened? (Don't worry if you don't find the right number, we'd still like to know what happened!) 'Hello?' 'Where are you?' 'On the bus . . . What?' 'No, I'll be there in a few minutes Á/' 'I saw Barbara today . . .' 'Oh! Did you tell her about our trip?'

The phone call is a theatrical moment: the phone rings, we answer it, and a voice travels across unknown miles to arrive at our ear. Conversation unfolds in a multiplicity of modes, from the boringly professional to the deeply intimate Á/ from angry words to soft whispers. We stage our own production in the telephonic transmission of the voice whose script is written in electrical signal. To this theatre of the voice, the mobile phone adds another layer: it situates the voice, and the drama of conversation, in the public sphere, as a dynamic, annoying and empowering sound.

The mobile phone has added a distinct audible layer to sonic geography Á/ by transplanting the phone call, from the local to the global, the interior to the exterior; by making the phone mobile, it has also made speech mobile.

In addition to looking for the musical notes, pleasure seekers were requested to call a phone number found at the site of one of the notes along the canal. The number was for my mobile phone, and was painted on a wall across from a bench where the note was found. Upon calling, they would be instructed to undertake a listening exercise:

'Listen carefully to the sounds of the environment; adopt one of these sounds; try to imagine this single sound expanded over one minute; do not change it, just maintain it; try not to hum it, just think it; then quit.' CLUE 4: On leaving the canal exit (see map), walk south down Camley Street. In Camley Street, near an entrance to St Pancras churchyard, there are various information signs. Who is allowed into St Pancras mortuary?

On sunny days, the sunlight would create dappled patterns on the ground. The play of light and dark, with a slight breeze, would give you a sense of play. Something dancing in the dark, in the shadow world. King's Cross plays with the seen and the unseen. On a chilly, slightly foggy day, when London becomes shrouded in the nineteenth century, that shadow world suddenly becomes the world. King's Cross is an area of outstanding unnatural myth. Legends walk its streets, inhabit its cemeteries. Old St Pancras Church is full of such legends. Could it be that Mary Goodwin declared her love for Percy Shelley, here, over her mother's grave? Does the church lie at the centre of a magical rectangle which, the poet Aidan Andrew Dun suggests, was prophesied by Blake to demarcate the site of a New Jerusalem?

There are more tangible riddles in the churchyard. At the foot of a tree, gravestones burst from the ground. It's as if the dead have crowded around the tree. There are those that believe that spirits can gain access to the world of the living via the roots of trees. Surely this is not the purpose of this convocation of stones. The legend at the spot tells us not. Thomas Hardy saved the gravestones (and the dead and buried) when the Midland Railway Company built lines through to its new St Pancras station. If history is repeated, as Marx suggested, then is not always as tragedy first, farce second. If Hardy's actions were romantic, then today's further destruction of the churchyard Á/ as contractors lay the groundwork for the King's Cross Channel Tunnel terminal Á/ owes more to cynicism. There is no feeling for the ghosts that still inhabit the graveyard, for the love that once occurred here, for the dreams that people had for a better future Á/ only for money. Indeed, despite the brick dust and noise of heavy machinery, the whole area is taking on an air of future fortunes.

As the railway sweeps away the dead, we might not mourn. For, in earlier times, Londoners were quite happy to cover over the dirt and decay of the city. Along one bank of the church used to run the River Fleet. It's gone, replaced by a busy road. Now it's the roads that threaten the railways. The churchyard is an increasingly small no man's land between warring factions. The ghosts can only watch and despair as the living have the life choked out of them.

CLUE 7 You are in St Pancras churchyard. The grave of Sir John Soane is here. Who is buried with him?

Delving into the history of King's Cross, it is not only the physical traces that fascinate. It is also the lack of physical traces, the absences. These absences sometimes speak of the violence of the physical changes which have shaped King's Cross and continue to shape it to this day. Over time, whole sections of the area have been buried or razed to the ground, flattened to make way for urban 'improvements'.

Until now, the most notorious example was in the 1860s, when the construction of the St Pancras terminus required the removal of 3 000 tenants of Somers Town (none of whom were compensated for losing their homes). [START_REF] Stamp | From Battle Bridge to King's Cross: urban fabric and change[END_REF] Similarly, the Old St Pancras churchyard was dug up to make way for Midland Railway rail lines, an operation overseen by the young Thomas Hardy.

These frequent and brutal ruptures within the urban fabric make the history of King's Cross difficult to trace on a contemporary map. Often the only hint of what existed before lies in the blue plaques 10 which dot the area or in the street names evoking the names of past landlords, uses or buildings.

Exploring the city also means being attentive to what is no longer visible in the city: the lives of the people who resided there, or areas which have been erased. One particular life haunts the area around Old St Pancras churchyard: Mary Wollstonecraft. Author of The vindication of the rights of woman , she lived in nearby Polygon Road (which no longer exists as such) with her husband, the radical reformer William Godwin. While there, she gave birth to Mary Shelley, who would write Frankenstein . And it was here, a few days after giving birth, that Mary Wollstonecraft died, to Godwin's despair. Now, her grave rests quietly by the newly developed Eurostar railway track.

Wollstonecraft's is only one life. King's Cross is made up of much more than facts or of bricks and mortar. It is a place of histories and of stories. Many people first arrived in London here, lived here, died here; and their stories are laid out like an invisible web across the streets. These cannot be seen straight on or fully captured, but if one is paying attention, they can be momentarily glimpsed, in side-long glances, just at the edge of what remains visible. CLUE 11. What did the term 'fish' mean in 19th-century London?

Guidebooks and maps are written to be read on site. In re-entering the places they describe, these texts physically intervene in a place. In order to make critical observations, is it possible for the moment of reading to be juxtaposed with a particular site itself? Most guidebooks are not designed in this way; their form is not usually conceived of as a critical response to the social and spatial organization of the site. However a number of artists interested in guidebooks and maps have (sometimes by adopting the role of tour guide) been working in this way. [START_REF] Brennan | Prospectus: a manoeuvre[END_REF] Artists such as Tim Brennan, Janet Cardiff, Christine Hill and Marysia Lewandowska have written scripts, devised audio pieces and constructed performances that, in order to create new ways of understanding a site, make particular connections between the content and form of the writing and the place in which it is read, spoken aloud or listened to. The pleasure of treasure alludes to these art works, hoping to prompt located responses to the site.

The pleasure of treasure is somewhere between guidebook and map. The reader is provided with two maps, one old and one contemporary, and a series of quotes and clues. Map in hand, following questions, treasure seekers are offered journeys through King's Cross. In search of answers, the clues create cause for pause at one point and then another. Here, then there, treasure hunters focus on specific details in the urban fabric, important moments in the making of King's Cross, sites of future interventions, providing a change to consider the history of the area, as well as to reflect for a moment on memories of their own, allowing the site to be understood as an evolving event.

Can we call a writing that responds to a site site-specific? [START_REF]Site specificity: the ethnographic turn[END_REF] Certain genres of writing are more obviously site-specific than others. Guidebooks, for example, written in order to introduce us to a particular place, may follow a spatial logic derived from the organization of that place itself Á/ from centre to suburb, downtown to uptown. The order of material may be more closely tied to movement through a space; tour guides might use the sequence of exhibits to tell a story as the reader walks past. Maps too could be described as forms of site-specific writing. Yet they are not organized in sequence, but rather show arrangements of objects in space, offering the reader many different tours through the same place.

If certain forms of spatial layout Á/ the centralized focus of a square or the two-way traffic on a bridge-offer particular social possibilities, can the spatial forms taken by writing do likewise? If so, then the relationship that writing has to space could be far more than writing 'about' space. What about the spatial properties of writing itself? Can authors adopt imaginative, poetic and fictive constructs to build alternative positions from which to experience a place, to meet their readers? In a collection of critical essays, A. S. Byatt names works by Primo Levi, Italo Calvino and George Perec as the most interesting examples of 'topological fictions', where the term 'topological' means 'both mathematical game-playing, and narratives constructed with spatial rather with temporal images'. [START_REF] Byatt | On histories and stories[END_REF] In discussing his own interest in 'topological fictions', Calvino refers to the writings of Jorge Luis Borges and Alain Robbe-Grillet, authors who, by placing narratives inside one another, make places where it is easy to get lost. [START_REF] Calvino Refers To | Topological structures in modern literature[END_REF] In folding and unfolding the map, in reading one side and then the other, King's Cross can only be placed in an impossible position between past, present and future. To answer the clues, treasure hunters have to use their hands, eyes and imagination. [START_REF]Old St Pancras churchyard, in Dickens's A tale of two cities[END_REF] CLUE 12. Using the 1868 map, find your way to Clarendon Square (between what is now Polygon Road and Phoenix Road). Who used to live in a house on this site? When was she born? (Hint: the answer is on Werrington Street.)

In Salman Rushdie's The satanic verses , ¯it is in King's Cross that an apocalyptic uprising begins: where Gibreel Farishta, after days of dreamlike wandering, blows his trumpet and 'Babylondon' cleanses itself with flames. As rioters arm themselves and fire rains down, Gibreel reflects that London has often 'purged itself by burning', yet the choice of King's Cross as the site of this new conflagration is especially resonant. [START_REF] Rushdie | The satanic verses[END_REF] Few areas in London have been so despised; host to slums, a smallpox hospital, dust heaps, and brick-making factories in the 19th century, and a thriving trade in prostitution and drugs in the 20th. Separated from genteel Bloomsbury by the cordon sanitaire of Euston Road, the area serves as a convenient repository for the city's physical and moral dirt. [START_REF] Baeten | For discussions of how metaphors of dirt justify social segregation[END_REF] It is not by coincidence that Gibreel blows his trumpet on Goodsway as teenage prostitutes, the ultimate symbols of this dual degradation for many, come forward to kneel before him. [START_REF]Rookeries and model dwellings: English housing reform and the moralities of private space[END_REF] It is weirdly apt that Goodsway today, like the young Magdalenes, is also being offered a kind of redemption. This so-called 'suburban Sahara', this 'huge blot in the middle of . . . London', 19 is currently undergoing regeneration. The word itself is replete with the promise of cleansing, purification and renewal, so to declare 'we are ''cleaning up'' King's Cross' sounds at once like an act of house-keeping and of absolution. We should not forget that the first campaigns for urban reform intersected with the rise of Evangelicalism and remain imprinted with its moralistic mission and metaphors. 20 But we should recall, too, the words of Mishal in The satanic verses . Refusing to accept that the King's Cross riot was caused by Gibreel or his trumpet, he warns: 'What has happened here . . . is a socio-political phenomenon. Let's not fall into the trap of some damn mysticism'. 21 So there's no mistake: today's regeneration of King's Cross is driven by capitalism at its most extreme Á/ by £4 billion of private and public investment into megadevelopments such as the Channel Tunnel Rail Link. The area is now among the largest building sites in Europe and, from certain angles, is unrecognizable, hidden by giant cranes, labyrinthine road works and construction hoardings which invite the public to 'take another look' even as they cover up what lies behind. Yet, whatever their cause, the changes feel apocalyptic. Emerging from King's Cross, one is hit by the battering of drills, the fumes of bottlenecked traffic, and a flotsam of disoriented addicts and tourists tugging on wheelie luggage. Their maps are useless here .

Enduring violent assaults on its physical and social fabric has been the particular fate of King's Cross; for 200 years, whole neighbourhoods have been buried or razed to make way for urban improvements and transport infrastructure. This cycle of destruction (purging) and rebuilding (renewal) is a refugeemaker, erasing whole communities and the weave of people who lived there. The area has now become so synonymous with change and with its two great rail termini Á/ King's Cross and St Pancras Á/ that most Londoners think of it only as a place for transit and transients Á/ perpetually arriving, moving through, and departing again.

But many people have called and still call King's Cross home, including Richard Wentworth himself. Noting communities and residents, both past and present, is one aim of the pleasure of treasure project. Guiding people beyond the orbital pull of the termini, the maps and quotes underscore absences as well as the presences. Clues point to street names recalling past landlords, uses or buildings: to Polygon Road whose namesake, an eighteenth-century polygonally shaped building that was home to Mary Wollstonecraft, has long since disappeared; or to Phoenix Road, part of which has been shut off and, without apparent irony, marked 'formerly Phoenix Road'. Like so much else in King's Cross, it rests, this former road, awaiting the next blast of the trumpet to be summoned from the ashes and renewed again. The pleasure of treasure was partly forged in a discussion about the nature of treasure hunts and scavenger hunts. These are both activities normally associated with children and play. But, for us, treasure and scavenger hunts were also appealing because they revolve around objects. The treasure hunt aims to uncover objects of great value, while the scavenger hunt aims to bring together an archive of objects and information, usually worthless in a conventional sense. The treasure hunt transforms participants into seekers; the scavenger hunt, into collectors.

In this sense, each type of hunt might be said to conform to and to enact the conventions of a particular literary genre: the treasure hunt, the adventure novel, and the scavenger hunt, the detective novel. And when designing our map and constructing our clues, we initially turned to these for inspiration.

The classic detective novel, exemplified by Edgar Allan Poe, Wilkie Collins and Arthur Conan Doyle, is a distinctly urban type of fiction, set in the streets of major cities like London and Paris and revolving around cases of mistaken identity or theft, violations of privacy or the disappearance of a loved one. [START_REF] Poe | The murders in the Rue Morgue[END_REF] In contrast, the classic adventure tale, represented again by Poe and Robert Louis Stevenson, is set in exotic and remote island locales and is epic and romantic, rather than forensic, involving pirates and buried treasure, usually of gold. [START_REF] Poe | The gold bug[END_REF] Yet both types of fiction are related in that they revolve around clues and maps, and the promise that these will add up to something larger Á/ a solution, a resolution, a restoration of order, a theory, or a prize. Detective figures, like Poe's Auguste Dupin or Conan Doyle's Sherlock Holmes, counter the great Victorian fear that we can be lost or disappear in the modern city 'without a trace' (still very much a theme of popular forensic crime fantasies like Crime scene investigation). Instead, they reassure us that every person leaves some residue of their passing and of their actions on their physical surroundings: detection is a matter of being observant to details. 24 Similarly, the adventure novel depends upon the individual's powers of logic, observation and analysis. Being presented with a series of clues or directions, usually coded in cryptograms or ciphers or hidden in invisible ink, the seeker tracks down and locates treasure.

Thinking both about these genres, and about the two types of hunt, gave initial shape to our project and inspired, for instance, our request that people bring one object from their walk back to 66 York Way. Nonetheless, we realized that our reworking required almost a (con)fusing of elements; hence, the request that that the object be of 'unnatural beauty' and have 'no value', crossing the scavenger aesthetic with the treasure mode. A more general reorientation was required, too, for the world of the classic detective or adventure hunter has moved on: the transparent world of Holmes has become the opaque one of Paul Auster's Blue. [START_REF] Auster | Ghosts[END_REF] The all-encompassing solution is now elusive. The clues do not add up . The detached searcher is implicated in the action. And the search has become the story.

Asking participants to pursue object(s) or information through clues was still essential to The pleasure of treasure, but primarily as a tactic for mobilizing them, pushing them into unfamiliar terrain or terrain that becomes unfamiliar through searching. The pursuit was about activating a certain way of looking. Ernst Bloch once described the detective as having 'micrological perspective ', by which he meant that the detective sees significance in even the most trivial of details Á/ a scuff on the shoe, a particular brand of tobacco, a tyre track in the mud Á/ typically overlooked by the police or by ordinary people. [START_REF] Bloch | A philosophical view of the detective novel[END_REF] We wanted participants to navigate King's Cross in this way, seeing or hearing things which would normally be filtered out, and subjecting inconspicuous details to minute scrutiny. Where are CCTV cameras located en route ? Why is one side of Sir John Soane's mausoleum blank? This micrological perspective is similar to Wentworth's own. He asked visitors to 66 York Way to 'LOOK'. Our map asked them to take this attentiveness back with them into the streets of King's Cross. We did not promise a treasure or a solution. The pleasure was in the search. CLUE 16. Battle Bridge, which crossed the River Fleet, formerly stood on a site near the entrance to Kings Cross station. Draw on the map where you think the course of the River Fleet now runs (Hint: it's probably under your feet . . . somewhere.)

St Pancras churchyard has some strange memorials Á/ Sir John Soane's mausoleum designed by his wife, Thomas Hardy's grave Á/ as well as fascinating stories about the dust heap that used to shadow this site. But it is not possible for me to stand in the churchyard without remembering a conversation I had there one summer with environmental artists Platform. The discussion concerned the poet Aidan Andrew Dun, whose epic Vale Royal , in a manner not dissimilar to a 20th century Blake, recalls the history of the Fleet in this part of London. [START_REF] Dun | [END_REF] Dunn's King's Cross is a land of legends, ordered by sacred principles and populated by mystic figures. A concern with the spiritual aspects of the elements runs through the work of Platform, who devised a walk that traces the course of the Fleet through London, from its springing point in Hampstead, down through King's Cross and St Pancras, then on along the Farringdon Road, to the point where this tributary enters the Thames near Blackfriars Bridge.

The foul-smelling Fleet was a source of complaint as far back as the 13th century. Anxieties concerning the river's filthy condition were among the reasons given for its burial. The bottom reaches were covered over in the 17th century, and the upper reaches at the end of the nineteenth century. Today the Fleet is a sewer. When a river is buried, canalized, contained and arched over, what does it become? A sewer? Is it still a river?

At the outset of the walk, this did not seem to me such a big question. But as I walked the Fleet, my views shifted. Platform told us about a school group they had worked with as part of their campaign to uncover the buried rivers of London. When the children were told that a river lay beneath them, buried underground, they were bewildered. How? How, they had asked, do you bury a river? And, technicalities aside, why? Why would anyone want to do such a thing? Platform 9a at King's Cross station supposedly signs the body of Boadicea defeated and buried after Battlebridge. Are there any links to be made between the buried body of this ancient British queen and the burying of the river Fleet? Our present culture is one that attempts to deny the natural in so many ways; medical knowledge and technological expertise seek control of wayward human flesh as we turn a blind eye to the terrifying indications of global warming and environmental disaster around us.

I learnt so much that day. A new way of relating to London. I found out about the river as I walked it. Ley lines, song lines, story lines, some lines only speak as you walk them. Platform's walk is a meditation upon the burial of the river Fleet. [START_REF] Rendell | Imagination is the root of all change[END_REF] Standing on Platform 9a that summer we discussed King's Cross as a site still full of conflict, this time over plans for regeneration. By the time we started The pleasure of treasure, King's Cross was a construction site with no place for debate. Richard Wentworth's project and the treasure hunt we produced have been criticized for paying little heed to issues of gentrification, but it is impossible to be in King's Cross today and not be aware of the changes going on. Certainly Richard had such concerns at the heart of his interest in this part of London. When we discussed our work in the space Richard had created in the old plumbing fittings unit, the audience response made it clear: the manufacture of public consent for the redevelopment of King's Cross had not fully succeeded; there was still active resistance. One of the successes of Richard's project was the final of the 'ping' tournament held in 66 York Way between two local groups, a team of local taxi drivers and the staff of the new British Library. We listened. We looked. We touched. Sometimes, we held our noses. We searched for answers to questions. On occasion, we began to wonder whether the clues we found suggested a crime . It was as if we were tracking around a crime scene. Forensic attention to the scene would throw up more and more clues. The head of a child's toy. A packet of fags. An announcement about a train on Platform 9a. A telephone number. She loves him. He hates her. They love themselves, but hate everyone else. As we moved from answer to answer, clue to clue, we felt ourselves tracing out invisible paths. Around the area. Through the area. Movements by people, past and passed. Bodies. Motives. Opportunities. Surely there was a crime here.

We kept coming against traces that somehow amounted to more than what was before the eyes. Instead of knowing the end of the story, however, we were somehow in the middle of it. Knowing neither the motive nor the opportunity nor the victim, we had only the scene of the crime. Of course, it might be argued that there are no crimes in King's Cross, no secrets beneath the ground, no nefarious goings-on. The grimy needles, the colourful condoms Á/ merely innocent detritus. King's Cross has its reputation to keep. But here we were, detectives with no crime. A map with no treasure. But in turning King's Cross into a crime scene without a crime, we were inviting people to imagine that what had happened here was not just, or fair, or even true.

We turned to Boadicea for help (Clues 17 and 18), famed as an English queen who put the invading Romans to the sword. Merciless slaughterer of Romans, but also slaughtered by them. There's murder in the air. Murder. And motive. Boadicea has a reputation for fighting against injustice, so the fact she lies dead beneath a railway track might cause us to remember those who have died on railways tracks: too many of late, and surely the killing is not over. It gave us further pause for thought on the 'regeneration' of King's Cross, and in whose name the creative destruction of the area was taking place. Not Boadicea. Clues there are, and answers few and far between. No one takes responsibility, of course, so it is up to those who examine King's Cross in detail to worry about the crimes, to worry about the scene and to wonder Á/ even if everything is innocent on the surface Á/ whether there isn't a crime waiting to be discovered, exhumed, brought to light.

Our walks around King's Cross traced out a body like chalk marks around the victim: that of King's Cross itself. Many people traced out their own King's Cross, their own bodies. Body. Motive. Opportunity. We are not imagining it. King's Cross is a crime scene. CLUE 23. Now you're in Kings Cross station, go to Platform 1. There, search for the musical note Á / it is somewhere before the end and after the beginning, closer to your feet than your eyes. When you find the note stand directly on it. Close your eyes. What can you hear?

The chiming of a bicycle bell, the flapping of a shopping bag caught in a tree branch . . .

In approaching

The pleasure of treasure , I was interested to insert sound into the overall process of how one 'reads' the city: looking for clues, following maps, hoping for signs, all function through processes of reading, which are in turn based on looking. How then to lead a participant to 'look' for sound? In response, I painted musical notes on sites around Kings Cross that I found particularly rich in aural attributes, such as the Kings Cross train station, along the canal, and at a crosswalk at the intersection of Pentonville Road and York Way. Through the map and its clues, pleasure seekers were asked to look for the musical notes, and once found, to stop and listen, or undertake certain actions. What was heard in a sense functioned as referent to the clue */ that is, it was essentially the answer.

Train announcements indecipherably echoing . . . Through such a performative process it was imagined that one would be brought through the alphabetical (reading, looking) and into the acoustical and the ephemeral yet persistent presence of sound. As a paradigm, the acoustical can be defined by shifting the interpretive act away from an 'alphabetical' approach (reading) and toward a non-representational one (listening). [START_REF] Fiumara | The other side of language: a philosophy of listening[END_REF] For the acoustical complicates or extends experience, perception and understanding by adding or subtracting their fixity . To further delineate the acoustical, we can initially define it in contrast to the alphabetical and its emphasis on visuality, representation and language. The alphabetical governs and directs perception and cognition through a literate emphasis on text and symbolic codes. In contrast, the acoustical as a paradigm replaces visuality with listening, representation with radiophony, and language with orality. Such contrasting redirects our view of the world, and ultimate understanding of it, from the symbolic, as representational systems lexically functioning as referential, to the experiential arena of the real.

Such a dichotomy runs the risk of separating the alphabetical from the acoustical to a point of opposition, whereby the acoustical functions as the alphabetical's 'other'. It should therefore be emphasized that the two are continually overlapping, invading each other; that is to say, their relationship rather than their opposition contributes to the definition of both, outside any moral perspective of one being 'better' than the other. Yet the acoustical is an underdeveloped theoretical framework, as can be understood in western civilization's predisposition to the alphabetical Á/ to sign systems and a dominant belief that 'seeing is believing'. To follow the acoustical is to pose an ontological and epistemological shift, for, as musicologist Robin Maconie suggests, 'unlike visual experience. . . which unfolds in front of and under control of the viewer and tends to be articulated from moment to moment, episodically, the listening experience is continuous, ever-present, and unavoidable, and by comparison less susceptible to direct control'. [START_REF] Maconie | The concept of music[END_REF] Inserting the acoustical into the cartographic field thus complicates the very notion of understanding a city, as a whole. The construction of any map obfuscates the reality of social space Á/ through aerial perspective, reduced scale, machinic graphic rendering, a map is an abstracted space that positions the 'reader' as omnipotent viewer. The pleasure of treasure ruptured such reading by producing a map that was multiple, experiential and participatory. Through the presence of the historical past, made manifest in the reproduction of a map of the area from 1868 */ and the immediate present through encouraging pleasure seekers to 'perform' the map: imagining their own fantasy of a future King's Cross, drawing on the map, hunting for clues whose answers were to be found through an experience of the city */ and through the insertion of sound into cartography, the discrepancies between maps and their cities, between reading and the actual, are cause for jouissance.

The lapping of water, the clamorous drone of trains . . . Working with sound as an artistic medium, I have been led to a consideration of geography: from sound it seems 'place' soon follows, and the presence of architecture and social space. For sound brings into relief spatial dynamics, from acoustical elements (resonance, decay, vibration) to ecological features (aural environments, noise pollution, biodiversity). Sound can thus be heard as a layer within the environment, a form, however ephemeral, of information that may tell us something about where we are, a 'sonic geography' whose properties reside in the invisible fluctuations of air.

Distant rustling of leaves, faint clucking of ducks . . .

To shift from the eye to the ear as governing perceptual and epistemological locus is to underscore the 'sociality' of sonic ecologies Á/ the boisterous crowd, music in the park, traffic as a parade of noise, all such events exceed their respective limits because by nature sound is always expanding and thereby articulating a different set of borders, beyond the literate, to the side of representation, within the field of interaction. To make a sound then is to always make a public gesture.

LAST CLUE: Whose pictures are printed overleaf?

Recent disappointments with some of the non-critical object-sculptures produced as 'public art' have resulted in a certain scepticism concerning what objects can do, and preference instead for process-based work. But I wonder whether we should reject objects outright. Beyond a discussion of their visual surfaces, their formal qualities, their technical expertises, objects have important roles to play. In mediating between real and imaginary spaces, objects can provide possibilities for people to communicate dreams and desires through material forms, and to bring the potentially transformational power of the imagination into sharp focus.

Through such psychic processes as identification, introjection and projection, psychoanalytic theories explore the complex relationships between people and objects. Object relations theory, created and developed by the Independent British Analysts, focuses precisely on the unconscious relationship that exists between a subject and his/her objects, both internal and external. [START_REF] Kohon | The British School of Psychoanalysis: the independent tradition[END_REF] Donald Winnicott introduced the idea of a transitional object, related to, but distinct from, both the external object (the mother's breast) and the internal object (the introjected breast). [START_REF] Winnicott | Transitional objects and transitional phenomena[END_REF] For Winnicott, the transitional object implied an ability to make a distinction between fantasy and fact and to keep inner and outer realities separate yet inter-related. Winnicott claimed that this intermediate area of experience was retained from childhood, and later in life contributed to the intensity of experiences around art and religion.

Christopher Bollas, who took certain aspects of Winnicott's work further, emphazised the mother as process rather than as object, and focused on her important function as provider of the child's 'environment'. [START_REF] Bollas | The transformational object[END_REF] In constantly altering the infant's environment to meet his/her needs, Bollas argued that the mother was experienced as transformation. Bollas suggested that in creating the 'transformational object', the transformational process was displaced from the mother environment onto 'subjective-objects'. Bollas linked this first creative act to aesthetic experience, describing the 'aesthetic moment' as one where an individual feels a 'deep subjective rapport with an object'. 34 According to Bollas, the uncanny feeling of fusion we experience with some objects is a recollection of the earlier feeling of being transformed.

In her research into language with eight-year-old Italian children, French feminist philosopher Luce Irigaray has described how, when given a preposition to use, girls made sentences that linked them to people, whereas boys made sentences that linked them to objects. Irigaray's speculates that this female desire to form relationships with others can provide the starting point for imagining new forms of relationship between men and women.

Far from wanting to possess you in linking myself to you, I preserve a 'to', a safeguard of the in-direction between us Á/ I Love to You , and not: I love you. This 'to' safeguards a place of transcendence between us, a place of respect which is both obligated and desired, a place of possible alliance. [START_REF] Irigaray | To be two[END_REF] Irigaray's insertion of the word 'to' into the phrase 'I love you' indicates a new social order of relations between two equal yet different sexes. Prepositions like 'to' possess strongly suggestive roles, allowing us to think more specifically about how we construct relationships between subjects and objects. As philosopher Michel Serres has observed, prepositions have the potential to change everything around them. [START_REF] Serres | Angels: a modern myth[END_REF] Such theoretical perspectives suggest that objects, both real and imaginary, mediate inner and outer worlds producing powerful aesthetic experiences and feelings of transformation. The treasure the seekers brought us did just this. A shabby old shoe, a plastic toy, a rusty hub cap and bloody bandage, all came to the old plumbing fittings warehouse in King's Cross possessed by extraordinary powers: to tell us stories about their past lives to allow us to imagine to bridge the worlds between us to encourage play and speculation to challenge capitalist notions of profit and ownership to suggest potential future uses to demand new forms of action and like prepositions, to make unexpected connections changing everything around them . . . GENERAL QUESTION: As you carry out your treasure hunt, look out for an object of unnatural beauty. We would like you to deposit your found object at 66 York Way (General Plumbing Supplies). It should be an object of no value and not belong to anyone. Briefly describe the object in the space below.

Treasure hunters brought in many objects of unnatural beauty in response to The pleasure of treasure. These began to accumulate in a corner of 66 York Way on storage shelves which had formerly held plumbing supplies. An old, holey shoe. A broken sex education videotape (found in a schoolyard). A hubcap. Some bloodied bandages. A small plastic red and green truck.

Later, these objects were spread out on a ping table in an impromptu display. Many visitors stooped over to take a closer look, intrigued by the display of damaged and soiled treasure. Though the objects were of 'no value' (a condition stipulated in our instructions), they had been momentarily elevated above junk status as a result of being retrieved by the treasure hunters, removed from their habitual context and exhibited.

Maybe it was the feeling that these objects had somehow been salvaged Á/ redemption again Á/ that led one person to express concern about them. She worried that they were 'unloved' and asked what would become of them after the installation was packed away. In truth, we had not given it much thought. The point to us had always seemed to lie in the now; in people seeing something normally classified as rubbish and finding beauty in it, an exercise that not coincidentally paralleled Wentworth's own photographic practice. [START_REF]See Wentworth's photographs of objects on the Caledonian Road, King's Cross. R. Wentworth[END_REF] Recognizing that this reversal was fleeting, however, we thought the most appropriate afterlife for our objects would be to throw them away.

But we held off and, at the end of the exhibition, ended up instead gathering up the treasure into several shopping bags, as if holding them in trust for a future work.

We did not wait long. Shortly after 66 York Way closed, we received a communication via the geographer Jill Fenton from a French surrealist, Jean-Pierre Le Goff, whose small-scale urban interventions involve careful juxtapositions of text, object and image. [START_REF] Pivaro | Le cachet de la poste[END_REF] He wanted our red and green truck for an intervention, 'Sortie de camions', on rue des Couronnes in Paris. [START_REF]For more on the intervention 'Sortie de camions[END_REF] So the little truck went on a grand tour: we sent it to Paris to become part of Jean-Pierre's work, before Jean-Pierre himself eventually brought the truck back with him to London.

21 September 2003. Some members of The pleasure of treasure group and some members of Jean-Pierre's Surrealist group meet on the corner between St Pancras station and King's Cross. On a large piece of white construction paper and in a childlike scrawl, Jean-Pierre has written a poetic text describing the journey of the red and green truck back and forth across the Channel. It suddenly strikes us, standing on the site of the future Channel Tunnel terminus, how appropriate it is that this is the spot where our circuit of gifting and exchange will end.

Jean-Pierre attaches his text to a blue construction hoarding behind us. He removes the little red and green truck from a bag and places it beneath the text. Rushing between St Pancras and King's Cross, people look curiously at us Á/ a semi-circle of well-dressed people standing still, eyes pressed against digital cameras, photographing what? A few stop. They clock the truck, the hand written sign Á/ what kind of shrine is this? Á/ and, heads shaking or smiling, move along again.

We linger for a while, before deciding we are too conspicuous. Casting back the odd glance, we drift away, leaving our fetishes to their own defences. Within minutes a homeless man, moving swiftly, scoops up the truck. He does not break stride. He does not glance down. Some of us follow him down the street and see him place the truck on a small outcropping of St. Pancras Station just a few blocks away. An animated debate ensues about randomness, accident and chance. Our homeless man was wearing red and green. Some see this as coincidence; others as part of a larger pattern of signification.

The green and red truck crosses and recrosses the channel; Jean Pierre Le Goff ( J. P. L. G.) links the truck to the channel tunnel.

The truck is 'found' by someone wearing green and red.

CLUE 1 :

 1 Walk North from 66 York Way. From York Way, you can access the canal towing path (see map). As you walk the canal path, look out for the letters CEGB Á / what do these mean? What does the warning say?

CLUE 15 .

 15 Someone has chased you from the British Library, and they're shouting 'Stop! Murderer!!'. You've run breathless into St Pancras Station.They're close behind you, and closing in Á / not a second to spare. Quick . . .

  what are you going to do? (Give details below.)

CLUE 18 .

 18 Was Boadicea killed: (a) by the Romans; (b) by her own hand; (c) by her own warriors; (d) by Jarvis, the contractors responsible for maintenance on railway lines out of King's Cross?

Kathy Battista, Brandon LaBelle, Barbara Penner, Steve Pile and Jane Rendell

Exploring 'an area of outstanding unnatural beauty'. . .

Acknowledgements

We would like to thank the following for participating in this project: three anonymous referees, Ben Campkin, Phil Crang, Jill Fenton, Michael Morris, Catherine Nash, Jean-Pierre Le Goff, James Lingwood, David Pinder, Charles Rice and Richard Wentworth.

Jean-Pierre indicates it is time for lunch. Over the meal, we raise our glasses and make a toast. To the red and green truck, wherever it is. To King's Cross.

Finding the object: the green and red truck. 4 Our awareness that Richard Wentworth intended to make a great deal of maps and mapmaking in his exhibition was one of the inspirations for the treasure map. For us, this accorded with more academic interpretations of mapping that seek to uncover maps' relationship to place, power and even subjectivity. See e.g. D. Cosgrove, ed., Mappings (London, Reaktion, 1998); P. Gould and R. White, Mental maps (London, Routledge, 1974); P. Jackson, Maps of meaning: an introduction to cultural geography (London, Unwin Hyman, 1989); S. Pile and N. Thrift, eds, Mapping the subject: geographies of cultural transformation (London, Routledge, 1995); and D. Wood, The power of maps (London, Routledge, 1992). 5 Richard Wentworth insisted on calling 'ping-pong' just 'ping'. The idea for including the table tennis tables and tournament in the exhibition came from his sense that this had once been a popular activity for locals and was now no longer available. 6 Artangel is perhaps most famous for commissioning Rachel Whiteread's House (1993).

Artangel is committed to commissioning new work that is not only exceptional but also uses unusual 'quasi-public' spaces. In this way, it hopes to change expectations of art as well as influence debates about art and public space. 7 In fact the subtitle was later removed, and the book is only called City A Á/Z (see n. 1 for details). 8 Some of this material was drawn from websites, including www.camden.gov.uk; www.kingscrosslondon.com; www.findagrave.com; www.stpancrasoldchurch.org.uk; and, www.kingscrosslondon.com.


S Munier
email: simon.munier@cemagref.fr.

G Belaud
email: belaud@msem.univ-montp2.fr.

X Litrico
email: xavier.litrico@cemagref.fr.

Closed-form Expression of the Response-Time of an Open-Channel

Keywords: Open channel flow, Analytical model, Response time, Flow control, Canal design

Computing accurately the response time of an open-channel is of extreme importance for management operations on canal networks, such as feed-forward control problems. The methods proposed in the literature to approximate the response time do not always account for the influence of a cross-structure at the downstream end of a canal pool, which may have a significant impact on the response time. This paper proposes a new approach to compute the response time, accounting explicitly for the backwater and the feedback effects due to the downstream cross structure. The method provides a distributed analytical expression of the response time as a function of the characteristics of the canal (geometry, roughness) and of the downstream cross structure. A test canal with a weir or a gate at the downstream end is used to compare the new method with some others. Results show that the proposed expression accurately reproduces the response time for various backwater and downstream boundary conditions.

Introduction

The response time of an irrigation canal or a regulated river is usually defined as the time required for the system to transit from an initial steady state to a final steady state Fig. 1. Delay time and rising time for a step input. [START_REF] Ankum | Flow Control in Irrigation and Drainage[END_REF]. The time can be a few hours in medium-size canals or a few days in large canals or rivers and it depends on the discharge and water depth all along the canal pool. It is key information for managers, especially when they have to release water into the system so as to achieve pre-specified distribution schedules, which is called open-loop control.

The notion of response time is not clearly defined in the literature. In the following, the response time for a step input is defined as the sum of two terms: the delay time and the rising time (see Fig. 1). The delay time is the time at which the discharge increase is observed at the downstream end of the canal. The rising time is defined as the time required for the discharge to reach α % of the maximum discharge increase. In this paper, the response time at α % is denoted T (α) .

A standard approach is to approximate the response time to a step input by the time T ΔV necessary to supply a volume ΔV of the dynamic storage, defined by the volume variation between the initial and the final steady state [START_REF] Schuurmans | Analytical formulae for the response time of irrigation canals[END_REF][START_REF] Burt | Water delivery control[END_REF].

As pointed out by [START_REF] Ankum | Flow Control in Irrigation and Drainage[END_REF], this definition leads to underestimating the response time as it ignores the fact that the outflow increases with the storage and the wave travel time is neglected. [START_REF] Schuurmans | Analytical formulae for the response time of irrigation canals[END_REF] improved this estimation by coupling the discharge and the water depth at the downstream end of the reach. This allowed him to compute an approximate expression of the response time at α %, denoted T (α)

Sch in the following. The approximation performs well for short canals, which can be assumed to behave as storage basins. [START_REF] Schuurmans | Analytical formulae for the response time of irrigation canals[END_REF] uses the diffusive wave equation diffusion effects in long canals. [START_REF] Ankum | Flow Control in Irrigation and Drainage[END_REF] proposed a simple method to estimate the response time at 100 %, denoted T Ank in the following, considering that T (50) is close to the mean of T (0) and T (100) . T (0) corresponds to the delay time, which is the time T DW required for the dynamic waves to travel through the canal. T DW is obtained by:

T DW = x C + V (1)
where x is the distance along the canal, V is the mean flow velocity, C = gA/T the wave celerity with g the gravitational acceleration, A the wetted area and T the top width. The author assumed that T (50) is equal to T ΔV , which leads to the following expression of the response time:

T Ank = 2T ΔV -T DW (2)
Although these estimates give quick indicators for the canal response, it is useful to define the response time more accurately, namely by considering the effects of a cross structure at the downstream end of the reach. [START_REF] Schuurmans | Open-channel flow model approximation for controller design[END_REF] adopted a frequency approach to establish the transfer function of a reach in uniform flow. To account for the downstream cross structures, they assumed that the backwater part behaved as a reservoir, in which the water level is horizontal. Their model was able to correctly reproduce a step inflow on two canals with backwater curves.

Based on their method, [START_REF] Bautista | Computerized anticipatory control of irrigation delivery systems[END_REF] proposed an improved estimation of the canal dynamics by taking the travel time in the backwater part into account. For the two example canals used later in this paper, the results obtained by [START_REF] Bautista | Computerized anticipatory control of irrigation delivery systems[END_REF] are very similar to those obtained using the dynamic storage approximation (T ΔV ), despite a theoretically more accurate estimation of the response time. In the following, only T ΔV will be represented. [START_REF] Strelkoff | Influence of canal geometry and dynamics on controllability[END_REF] studied the influence of the downstream boundary condition with different hydraulic structures at the downstream end of the canal. The steady state regime was considered non-uniform. They used a numerical model to estimate the response to a step inflow. They showed that not only the downstream water depth (and the backwater curve) had an influence on the flow dynamics, but also the nature of the hydraulic structure at the downstream end (feedback effect).

The backwater effect can be considered as a static effect due to a cross structure at the downstream end, whereas the feedback effect may be considered as a dynamic effect due to the local relation between downstream discharge and water depth variations. Some of the previous methods to estimate the response time take the backwater effect into account by considering a backwater part where the flow dynamics is modified. But none of them accounts for the feedback effect, which may lead to important under-or overestimation of the response time as shown further.

Following the idea of [START_REF] Schuurmans | Open-channel flow model approximation for controller design[END_REF] and Litrico andFromion (2004b), Munier et al. (2008) proposed a linear model, called LBLR for Linear Backwater Lag and Route, that considered separately backwater and feedback effects, both evaluated using the equation characterizing the downstream cross structure. The model was obtained by approximating the frequency response of a canal (Litrico and Fromion 2004a) and allowed the authors to calculate the response at any abscissa along the canal, which gave satisfactory results compared to full Saint-Venant's numerical solutions. This paper aims at proposing a closedform expression of the response time, derived from the LBLR model. The proposed formula explicitly accounts for the backwater and feedback effects due to the downstream boundary condition. Illustrations are given for different boundary conditions, for simulated and real data. Some design applications are proposed.

Analytical calculation of the response time

We first derive the LBLR moel, before illustrating the results on a test canal.

Calculation of the response time using the LBLR model

We consider a trapezoidal prismatic channel. Time and distance are denoted t and x respectively, the discharge Q and the water depth Y are functions of (x, t). The equations of the flow dynamics are linearized around a non uniform reference regime defined by Q 0 and Y 0 (x) (see Fig. 2). Small variations in discharge and water depth are denoted q(x, t) and y(x, t) respectively. At the cross structure, the discharge is related to the water depth using the discharge equation:

Q(X, t) = f (Y (X, t)) (3)
In the following, Eqs. (4-5) are used to describe a weir and a gate respectively.

Q = 2gC w L w (Y -Z w ) 3/2 (4) Q = 2gC g L g W g √ Y (5)
where L w is the weir length, Z w the sill elevation, L g the gate length, W g the gate opening, C w and C g some discharge coefficients. The discharge equation is used to determine the downstream water depth Y X = Y 0 (X) corresponding to the reference discharge Q 0 . In addition, the linearization of Eq. (3) leads to:

q(X, t) = ky(X, t) (6)
where k = df dY is the feedback coefficient. One may

obtain k = 3 2 Q 0 Y X -Zw for a weir and k = 1 2 Q 0 Y X
for a gate. The downstream boundary condition is then given by the couple (Y X , k).

In the method developed by [START_REF] Munier | Distributed approximation of open-channel flow routing accounting for backwater effects[END_REF], the transfer function between the upstream discharge and the discharge at any location in the channel is approximated by a first-order-with-delay transfer function using the moment matching method. The backwater

Q +q(0,t) Q +q(x,t) x Y (0)+y(0,t) Y (X)+y(X,t) 0 Q +q(X,t) 0 0 0 0 0 X Fig. 2. General scheme of the considered channel.
effects are taken into account by decomposing the canal into two sub-pools and the feedback effects are represented by k. This leads to an analytical expression of the response to a step input at any location:

q(x, t) = 1 -e -t-τ (x) K(x) (7)
where τ (x) and K(x) are obtained as closed-form expressions of the physical parameters of the pool (geometry, friction, reference discharge) and of the downstream boundary condition (downstream water depth and feedback coefficient). Appendix I describes how the transfer function is evaluated and approximated. Details of the calculation of τ (x) and K(x) are

given in appendix II.

The delay time is given by τ (x), whereas the rising time only depends on K(x). According to Eq. ( 7), the response time

T (α)
LBLR is given by:

T (α) LBLR (x) = τ (x) -K(x) log 1 - α 100 (8)
The LBLR model has been implemented under the free software Scilab (www.scilab.org)

and the files needed to compute the response time

T (α)
LBLR are available on request.

Application to a test canal

In order to compare the different methods of response time calculation, we use the test canal proposed by [START_REF] Strelkoff | Influence of canal geometry and dynamics on controllability[END_REF]. The characteristics of the test canal are presented in Table 1.

The test canal considered here is rectangular (bank slope m = 0) but the analytical ex-

X B m S b n Y n 1.9 m 3 /s 2300 m
2 m 0 0.00044 0.014 sm -1/3 1.00 m pression of the response time presented further includes the case of a trapezoidal canal. The reference step response is calculated using SIC, a software that discretizes the Saint-Venant equations using a Preissmann scheme [START_REF] Strelkoff | Influence of canal geometry and dynamics on controllability[END_REF][START_REF] Baume | SIC: a 1D hydrodynamic model for river and irrigation canal modeling and regulation[END_REF]). In the following, the time step and the space step are chosen in order to ensure an accurate simulation Step response with a gate at the downstream end.

Computation of the response time with the different methods

The response time for the test canal has been calculated using the different methods presented in the review section. Figs. 5 and6 show, for the weir and for the gate respectively, the evolution of the response time with respect to α, calculated using SIC or the LBLR model.

The LBLR method leads to a very good approximation of T (α) for all values of α. It is able to accurately account for backwater and feedback effects. Here, the relative error of

T (90) LBLR compared to T (90)
SIC is only 11 % for the weir and 16 % for the gate.

The response times calculated with the other methods (T DW , T ΔV , T Ank , T

Sch ) are also represented on Fig. 5 and6. As [START_REF] Ankum | Flow Control in Irrigation and Drainage[END_REF] suggested, we assume that T DW and T ΔV correspond to α = 0 and α = 50 respectively.

The method developed by [START_REF] Schuurmans | Analytical formulae for the response time of irrigation canals[END_REF], which does not account for the feedback effects, provides quite good results for the weir, but not for the gate. Indeed, a variation in the upstream discharge implies a smaller variation in the downstream water depth for the weir than for the gate. This is due to the fact that the feedback coefficient k is larger in the case of the weir, which provides a better control of the downstream level.

These graphs also show that T DW is quite the same in both cases and is suitable to estimate T (0) . Besides, T ΔV varies a lot between both cases, but remains close to T (50) . In fact, the method to compute T ΔV uses the volume variation between the initial and final steady states. This requires the calculation of the water depth variation induced by the discharge variation, which is related to the feedback effect. As a consequence, in this method, the backwater and the feedback effects are taken into account. For these two methods, the relative error is greater than 20 % for one or both downstream boundary conditions considered.

The response time along the channel reach

It is often useful to know the response time not only at the downstream end of the channel, but also at any intermediate position. The test canal has been used to compute the response time at 90 % using the different methods and for different intermediate positions.

Validation on real data

The LBLR method is now validated on a real canal. The reach considered here is 4.9 km long. It is part of the Gignac canal, located north west of Montpellier. The design profile of the canal is prismatic, which was verified in 2000 by a field survey with 191 cross sections.

The bottom slope is 0.000244 m/m, the bottom width is 0.73 m and the bank slope is 0.93 m/m. The Manning coefficient is 0.025, which corresponds to a rough concrete surface.

A gate at the upstream end of the reach allows the control of upstream discharge. A weir is located at the downstream end. It is 10 m long and 1.1 m high.

The simulated event is a flow release of 100 L/s in October 2008 for an experiment described in [START_REF] Rabbani | Flatness-based control of open-channel flow in an irrigation canal using SCADA[END_REF]. The monitoring time step is 5 min. The graph on the left in Fig. 9 shows the response at the downstream end to a step input. The solid line represents a fitted curve used to estimate the real response time.

Fig. 9. Field measurements and response time approximation

The graph on the right shows the response time T (α) with respect to α. Measurements are compared with two approximations based on the LBLR method. For both approximations, characteristics of the equivalent canal are used. The first approximation assumes no downstream boundary condition (classical case of a semi-infinite channel) and the second one uses the characteristics of the weir to evaluate the downstream boundary condition.

Results clearly show that the LBLR method provides an accurate estimation of the response time of an open-channel. Besides, the weir at the downstream end significantly modifies the dynamics by introducing backwater and feedback effects. The LBLR model is able to take these effects into account.

Design Application

Effects of the downstream boundary condition on the response time

A design application is now presented. Considering the example canal described in Table 1, we analyze how the response time is affected by the weir length, the sill elevation or the gate opening. In this case, both Y X and k may vary. This application provides a tool which may help the designer to fix the characteristics of the downstream structure according to response time objectives. For instance, let us consider a weir at the downstream end (Fig. 10). Changing its length (points W, A and B) has an effect on the backwater and on the feedback. However, the effect on the response time is rather limited (T (90) *

LBLR varies from about 0.6 to 0.9). On the contrary, if the sill elevation is doubled (point C to D), the response time is divided by 2. Concerning the gate (Fig. 11), increasing the opening (point F to E) leads to a significant decrease of the response time.

One may also remark that each modification of the cross structure characteristics has a different impact on the flow dynamics. For instance, an increase of the downstream water depth (and then of the volume of the reach) can be obtained by increasing the sill elevation (C to D), by decreasing the weir length (W to B) or by decreasing the gate opening (E to F). Yet, in the first case (C to D), the response time decreases, whereas it increases in the two other cases (W to B and E to F). Consequently, considering only the evolution of the downstream water depth is not sufficient to predict the evolution of the response time. It is essential to take the feedback effect into account, as well as the backwater effect.

Influence of the reference discharge

The last presented application concerns operation on irrigation canals. For management purposes, it is common to maintain the downstream water level at a specified value, which may be done by manipulating a gate at the downstream end of the reach.

In this application, the previous canal is considered with a gate at the downstream end.

The downstream water depth is set to 1 m, which is the normal depth corresponding to a discharge of 1.9 m 3 /s. Then, we decrease the reference discharge from 1.9 m 3 /s to 0.5 m 3 /s. The gate opening is calculated for each discharge in order to maintain Y X equal to 1 m. Fig. 12 represents the backwater curves for the different reference discharges. The method presented previously is then used to compute the response time at 90 % for each discharge (see Fig. 13). T DW and T ΔV are also represented for comparison.

Results show that the response time may vary a lot according to the reference discharge. This kind of graph may be directly used for manual operations on an irrigation canal, in order to manage upstream releases according to the flow conditions and to the characteristics of the hydraulic cross structure.

Conclusions

This paper proposed a clarified description of the response-time of an irrigation canal.

In particular, the difference between the response time, the travel time and the rising time has been pointed out. We presented a new method to estimate the response time. It is based on a physical approximation of the flow dynamics and allows to compute quickly the response time anywhere in the channel. The method takes the effects of a downstream cross structure into account, including the feedback effects as well as the backwater effects. It has been shown in this paper that both effects may have a large impact on the response time.

This new method can be used for feed-forward control problems, or for canal network management. For instance, it may help the canal designer to choose suitable characteristics of the downstream hydraulic structure according to the management objectives, when expressed as constraints on the response time. Finally, the method allows the manager of an irrigation canal to quickly estimate the response time according the reference discharge when a local controller is used to maintain the downstream water depth at a specified value.

Notation

The following symbols are used in this paper: q(x, s) = T F (x, s)q(0, s)

where the Laplace variable is denoted s.

The backwater approximation consists in decomposing the channel into two sub-pools: a uniform part upstream and a backwater part downstream, designated by subscripts 1 and 2 respectively. The backwater curve is approximated by a straight line in each sub-pool. The abscissa of the separation between the two parts is denoted X 1 and defined as shown on Fig.

14. The slope S X of the backwater curve at the downstream end is given by:

S X = dY dx X = S b -S fX 1 -F 2 X ( 10
)
where S fX is the friction slope and F X the Froude number, calculated at the downstream end of the reach (x = X).

The downstream boundary condition is given by the couple (Y X , k), where Y X is the downstream water depth and k the feedback coefficient. The decomposition is determined using the characteristics of the channel and Y X , and leads to the length X i and the mean water depth Y i for each sub-pool (i = 1, 2). Knowing Y i , each of the following variables can be computed for each sub-pool: T i , P i , A i , V i , C i and κ i , i = 1, 2, where T is the top width (m), P the wetted perimeter (m), A the wetted area (m 2 ), V = Q 0 /A the mean velocity (ms -1 ), C = gA/T the wave celerity and κ is a parameter defined as below:

κ = 7 3 - 4 3 A T P ∂P ∂Y (11)
We define, for i = 1, 2:

λ i1 = a i + b i s -a 2 i + 2a i c i s + (2a i d i + c 2 i )s 2 (12) λ i2 = a i + b i s + a 2 i + 2a i c i s + (2a i d i + c 2 i )s 2 (13) with a i = gS b (1+κ i ) 2(C 2 i -V 2 i ) , b i = V i C 2 i -V 2 i , c i = V i C 2 i -V 2 i + 2 V i (1+κ i ) , d i = 1 2a i C 2 i (C 2 i -V 2 i ) 2 -c 2 i .
We also define:

ρ i = k i λ i1 + T i s k i λ i2 + T i s (14)
with k 1 = -T 2 s 1-ρ 2 e (λ 21 -λ 22 )X 2 λ 21 -λ 22 ρ 2 e (λ 21 -λ 22 )X 2 and k 2 = k. Under these assumptions and given the upstream discharge, the discharge at any position can be obtained using the Saint-Venant transfer function:

T F (x, s) = ⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩ 1-ρ 1 e (λ 11 -λ 12 )(X 1 -x)
1-ρ 1 e (λ 11 -λ 12 )X 1 e λ 11 x if x ≤ X 1

(1-ρ 1 )e λ 11 X 1 1-ρ 1 e (λ 11 -λ 12 )X 1 1-ρ 2 e (λ 21 -λ 22 )(X 2 -(x-X 1 ))

1-ρ 2 e (λ 21 -λ 22 )X 2 e λ 21 (x-X 1 ) if x > X 1

(15)

The expression of the Saint-Venant transfer function is generally too complex to be easily inverted back to the time domain explicitly, so an approximation is required to get the response in the time domain. To that purpose, the classical moment matching method [START_REF] Dooge | Properties of the generalized downstream channel response[END_REF][START_REF] Munier | Distributed approximation of open-channel flow routing accounting for backwater effects[END_REF]) is used to derive an approximate first-order-with-delay model for flow routing (Eq. ( 16)).

T F (x, s) = G(x)e -τ (x)s 1 + K(x)s (16)

The purpose of the moment matching method is to match the moments of the exact transfer function T F (x, s) to those of the approximate one T F (x, s), which ensures a good representation for the low frequency range. To obtain the first three moments of the exact transfer function, the Taylor series expansion of T F (x, s) is first computed, leading to:

T F (x, s) = A(x) + B(x)s + C(x)s 2 + o(s 2 ) ( 17
)
Details of the computation are given in appendix II.

One may note that, according to the continuity equation, the coefficient A(x) is equal to unity, which leads to G(x) = 1.

Then the moment matching method leads to the following system: This method provides a low frequency approximation of the flow transfer and leads to an analytical and distributed expression of the model parameters. The time delay τ (x) and the time constant K(x) are obtained as analytical functions of the feedback coefficient k and the physical parameters of the pool (geometry, friction, discharge, downstream water depth).

K(x) = 2C (
According to Eq. ( 16), the output q(x, t) for a step input is: q(x, t) = (1e -t-τ (x) K(x) ) (20)

This expression allows us to easily compute the response time.

  Fig. 3.Step response with a weir at the downstream end.

Fig. 5 .Fig. 6 .

 56 Fig. 5. Response time at α % with respect to α, with a weir at the downstream end.

Fig. 7 .

 7 Fig. 7. Response time at 90 % all along the channel with a weir at the downstream end.

Figs. 7 Fig. 8 .

 78 Figs.7 and 8show the results with the weir and the gate respectively.Among the tested methods, the LBLR model is clearly the most accurate in terms of response time estimation all along the channel and for all values of α. The calculation of T Ank is able to reproduce the evolution of T (90) SIC all along the channel, but with less accuracy

Fig. 10 Fig. 10 .

 1010 Fig. 10 and 11 show the relative response time at 90 % T (90) * LBLR with respect to the relative downstream water depth (Y * X = Y X /Y n ) and the relative feedback (k * = k/k n ). k n can be calculated using the Manning equation that describes a uniform flow. For each downstream boundary condition (Y X , k), T(90)LBLR is normalized by the response time at 90 % corresponding to (Y n , k n ). Consequently, the uniform flow corresponds to Y * X = 1 and k * = 1; at this point,

Fig. 11 .

 11 Fig. 11. Relative response time at 90% with respect to the relative downstream water depth Y * X and the relative feedback k * with a gate at the downstream end.

Fig. 13 .

 13 Fig. 12. Backwater curve for the different discharges.

A

  Fig. 14. Canal pool decomposition: uniform and backwater parts for the backwater curve approximation.

  x) -B(x) 2 (18) τ (x) = -B(x) -2C(x) -B(x) 2 (19)

Table 1 . Characteristics of the test canal.

 1

	Reference Length Width Bank Bottom	Manning	Normal
	discharge	slope	slope	coefficient	depth
	Q 0

Author-produced version of the article published in Journal of Irrigation and Drainage Engineering, 2010, Volume 136, Issue 10, pp. 677-684. The original publication is available at http://ascelibrary.aip.org/iro/ doi: 10.1061/(ASCE)IR.1943-4774.0000241

Acknowledgments

This work was jointly supported by Region Languedoc Roussillon and Cemagref within the PhD thesis of Simon Munier, under the supervision of X. Litrico and G. Belaud.

Author-produced version of the article published in Journal of Irrigation and Drainage Engineering, 2010, Volume 136, Issue 10, pp. 677-684. The original publication is available at http://ascelibrary.aip.org/iro/ doi: 10.1061/(ASCE) IR.1943-4774.0000241

Appendix II. Taylor Series of the Saint-Venant Transfer Function

The moment matching method is used to approximate the transfer function by a firstorder-plus-delay. To apply this method, we compute the Taylor series of the transfer function.

For each sub-pool (i = 1..2), we define Z i (x) and T F i0 (x) as following:

The two parameters τ (x) and K(x) of the first-order-with-delay are obtained by: