PUBLISHED FOR THE VENICE IN PERIL FUND: THE BRITISH … · OF SAVING VENICE PUBLISHED FOR THE VENICE IN PERIL FUND: THE BRITISH COMMITTEE FOR THE PRESERVATION OF VENICE One hundred

THE SCIENCEOF SAVING VENICE

PUBLISHED FOR THE VENICE IN PERIL FUND:

THE BRITISH COMMITTEE FOR THE PRESERVATION

OF VENICE

www.veniceinperil.org

One hundred years ago, St Mark’s Square flooded

less than 10 times a year; since 2000, this has hap-

pened over 60 times a year. Venice is also at risk of

being disastrously flooded if there is another strong

storm surge in the Adriatic Sea, as in 1966. And

then there is climate change, which poses one of

the biggest threats to the survival of Venice in the

next 100 years, global average sea level could rise

by at least 8cm and as much as 88cm. Many of the

natural dynamics of lagoon processes that have

shaped and maintained the city for centuries and

made the Venice lagoon one of the Mediterranean’s

most precious wetlands are threatened by wide-

spread degradation.

This book is the distillation of the current state of

scientific knowledge about the nature and causes of

the threat to Venice, and about proposed solutions.

It is the fruit of a three-year research project based at

Cambridge University, and a conference held there

in 2003 that was attended by over 130 scientists

from around the world. CORILA was the project’s

Venice partner.

BY CAROLINE FLETCHER AND JANE DA MOSTO

THESCIENCE

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Dr Caroline Fletcher BSc Chemistry (Birmingham University); MSc EnvironmentalTechnology and PhD Civil Engineering (Imperial College,London). Ten years consultancy at HR Wallingford Ltd, special-ising in pollution, estuary processes, sediments and port developments for projects in Europe, USA, Middle East and Far East. Main research interests include the impact of humanactivities on the coastal environment,especially balancing theirrelation to natural processes in marine systems. Elected to theVenice in Peril Fellowship (Churchill College) in collaborationwith the Department of Geography,University of Cambridge.

Jane da MostoMA Zoology (Oxford University); MSc Environmental Tech-nology (Imperial College, London).Research has spread fromenvironmental valuation and social accounting (FondazioneEni Enrico Mattei, Milan) to strengthening the links betweenscience and policy in the area of sustainable development viaprojects supported by the European Commission.Coordina-tor of the Scientific Committee for Local Agenda 21 (Comunedi Venezia), carried out census of global change research forthe Italian branch of the International Geosphere BiosphereProgramme. Selected as local counterpart for VIP ResearchFellowship at CORILA (Consortium for the Coordination ofResearch Activities Concerning the Venice Lagoon System).

THE SCIENCE OF SAVING VENICE

BY CAROLINE FLETCHER AND JANE DA MOSTO

PUBLISHED FOR THE VENICE IN PERIL FUND:THE BRITISH COMMITTEE FOR THEPRESERVATION OF VENICE

www.veniceinperil.org

THE SCIENCE OF SAVING VENICE

6 Foreword

8 CRISIS

16 SETTING18 City in the marshes20 Profile of the lagoon22 A history of intervention24 Lagoon to sea26 Ecological impacts

30 FLOODING32 Why does Venice flood?34 Sinking city, rising seas40 Flooding more frequently42 City under attack

44 REMEDIES46 Defending the city48 Repairing and renewing the city50 Rescuing St Mark’s Square52 Protecting the lagoon54 Revitalising the saltmarshes56 Experiments in restoring saltmarsh58 Measures at the coast

60 BARRIER62 The mobile barriers64 How will the barriers work?66 Learning from other schemes70 Debates about the barrier72 A summary of interventions

74 FUTURES76 Venice and global warming 78 Science and uncertainty80 What future does Venice want?83 Venice must be saved

84 Organisations and legal framework88 Glossary90 Picture credits91 Index

ConsultantDeirdre Janson-Smith Science communication consultantand writer. Graduated in zoology from Edinburgh University.Trained first in the award-winning exhibition developmentdepartment at the Natural History Museum in London.Consultancy work includes projects with many majormuseums, science centres and zoos throughout the world.Writes on science, medicine and history.

PhotographerSarah Quill Creator of a unique photographic record of the city’s architecture, environment and daily life, havingworked in Venice for many years.The collection has become akey resource for publishers and scholars.

The Venice in Peril Fund thanks the major supportersof this book and the research project at Cambridge The J. Paul Getty TrustPizza Express plcMarina Morrisson AtwaterThe Headley TrustThe Boston Chapter of Save Venice Inc.Sir Mark and Lady Moody-Stuart

AcknowledgementsAppreciation to all the dedicated scientists whose work has formed the basis of this book, many of whomgenerously spent time discussing their work with us.Tom Spencer, Pierpaolo Campostrini and Frances,Lady Clarke have provided valuable guidance throughout.Sincere thanks to Deirdre, Steve, Ray and Ian and staff atCORILA who have made the book possible.

Contents

Published 2004 by Umberto Allemandi e C.Via Mancini 8Turin 10131ItalyT +39 011 819 91 11F +39 011 819 30 90

[email protected]

Copyright © 2004 The Venice in Peril Fund

All rights reserved. No part of this publication maybe reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy,recording or any information retrieval system, withoutpermission in writing from the publisher.

ISBN 88-422 1310-1

Printed in Italy by CAST,Turin

Edited by Steven SwabyDesigned by Price Watkins, London

Cover: The great flood of 4 November 1966Endpapers:The lagoon in the 16th century (after Cristoforo Sabbadino)Satellite view of the same in the 20th century Frontspiece: St Mark’s Square

For the children of Venice – present and future

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THE 16 million visitors who come to Venice annuallysee restoration going on everywhere. This is a citywhere property values are booming and monumentsare expertly guarded by the Superintendencies, the

responsible government officials. But the deeper reality is lesshappy. Time is running out for this loveliest of cities. The fre-quency of flooding is increasing, and Venice is essentially nobetter protected from an extreme weather event than it was atthe time of the great flood in 1966.

The arguments over whether mobile barriers between thelagoon and the Adriatic are necessary or actually damaginghave divided the citizens of Venice and Italian politicians intocamps so fiercely opposed that one is reminded of the Mon-tagues and Capulets. The moderate have held back fromdiscussions, not knowing where the truth lies. Vital protectivemeasures have certainly been delayed by at least a decade, andcomprehensive long-term planning, which Venice needs to thesame degree as The Netherlands, has languished.

The science contained in this book presents a timely distillation of current research and potential solutions. Venice

in Peril hopes that those who have the power to take decisionsabout the future of Venice will feel that they now can do so onthe basis of more certain knowledge.

This book reveals that the great majority of scientistsbelieve Venice must have some sort of mobile barrier to protectit from extreme flooding events, but it also makes clear howmany other factors are threatening the lagoon, and why the ecologists are right to be seriously worried about its health. Venice cannot be saved without investment in both:barrier and lagoon. To ask people to choose between them is afalse dichotomy.

Above all, this book shows that scientists will be crucial tothe future of Venice. Italy has for years under-invested inresearch in all areas of life, and people are beginning to realisehow much this threatens the country’s place in the world. Sci-ence for Venice is one of those areas. If we want ourgreat-grandchildren to see this incomparable achievement ofman, we have to accept that there is no final solution to itsproblems. It will always be work in progress and it will alwaysbe expensive – but it is a price worth paying.

Anna Somers CocksChairman, Venice in Peril

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Crisis“Oh Venice! Oh Venice! When thy marble walls

Are level with the waters, there shall beA cry of nations o’er thy sunken halls,A loud lament along the sweeping sea!”

George Byron, Ode On Venice

left Venetians face the aftermath of the disastrous flood of 4 November 1966

1CENTURIES ago, on each Ascension Day, the Doges of Venice wouldperform a ceremony called ‘the marriage to the sea’. Dropping aconsecrated ring into the waters of the Venetian lagoon, theydeclared, ‘Desponsamus te mare’ – ‘We wed thee, Sea’. Today, cityand sea are still as intimately bound together as ever. But theirs is a

marriage in crisis. The first real wake-up call for Venice came on the fateful night of 3 Novem-

ber, 1966, when a violent storm surge from the Adriatic swept over the city,flooding it to nearly 2m above normal water level in its labyrinthine canals, andleft it with no electricity, black oil oozing out of the cisterns, and alleywaysstrewn with rubbish and the corpses of pigeons and rats. The flood threw aharsh spotlight onto the crumbling city, which was slowly but surely sinkinginto the waters of the lagoon that gave it life.

THE ‘VENICE PROBLEM’The ‘Venice problem’ was quickly declared to be of national interest and a pri-ority for action. Italy has since enacted several laws to safeguard the city andlagoon, and a great deal of restoration and protection work against floodinghas, and is, being done. This is largely financed by the government (asdescribed in the Appendix). But Venice suffers from far more than flooding,and the task of solving the city’s many problems is an extremely difficult one.Scientific and political debates about what to do to protect the city and

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THE NEED FOR INFORMED DIALOGUEThe message from the 2003 Cambridge conferenceis clear. Most participants agree that the threat ofglobal sea level rise means that Venice’s only hopefor the future is to be able to block out the Adriaticwhen the need arises – although the barriers areconsidered neither a final, nor a sole, solution tothe city’s woes. Without more well-founded andintegrated analyses of the complex scientific issuesinvolved, an appreciation that there is much moreto know and a greater willingness to collaborate

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lagoon are also part of its history – the mostrecent considerations of flood protection beganover 30 years ago, culminating in a decision inDecember 2001 to move forward with an ambi-tious co-ordinated series of flood protection andrestoration projects. Its centrepiece, given a cau-tious go-ahead in April 2003, is a vast mobilebarrier system stretching across the three inletsto the lagoon. Its purpose: to block out the Adri-atic Sea during extreme storms, isolating thelagoon from the surging floodwaters.

Opposition to this grand, highly experimen-tal scheme remains fierce, primarily on thegrounds that it could destroy the lagoon’s alreadydamaged ecosystem, and that it fails to addressmany other urgent threats to the long-term sus-tainability of the city. The heat of debatesurrounding its planning and development tendsto drown out the more complex and subtle argu-ments about how to protect and restore Veniceand its lagoon. But the future of both can neverbe assured unless the choices made to safeguardthem are based on sound science.

DRAWING TOGETHER THE EXPERTISEIn 2001, Venice in Peril funded research at Cam-bridge University’s Coastal Research Unit and atCORILA, the Venice-based consortium for coor-dinating research concerning the lagoon system.The aim was to bring together reliable researchfrom the many groups and laboratories workingin Venice for an international review of the state of knowledge.

The charity, which traditionally funds archi-tectural restoration, cultural and artistic projects,had realised that there would be little point inrescuing individual buildings while the wholecity remained under increasing threat from flood-ing. A much wider perspective was needed.

The aim of both the project and the meeting itinspired (see An International Conference on page11) has been to establish a sound basis of under-standing, drawing together the multiple sourcesof information from many disciplines, often iso-lated from each other, so that a holistic picture ofproblems facing Venice – and their possible solu-tions – could emerge. The ability of experts toshare knowledge and experiences is of huge ben-efit, not only to Venice, but also to other placesfacing the same issues in managing sensitivecoastal wetlands.

Venice was founded inadversity, in the middle of a lagoon yet this broughtextraordinary advantages –from reed huts on stilts,the settlement developedinto a maritimesuperpower and splendidcity. The interventions ofman throughout Venice’shistory have focused onmaintaining the symbioticrelationship between thecity and its lagoon. Now, atthe beginning of the 21stcentury,Venice’s survival isthreatened by:above Fragility of itscrumbling architecturalheritageabove, left Floodingwhich has become achronic affliction left Risks to the efficient running ofemergency services

above, right Ecosystemdegradation and loss ofthe functions that gavelife to Venice right Scientists areworking to address the growing number of challenges to the city’s survival

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openly, sharing both problems and solutions,Venice’s future looks very uncertain.

Venetians, and the millions of tourists whocome to visit this World Heritage city, strugglethrough winter floodwaters with increasing regu-larity, past abandoned and decaying buildings.Rising waters and a disappearing ecosystem areaccelerating the decline. Global warming threat-ens its future.

The research effort is immense, with hun-dreds of experts working on the problem from allover Italy and the world. Their work is vital inhelping the many stakeholders to make their deci-sions about the future of Venice. The chapters that follow aim to summarise the state of scientificand technical research at the start of the 21st century, explaining what is known about the cityand lagoon, what is still open to debate and fur-ther study, and how scientific expertise caninform policy for Venice in the future. While thereis still much more to be learned in the nextdecades of this century, solutons are requirednow, and fast.

AN INTERNATIONAL CONFERENCE

FOR decades, scientists and engineers havebeen studying the dynamics of the lagoon andcity, trying to understand how the two interact,what is happening to them today, and howflood protection and other measures mightimpact on them. Despite the huge amount ofresearch conducted over the years, there is stilla great deal that is not fully understood.Additionally, past studies often suffered from alack of coordination and their findings lackedeffective dissemination.

To instigate an informed debate about thecity and lagoon across a wide range ofdisciplines, a four-day international conferencewas held in September 2003 at CambridgeUniversity, England, and hosted by ChurchillCollege. Instigated and supported by the Venicein Peril Fund, the conference invited around130 scientists, engineers and other stakeholdersfrom Italy and around the world – the firsttime such an international gathering had beenheld since UNESCO called experts together in1969 in response to the 1966 Venice flood.

The scientific and technical papers of themeeting are being published by CambridgeUniversity Press in a peer-reviewed book,Flooding and Environmental Challenges for Veniceand its Lagoon: State of Knowledge.

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Summary of conclusions

SETTING

■ Venice lagoon is a rich and semi-natural ecosystem,inextricably linked to the life of the historic city and aunique ecosystem within the Mediterranean panorama

■ The lagoon emerged 4–6,000 years ago and 1,000 yearsof human actions and interventions have had aprofound effect on its physical structure and ecology

■ Today, the lagoon is at risk of becoming a marine bay,due to erosion of sediments and stronger waterexchanges with the Adriatic Sea

■ As the water deepens, the city is more vulnerable toflooding and associated urban decay

■ Vital lagoon habitats have already been lost and thosethat remain are under threat – and with them, thenatural dynamics that the city depends on

FLOODING

■ Flooding is caused primarily by storm surges –winds that drive water into the lagoon

■ Many man-made changes have inadvertentlyreduced the lagoon’s resistance to incomingwaters, against a background of sea level rise – hence higher tides

■ It is not a new phenomenon for Venice, but the damaging effects of flooding create aninsatiable demand for urban maintenance andare gradually driving the population away

■ The idea that Venice is sinking comes from theextraction of groundwater in the mid-20thcentury, which caused major land subsidence.This has now been stopped and Venice hasreturned to subsiding naturally and gradually

■ Barriers at the inlets will protect Venice fromextreme water levels; other measures arebeing taken to protect the city from medium-high tides and ‘chronic’ flooding

BARRIER

■ To protect against extreme flooding, construction hasbegun for the MOSE scheme of mobile barriers andbreakwaters at the lagoon inlets

■ Further measures are needed to reverse thedegradation of the lagoon system, to complement andmitigate the negative impacts of the barrier system

■ Venice can benefit from experience gained in reducingflood risk in other places, notably flexibility duringimplementation, institutional rigour and unexpectedbenefits/adaptations of the system

■ This is a new phase for science in Venice, where someold questions are sharpened by implementation of thebarriers and many new questions arise

■ The long-term options for Venice will need to beconsidered in the context of uncertainty over futureglobal environmental change

REMEDIES

■ All projects to restore the lagoon and protectthe city must work in a symbiotic way

■ There are two kinds of measures:‘local’measures within the city and the islands,and ‘diffuse’ measures across the entire lagoon environment

■ Local measures offer vital opportunities toimprove the city’s infrastructure and restore its buildings

■ Some remedial measures are highlyexperimental and their effects will only belearned in the long-term

■ Restoring the saltmarshes is key to the futurehealth of the environment, its unique wildlifeand the resilience of the entire lagoon system

■ Most scientific authorities are in agreementthat the most viable way to protect Venice from extreme flood events is to create a barrier

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Summary of conclusions continued

FUTURES

■ Human-induced climate change poses one of thebiggest long-term threats to the survival of Venice – sea level could rise locally by at least 8cm and as muchas 70cm by 2100

■ Predicting sea level rise is extremely complex andthere is much uncertainty regarding the scale ofimpact it will have, also depending on adaptation andmitigation measures

■ Radical ideas for saving the city include raising theground level by up to 30cm

■ The future health and survival of the city and lagoondepend on creating a balance between the needs ofthe environment, industry, agriculture, tourism andthe Venetians

■ Scientists need to work better among themselves aswell as to support greater stakeholder interaction ifsustainable policies are to be developed

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Setting“Venice is inconceivable without its lagoon;

it would not, could not, exist without its lagoon.” UNESCO RAMSAR Report, 2003

VENICE lies in the shallow waters of a coastal lagoon connect-ed to the northern tip of the Adriatic Sea. First occupied in thefifth century, it grew by the 14th century to be the magnificentcentre of a major maritime power. Today, it is a World HeritageSite, and the lagoon is recognised as a wetland of internationalimportance. From the beginning, Venetians have managedand modified their watery environment to suit their changingneeds, and the lagoon has adapted slowly. But the scale ofintervention in the 20th century, and its environmentalimpact, has been so great that both city and lagoon are now in serious decline. The relationship between man and theenvironment, city and lagoon, has changed from co-existenceto a type of conflict.

THIS CHAPTER EXPLORES■ THE SETTING OF VENICE IN A MARSHY LAGOON ■ THE PHYSICAL HABITATS OF THE LAGOON■ HISTORIC CHANGES TO THE LAGOON■ THEIR IMPACT ON ITS PHYSICAL AND BIOLOGICAL STRUCTURE

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left Seen from above: Venice, lagoon and sea are interdependent

Mediterranean. Tides rise and fall far more thanelsewhere in the Mediterranean, creating a uniqueecosystem that supports a rich biodiversity – someplant species exist only here; a few types of birdand fish depend on Venice for key stages in theirlifecycle and many species common in the lagoonare rare elsewhere in the Mediterranean. Manyimportant waterbirds, such as the redshank andthe Sandwich tern, breed here. And more birdsoverwinter here than anywhere else in Italy – thou-sands of dunlin, for example, stop off for thewinter to feed on the mudflats. The lagoon is actu-ally a fine mosaic of different habitats, each shapedby local conditions – the salinity of the water, orwhether it is calm and shallow or subject to fast-flowing currents.

UNDERSTANDING THE COMPLEXITYThis is ostensibly one of the most studied areas ofthe world – due to its compelling and longstand-ing integration of man and nature, its uniquebiodiversity, as well as the government resourcesand public institutions’ attentions to safeguardingVenice since the latter 20th century. However,there is still much to learn: advances in support-ing scientific theory, experimental techniques,physical, chemical and biological monitoring pro-grammes are improving our understanding of thephenomena. Meanwhile, the lagoon is changingfaster than ever before and human intervention ison an unprecedented scale. It is a difficult chal-lenge to achieve a solid knowledge base againstwhich to interpret the impacts, past and future, ofhuman activities. Much work has and is beingdone. Much more has yet to be done.

The changes in the lagoon are a result of a verycomplex mix of natural processes and humanintervention. To really grasp today’s challenges forVenice, we need to be able to understand the inter-action between the city, the physical processes that take place in the lagoon and Adriatic Sea, andthe chemical and biological ‘metabolism’ of the lagoon. Scientists observe and monitor thechanges in the lagoon in order to understand theprocesses occurring, but separating the cause fromthe effect in such a dynamic and complex system is problematic.

“The lagoon is one of themost studiedenvironmentsin theMediterranean,yet research is still neededto gain anintegrated and deeperunderstandingof itsdynamics”

Pierluigi Viaroli, Dept.of EnvironmentalSciences, Università di Parma

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Setting

VENICE lies at the northern tip of the Adriatic Sea,itself a northerly extension of the Mediterranean.The city is sited at the heart of a tidal lagoon, about50km long and 20km wide. A strip of land separateslagoon from sea, protected by sea walls and cut bythree inlets; several settlements are situated alonghere. Twice daily, tides flush the lagoon waters, andtheir ebb and flow shapes both lagoon and city.

17,000 years ago, during the last great ice age,the landscape was very different. The sea was 100metres lower than it is today and this region wasdry land. The seas rose as the ice age ended, and by4,000 years ago the coast looked much as it doestoday. Lagoon systems formed along the newcoastline as sediments carried down by the riversbuilt up banks and barriers, and marshes and mud-flats developed in the water trapped behind them.Venice lagoon and the Lagoon of Grado to thenorth are the only surviving examples; all the oth-ers have either silted up or been washed away bythe sea.

On such geological timescales lagoons are unsta-ble, constantly evolving systems. Their destiny is tomerge with either land or sea. Left to nature, Venice’slagoon would eventually have disappeared. The factthat Venice still exists is due to centuries of humanintervention – as we shall see later.

A PRECIOUS ECOSYSTEMVenice’s lagoon is a complex and delicate environ-ment, a place of ‘transition’ between terrestrial andaqueous environments, fresh and saltwater systems,and its physical form and biology are the result oftheir interactions. It is fed by freshwater and sedi-ments from the rivers and surrounding land, andalso by the ebb and flow of sea water through theinlets. Waves and currents shape its contours: so dothe plants that anchor the soft, muddy sediment,and the creatures that feed among them.

Overcome by the spectacular urban architec-ture, it is easy to overlook the fact that Venice’slagoon is a world-renowned wildlife habitat. It is thelargest wetland in Italy and one of the most impor-tant coastal ecosystems in the whole of the

City in the marshesVenice’s past, present and future depends on its relationship with water.To understand Venice, you must understand the lagoon

top Venice lagoon lies at the northern tip of the Adriatic Sea

above Venice city lies at theheart of the lagoon – thecanals are its ‘veins’ and‘arteries’, the saltmarshesits ‘lungs’. Large-scalecirculation through theinlets identifies threesectors: northern, centraland southern lagoon

above Saltmarsh showingSalicornia veneta, a specieswhich is unique to theVenice lagoon

far, right The lagoon is animportant sanctuary forwetland birds such asthese black-winged stilts

below, right Traditionalfishing in the lagoon usingan ancient technique. Inthe 19th century, 80 –90percent of fish were stillcaught this way. Use ofthis system is falling fastfrom over 100 fishermenfive years ago to less than 70 today

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VENICE’s lagoon is very shallow for most of its area: the average water depth is onlyabout one metre. Natural creeks andchannels wind across its bed, carrying tidalwaters between sandbanks, mudflats andsaltmarshes. Artificial navigation channels cutdeep into the lagoon bed, some as deep as 20 metres.There are four main physicalhabitats, defined in relation to the tides.Some 60 percent of the lagoon liespermanently under water; 25 percent isperiodically exposed to varying degrees by falling tides (marshlands and mudflats).The rest consists of islands, in principle always above water, although increasinglyvulnerable to flooding.

A Under water Open waters and shallowsincluding the natural creeks and dug channelsthat cut across the lagoon. The deepernavigation channels are marked out bydistinctive trios of wooden stakes. Seagrassesgrow in the shallows. They help to stabilise thelagoon-bed and are a nursery for fishreproduction

B Mudflats Low-lying areas exposed only at lowtide. They drain off the minor channels (tidalcreeks) and influence saltmarsh accretion anderosion processes. Although they may lookuninviting, they are rich in invertebrate life(including worms and clams – the latter areeconomically significant) and are important asfeeding grounds for birds

C Saltmarshes Higher-level areas, partiallycovered with water only at high tide. They are irregularly distributed around the lagoonand range in size from a few square metres to several hectares. Their salt-tolerant plantcommunities support a rich and diverse wildlife

D Islands These areas are not normally affectedby high tides: the islands (including Venice), isletsand the three strips of land separating thelagoon from the Adriatic (Pellestrina, Lido andCavallino), fronted by a sea wall

E Drainage basinF Fish farmG Sea wallH Adriatic Sea

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This illustration does not represent a real view, but bringstogether the main habitats and surroundings of the lagoon

Profile of the lagoon

INDUSTRY ARRIVESIn the 20th century, the pace of change accelerat-ed. Industry arrived at Marghera on the adjacentmainland and the port was moved nearby. Largeareas of marshland were drained for the industrialzones, airport and agriculture. The outer reachesof the lagoon were closed off to protect fish-farms,and new islands were created. Much deeper navi-gation channels were dug to bring far larger ships– giant oil tankers and container ships – into thenew port and industrial zone.

All these interventions have had major long-term consequences. The natural extent of thelagoon has shrunk by over 20 percent, and itsphysical structure and hydrodynamics (waterflow) has been changed for the worse: habitatssuch as saltmarshes have been lost and waterflows are now greater, which increases erosion. Inparticular, scientists have identified the deep navigation channels as major culprits in causingerosion and distorting the pattern of the tidal currents and trapping sediments, taking themaway from the inter-tidal areas.

VENICE was founded in the fifth century, afterpeasants fleeing from the barbarians found shel-ter on the small marshland islands of the lagoon.Over the following centuries, the city grew in sizeand importance. The original cluster of 118islands was built upon and gradually joinedtogether, linked by bridges, connected by canals.More marshland was drained. By the 14th centu-ry, Venice was the centre of a wealthy andpowerful European trading empire.

Venetians depended on their watery environ-ment for food, transport and protection – theshallow marshy waters of the lagoon werefamously ‘too shallow for invading ships, toodeep for marching armies’. The lagoon itself wascontinually refreshed by the tides, purifying andoxygenating the water. The lagoon waters flushedthe canal thoroughfares twice daily and carriedaway the sewage, which became nutrient for thelagoon’s plant and animal life. Venetians harvest-ed the shellfish and fish, and hunted thewildfowl. Many of the traditional techniques per-sist to this day and fishing still support the local economy.

“Too shallowfor invadingships, too deep formarchingarmies”

A history of interventionEver since people have lived in the lagoon, they have altered it to suit their needs.Now the scale of human activity threatens to destroy it

Paths of the lagoon’s mainrivers in the 14th century andthe less regular inlet system

By the 20th century, many ofthe rivers had been diverted,via canals, to north and south

CHANGING THE LAGOONUnderlying this intimate relationship between citi-zens and lagoon was a kind of compromise betweennatural forces and human needs. Natural processes,working over geological timescales, were gentlyshifting the lagoon to land, as the sedimentsbrought by the many large rivers that fed into itaccumulated. But the growing city depended oncanal navigation for the trade that brought it wealthand power, and for its protection. So a remarkablybold series of modifications began in the 15th and16th centuries to keep the lagoon under water.

Seven river mouths were diverted along canalsto north and south. Over the next couple of cen-turies, the diversions were adjusted further as theproblem of silting up shifted to new areas, or landbegan to erode.

The last great works of the Venetian Republic(which ended in 1797) were the conterminazionelagunare, which officially fixed the lagoon bound-aries, and built the murazzi, great sea walls designedto keep the Adriatic out. From the mid-19th to early-20th century, long jetties were built at each of theinlets to accentuate the tidal current which kept sedi-ments from clogging up new navigation channels.

above, left In the16thcentury, the main riverswere already beingdiverted fromdischarging into the central area of the lagoon

above The 20th centurysaw the growth ofindustry and otheractivites around thelagoon, including theairport (left of picture)

KEY CHANGES TO THE LAGOON

C13th–14th coastal protection – tree felling banned in coastal zone and chalk boulders positioned to strengthen sea defences

C15th–17th diversion of all large rivers discharging into the lagoonC18th construction of murazzi, sea wall defencesC19th–20th construction of jetties at the three inletsmid-C20th development of Marghera industrial area

reclamation of saltmarsh for agriculture landclosing off of fish farms construction of two major navigation channels

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MAPS, surveys and other historical evidence allshow that the lagoon is progressively evolvingtowards a marine landscape. The waters arebecoming deeper, marshes and mudflats are disap-pearing, erosion increasing, and the water hasbecome as salty as the sea.

It is difficult to quantify the change accurately,owing to the complexity of the processes and insome cases to a lack of data, but the problem arisesfrom a shift in the balance of sediments enteringand leaving the lagoon.

SEDIMENT LOSSSediment characteristics underpin many of thelagoon’s physical habitats and determine theirhealth status. Sediments range from fine mud andfluvial silts to coarser sand and their behaviourvaries accordingly. They are stirred up and redis-tributed by currents, deposited again elsewhere orswept out to sea on the tides. But while sedimentsare accumulating in some areas of the northernlagoon, in others they are eroding and overall, agreat deal of sediment is disappearing from thelagoon system. So the dynamics are extremely

complex. Measuring the lagoon’s ‘sediment budg-et’ – the material gains and losses over time – isessential to determining the fate of the lagoon inthe modern era. Yet it remains a hugely difficulttask. Although while most experts believe there isan annual net loss to the sea, estimates vary asmuch as ten-fold.

Sediment loss has been identified as a key fac-tor in the process of evolution from lagoon to bay. Diverting the rivers to prevent Venice fromsilting up has created the opposite problem –starving the lagoon of this sediment source. Thelong jetties designed to stop the inlets silting up with sediments have played their part in the sediment deficit. General deepening of the lagoon(explained in the next chapter) and deeper canals make currents stronger. Changes in current flows also mean that a great deal of silt and sandare drawn into the navigation channels from theadjacent shallows, which causes further erosionand has to be removed by costly dredging. Thetotal volume of water in the lagoon is said to have doubled in the past century, notwithstand-ing the reduction in total area, mentioned above.

Lagoon to sea Venice’s lagoon is becoming deeper and more like a sea bay. Its physical structure and ecology aredeteriorating, making the city increasingly vulnerable to storm surges and causing species loss in the lagoon

right Malamocco inlet Mathematical modelling reveals how the jetties at the inlets influence waterflows in and out of the lagoon, which in turn governthe sediment transport

A Early 1800sWater flows exit andreturn through the inletwith the ebb and flow of the tide, in apparentlyequal quantities

B NowJetties and associatedcoastal structures havealtered the flow ofwater, so that sedimentsswept out on the ebbtide are carried furtheralong by the coastalcurrent, which limits the amount of sedimentreturning to the lagoonon the subsequent flow tide

below, leftLagoon to bayThe bay is deepening,and the lagoon bed isbeing smoothed out.With deeper water anda loss of the dendriticstructure (creeks) andphysical habitats thatdampen down the effectof waves and currents,the tides and surges havea more direct impact onwater levels in the cityand lagoon

below Cross-section ofchanges to the lagoonbed due to erosion – an‘underwater desert’ insome areas

CLAM FISHING AND SEAGRASSES

CLAM fishing using large mechanical equipment (below) like this,causes long-term damage to the lagoon bed by stirring thesediments and interfering with the lifecycles of animals living inthem.The cloudy water prevents essential sunlight from reachingplants on the lagoon bed and the intensive harvesting of clams

dramatically reduces the population’s revival rate.The interference with seagrass communities is particularly significant, astheir long roots are neededto anchor the soft sediment(right). A major census of the seagrass communities,undertaken in 1990 and2002, has yielded a detailedmap of species distribution.A small general loss acrossthe lagoon over the previousten years is actuallycomposed of larger losses of species in some areascontrasted with theirreappearance in others.This study demonstrates the difficulty of makinggeneralisations about what is happening in the lagoon.

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Outgoing (ebb) tide incoming (flow) tide

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SCIENTIFIC surveys show that saltmarshes andmudflats are down to a third of their extent (about47km2) at the end of the 19th century. Around 20percent of the lagoon’s plant and 50 percent of itsbird species have been lost since 1930. Speciesthat live on the bottom of the lagoon were particu-larly affected, as much of the intricatesub-structure of winding creeks and meanderingcanals within the shallows have been destroyed bystronger currents and wave erosion. This lagoon‘physiology’ (habitats and structures) is vital toslowing the flow of currents in the lagoon, andtheir irregular form moderates wave energy. Theyare also critical to the chemical and biologicalfunctioning of the system.

Tidal creeks wind their way through a maze oftiny ‘islands’ of salt-tolerant vegetation on themarshes, specially adapted to the alternating wetand dry phases. As tidal creeks and natural chan-nels disappear, ‘ponds’ within the marshes areexpanding and joining up with the open water andfurther fragmenting the marsh structures.

Some areas of the lagoon are faring much betterthan others. The processes mentioned above have

removed nearly all saltmarshes from the centralareas. In the south, original reedbed marshes havetransformed into saltmarshes since the river diver-sions, but the process is all but stable. Only thenorthern lagoon retains some original characteris-tics and scientists are working hard to determineexactly what factors sustain them, so that moreeffective work can be done to revive and protectthe rest.

Looking to the future, many lagoon specialistsare concerned that with the lack of sufficient sedi-ments and rising water levels, the saltmarshes andmudflats will continue to degrade and possibly dis-appear within a century. Any sea level rise due tohuman-induced climate change will of courseexacerbate this trend.

POLLUTION HAZARDSIn addition to physical changes to the system, andthe effects on saltmarshes and their associatedecosystems, the lagoon was exposed to major pol-lution since the mid-20th century, with somedramatic consequences for the environment aswater quality deteriorated.

Venice’s lagoon is fed by a large drainage basin– a 1,850-km2 area – and despite the redivertion ofmany key rivers, there are still some river systemsand associated canals that flow into the lagoon.They bring with them toxic metals, pesticideresidues and nutrients from industry, agricultureand urban areas.

In the past, the lagoon trusted primarily intidal exchanges with the Adriatic and chemicalbreakdown by micro-organisms to cope with thisinflux. Micro-organisms in the mud and waterbroke down organic matter and waste water wasdiluted by the daily tides. But the input, since thelast century, of persistent and potentially toxicmetal and synthetic compounds, as well as greater quantities of other contaminants, hasmeant that the lagoon's natural waste treatmentsystem can no longer cope. Control of industrialwaste and agricultural run-off started in earnest in the 1990s, and a major integrated waste-watertreatment plant is currently being built. But thereis still an urgent need for the sewage inputs to the lagoon and canals of Venice to be more strate-gically addressed.

Ecological impacts Venice’s saltmarshes and mudflats are disappearing, starved of sediment and eroded by waves as the lagoon deepens

Main sources of pollution ● Agricultural run-off:

pesticides andfertilisers

● Industrial waste ● Urban waste:

sewage etc from Venice and mainland

● Air pollution:air and road links, industry

A Drainage basinB MestreC Port and MargheraD Venice

below, left Cruise ships enter through the Lido inlet, passthrough the Guidecca Canal and moor in Venice’spassenger terminal

below, right Industrial activity has leftareas of land adjacent to the lagoon that are highlycontaminated and large areas of Marghera now lie abandoned

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TOXIC TIME BOMB? Venice is one of Italy’s main ports, and majorchemical/petrochemical industries are still presentat Marghera. Both the port and the industrial com-plex were allowed to develop unchecked from the1950s, and used to discharge their waste directlyinto the lagoon. As well as the catastrophic risk ofoil-spills or chemical explosions in the lagoon, alonger-term threat exists.

Toxic metals (such as mercury, copper, arsenicand lead) and persistent substances such asorganochlorine pesticides and dioxins have accu-mulated in the lagoon sediment and canals,storing up problems for the future. Uncontrolleddumpsites in Marghera, created in the 1970s, arestill so toxic that they must be capped and isolatedfrom the lagoon system. Erosion and dredgingstirs up the sediment, sending pollutants backinto the system. Our understanding of the effectthese contaminants have on individual species isimproving, but their impact on whole ecosystemsis now a major area of scientific study. In addition,

as analytical methods improve and more contami-nants are measured, new threats to the system(e.g. endocrine disrupters) are emerging.

Preserving the lagoon’s unique ecology, whilestill maintaining the industry and port and otherproductive activities, has been, and will continueto be a major challenge.

EXPOSED TO THE TIDESLong-term studies confirm that the primary threatto the lagoon comes from its physical degradation –which strips away important habitats. Where therewas once a complex mosaic of habitats, there isincreasingly a scoured flat bay. The sedimentdeficit, the scouring of the navigation channels,and the decline of the biological communities, haveall led to the loss of key physical features and habi-tats, and deepening of the lagoon.

But deepening is also the result of global sealevel rise and the natural and human-inducedsinking of the land. In the 20th century, Venice lostsome 23cm in height relative to the water level. As the waters deepen and the tides’ impact grows, the problems of flooding increase. This isan immediate threat that must be confronted.

Ecological impacts continued

ALGAL BLOOMS Nitrogen and phosphorus compounds are vitalnutrients for a healthy ecosystem. But if there istoo much, the system suffers. A process calledeutrophication begins – the nutrients fuel explo-sions of growth in certain algae, robbing the waterof oxygen and starving out other species. In the1980s, Venice lagoon suffered terribly from densealgal blooms every spring, clouding the water andsuffocating life on the lagoon bed. Populations of alarger invasive seaweed called Ulva rigida alsoexploded, and soon accounted for some 80 per-cent of vegetation growth. It had to be harvestedregularly to stop it choking the lagoon.

Tough new regulations on industry and agri-culture finally brought the nutrient overloadunder control in the 1990s, but although phos-phates and ammonium levels have reduced, highquantities of nitrates still persist. It still isn’t fullyunderstood why the seaweed explosions diedaway, so logically it remains possible that they may return.

above Wave energy(moto ondoso), whichincreases as the watergets deeper in thelagoon, is a key factor inchanging the physical andecological structure ofthe lagoon. In more open parts of the lagoon,saltmarsh edges arecrumbling and vegetationis dying off. Higher waterlevels also mean that the marshes areunderwater for longer,which limits the viabilityof certain species

above, right Accumulation of ‘slime’ created by an algal bloom wherethere normally would be a pleasant lagoon beach at the island of Sant'Erasmo

CHAPTER 2 SUMMARY

■ Venice lagoon is a rich and semi-natural ecosystem, inextricablylinked to the life of the historic city and a unique ecosystemwithin the Mediterranean panorama

■ The lagoon emerged 4–6,000 years ago and 1,000 years ofhuman actions and interventions have had a profound effect on its physical structure and ecology

■ Today, the lagoon is at risk of becoming a marine bay, due toerosion of sediments and stronger water exchanges with theAdriatic Sea

■ As the water deepens, the city is more vulnerable to floodingand associated urban decay

■ Vital lagoon habitats have already been lost and those thatremain are under threat – and with them, the natural dynamicsthat the city depends on

In a healthy system, seagrasses grow on the lagoon bed, helping to anchor the sediment andmoderate wave action. Sunlight and oxygen penetrate the shallowwater and support their growththrough photosynthesis

When excess nutrients enter the system, algae reproduce rapidlycausing ‘blooms’ that consumeavailable oxygen dissolved in thewater. Tougher seaweeds like Ulva rigida thrive. Less vigorousseagrasses are smothered by these and, cut off from sunlight,they are unable to photosynthesise,and so die

As seagrass vegetation dies off,there is nothing left to anchor thesediment. It is swept up by currentsand clouds the water, furtherdecreasing sunlight penetration. Thelagoon bed becomes smooth and no longer dampens wave actions.Erosion therefore increases in afeedback loop, making it increasinglyhard for seagrass recolonisation

Effect of excess nutrients

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3

Flooding“No degree of flooding is acceptable

in a city of Venice’s supreme importance’’Anna Somers Cocks, Chairman, Venice in Peril

left Venetians are becoming used to regular flooding of their city

OF all Venice’s problems, flooding is the most obvious andimmediately alarming – water overflows the embankmentsand seeps up through the drains. There are two types ofacqua alta (literally ‘high water’): fairly routine inundation ofthe lowest areas of the city and rare but devastating extremeevents. While acqua alta has been a part of Venice’s historysince its foundation, flooding is on the increase, and it isdoing great damage to the city, both physically and socio-economically. More flooding is the result of a combination ofnatural forces (winter storms, combined with long-termprocesses of rising sea level and subsiding land) and man-made changes to the lagoon that have reduced its naturaldefences and caused the land to subside.

THIS CHAPTER EXPLORES■ WHY AND WHEN VENICE FLOODS■ WHY THE CITY IS FLOODING MORE FREQUENTLY■ HOW HIGH WATERS HARM THE CITY AND THE LIVES

OF ITS PEOPLE

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Why does Venice flood?

VENICE was built at sea level. Twice a day, thelevel of water in the city rises and falls as the tideebbs and flows through the inlets that connect thelagoon to the Adriatic Sea. The tidal range of over1m here is greater than at the southern end of theAdriatic, where tides usually vary by a few cen-timetres. But tides alone are not the reason thatVenice floods. The main influence comes from lowpressure weather systems and associated winds,which create storm surges that effectively pushmore water into the lagoon.

Two wind systems in particular create thesesurges. The Bora from the north-east acts locally todrive a high surge of water across the lagoon –sometimes creating a difference of up to 20cm inwater level between northern and southern partsof the lagoon. The south-easterly Sirocco wind,from the Sahara, forces surges up the long narrow‘funnel’ of the Adriatic Sea, towards the lagoon.Water rushes through the three inlets and sweepsacross it to the city – arriving at the Grand Canalabout 45 minutes later.

It was a very unusual combination of condi-tions – low pressure, persistent rain and highwinds – that caused the tragic flood of 1966,which took water levels in Venice nearly twometres higher than usual. Most people believe it isnow only a matter of time until the next disasterand there have been several incidents of grave (butnot catastrophic) flooding since then.

Flooding remains one of Venice’s most seriousissues not just because the 1966 disaster focusedattention on the vulnerability of the city’s preciousheritage and residents, but also because moderate(chronic) flooding is occurring increasingly fre-quently. This is because Venice has sunk. As it islower in relation to water level, lesser tidal surgescan cause flooding – and, as described in the previ-ous chapter, as the lagoon becomes more like amarine bay it has lost some physical features thatused to offer a natural dampening effect on incom-ing waters, so more water comes into the city witheach tide and surge.

Venice floods for many reasons: it is subject to storm surges, the land is sinking, global sea level is rising,and changes to the lagoon and its inlets have reduced its capacity to moderate water levels in the city

Main winds targeting Venice Responsible for stormsurges in the Adriatic:Bora – which blowsfrom the north-eastSirocco – which blowsright across theMediterranean from thesouth-east and up intothe ‘cul-de-sac’ Adriatic

MEASURING SEA LEVEL

LIVING so intimately with the sea,Venetians have always beencareful observers of water levels in the city. Sea levels in Venicehave always varied widely, not just over hours and months, butover longer timescales, which can make it difficult to deduce anemerging pattern or trend. Historical water levels have beenestimated using archaeological data from Roman times to the13th century – items excavated at differing levels are interpretedin terms of their assumed function, so a boat relic probablymarks water level whereas household objects would have beensituated a little higher than water levels in canals. From about the15th century, buildings were often engraved with a ‘C’ to showaverage high tide levels.This level is also marked naturally by agreen line of algal growth and some ingenious extrapolation hasbeen done by observing representations of the green line in18th-century paintings. Instrumental measurements began inVenice in the 1870s, and in 1897 a fixed reference point wasestablished at Punta della Salute, at the entry to the Grand Canal.Like the Venetians themselves, this reference point is used forexpressing water level throughout the book.

Average water level in Venice (commonly but inaccuratelyreferred to as average ‘sea level’) is calculated as a mean annualvalue, taken by averaging all the tidal maxima and minima for awhole year. But it is important to bear in mind that today’s meanwater level is about 25cm above the Punta Salute reference zero– the combined result of sea level rise and land subsidence. Thelowest parts of the city now lie less than half a metre abovetoday’s mean water level (70cm above the 1897 reference level)and are therefore vulnerable to tides only a little above average.

Flooding is largelyconfined to the winter months

Punta della Saluteis the referencetide gauge stationon the GrandCanal, in front ofthe old customshouse

Storm surge of 4 November, 1966During the main surge,waters rose more than1.9m above referencesea level, and beyond theinstrumental measuringlimit of the time. It wasfollowed by a series of‘seiches’, lower but stillhigh tidal surges that arecaused by the wateroscillating in the blindend of the northernAdriatic basin, and whichmean that severe stormscan have effects for days.

The dotted line showsthe ‘astronomical’ tiderhythm – the predictablerise and fall under theinfluence of the moon –and highlights theimportance of weatherfeatures in determiningwater level in Venice

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Normal tide range is between -50cm to +80cm, with respect tothe Punta Salute ‘zero’ reference. A ‘sustained’ tide is above80cm and an ‘exceptional’ event occurs when water level reaches110cm or above, and the Town Council’s flood warning system isactivated. (This is what is called ‘chronic’ flooding.) A level of atleast 140cm defines an ‘extreme event’. Sometimes severalflooding events occur over a number of days, as occurred in1966, due to seiches.

Forecasting sea levelThere is an extended network of tide gauges around Venice andthe lagoon which, in turn, are integrated with other sea levelmonitoring networks and meteorological stations across thewhole region. All this information is analysed (using mathematicalmodels and statistical analysis) to interpret past and presenttrends as well as to forecast water levels and flooding.

November 3rd 1966

astronomical tide

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Annual distribution of high tides >= +110cm (1923 to2003)

July Aug Sept Oct Nov Dec Jan Feb Mar April May June

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SINKING LANDIT was inevitable that Venice would sink. The landitself is subsiding naturally as the ancient sedi-ments of the coast settle. Also, the movement ofthe Earth’s crust (on a geological timescale), isdriving this part of Italy down under the Alps.Together these processes cause Venice to sink byabout 0.5mm each year, although the exactamount varies over time, from place to place – thenorthern and southern parts of the lagoon haveregistered rates of subsidence of a few mm/year.

That the city has not sunk more is thanks to alayer of highly stable, consolidated clay, known ascaranto, which lies several metres below the sur-face. This clay layer formed about 6,000–10,000years ago as the seas, which once covered thisregion, retreated. Venice’s foundations consist ofwooden stakes anchored in this layer and the natu-ral irregularity of the caranto is one of the reasonswhy ground levels vary around Venice.

Archaeological studies have calculated a loss inheight relative to sea level in the order of 1–1.5mma year. Architectural studies on the Basilica of StMark’s confirm this, revealing an estimated reduc-tion in the margin between ground level relative tosea level of about 14cm per century.

Sinking city, rising seasNatural processes are causing Venice to sink gradually, while the seas are rising around it.But human actions greatly accelerated the process in the 20th century

CITY ON STILTS

ASVenice moved fromtemporary refuge topermanent city in theninth century, peoplefound a radical solutionto building on theunstable marshy land.They drove woodenpiles – long, sharpenedpoles of alder, oak andlarch – into the morestable subsoil of clayunder the lagoon.Theairless muddy soilpreserves the wood and stabilisesfoundations (partlythanks to friction).

An astonishingnumber of pilings wereused: the Rialto Bridge isbuilt on 10,000, theChiesa della Salute onthe Grand Canal morethan a million.

A layer of oak waslaid across the piles toform a foundation.Above this was placed a layer of Istrian stone,a tough marble from the mainland that isimpermeable to water.This provided aprotective barrieragainst the lagoonwaters.

Above the water line,lighter-weight materials– brick, wood andplaster – were used.Thisreduces the compactioneffects of the buildingsand confers flexibility asthe various groundlayers shift continually.

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above Sea level rise in Veniceand Trieste, separated by100km in the northernAdriatic.The rate of sea levelrise was the same in bothplaces until the strikingacceleration in Venice, from

the mid-1920s.Today, therates are back in line witheach other (dotted line),although relative sea level inVenice is now higher due tothe subsidence caused bygroundwater extraction

Rising average sea level inVenice: the general upwardtrend is clear althoughvariations from year to year are significant

GROUNDWATER EXTRACTIONThe rate of land subsidence in the lagoon acceler-ated dangerously in the last century. From the1920s, industries started to settle on the mainlandperimeter in the area known as Marghera, and theport of Venice was also relocated here. The hugevolumes of water needed to support these activi-ties were pumped out of deep aquifers (naturalunderground reservoirs) beneath the lagoon.Unfortunately, it was not realised for decades thatthese aquifers were an important ‘cushion’, buoy-ing up the land on which Venice rested. Landbegan to subside dramatically, as can be seen froma comparison with measurements at Trieste, whichis subject to the same ‘background’ subsidenceand sea level rise.

In less than 50 years, from the 1920s to 1970,Venice had sunk by approximately 10cm more thanTrieste. Alerted by geotechnical specialists, whoattributed this dramatic drop to groundwater pump-ing in 1970, the government banned it and thesubsidence rate adjusted back to normal within a fewyears as the aquifers refilled. However, the damagehad largely been done in terms of Venice’s protectivemargin against flooding and the land rebound wasrelatively small (2cm) as the basal clay on which thecity rests had been irreversibly compacted.

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Sea level measures with reference to Punta della Salute

this in more detail). Although it is the extreme events that Venice

fears most, it must also cope with and plan for ageneral and gradual rise in water levels. Since the1966 flood, people have moved from vulnerableground-floor homes, but stores and workshopsremain at risk. The city’s highest land is no morethan 2m above sea level, and much of the city liesmuch lower than that. Areas that were once safe,now flood, and low-lying areas are flooding withincreasing frequency.

RISING SEASSubsidence of the city has been accompanied by agradual worldwide sea level rise. In line with ris-ing global average temperature, seawater volumeexpands and land-based ice melts, raising sea lev-els across the world. This global process is knownas ‘eustasy’. Concerns for Venice’s future are inpart based on predictions of a global rise of about8–88cm by the year 2100, but the regional impli-cations have yet to be worked out. At least for thetime being, sea level rise in the Adriatic regionseems to have slowed down (Chapter 6 explores

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Sinking city, rising seas continued

These two maps show that much more of the city floods todaywhen water levels risethan a century ago

CLUES FROM CANALETTO

CANALETTO’s meticulous paintings of Venice in the 18thcentury provide a unique historic record of the city’srelationship to the water, because of their accuracy. Canalettoand his student and nephew Bellotto used a ‘camera obscura’to paint their scenes.This device reflects a mirror image of theview onto paper, which can then be traced on – the picture isin essence a photograph. Modern photographs from the same

viewpoint have been used to compare water levels – and revealwhere ground levels have changed.

The Punta della Dogana example shown here illustrates thedifference clearly.The bases of the columns to the right show that the whole pavement has been raised, and still the wateris higher up.The rise was calculated as 70–110mm overtwo centuries.

2000

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FLOODING IN VENICE TODAY

Water level Area of city flooded (cm) (%)

25 0 (today’s mean sea level)

70 St Mark’s Square and Basilica begins to flood

100 3.5

110 12

120 35

130 69

140 90

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Today

Turn of the 20th century

“Venice has lost a century in its battle with the sea” Prof Albert Ammerman,archaeologist, ColgateUniversity, USA

Areas flooded in 1900, when water level at:■ 120cm■ 140cm(no areas flooded at 100cms)

Areas flooded 1997, when water level at:■ 100cm■ 120cm■ 140cm

Flooding since 13thcentury, partly based oninterpretation ofhistorical accounts of thelife and times of Venice

Since 1923 there hasbeen an increasingfrequency of ‘normal’flooding events (over80cm) – when less than3 percent of the city is inundated

Analysis of the past 30 years’ data showsfewer than four such‘extreme’ episodes per year

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THE first record of acqua alta dates back to 1240,when waters were ‘above man height’ in thestreets. It is something people have learned to livewith but, increasingly, the dampness and compli-cations caused in daily life are becomingunbearable. Today, in winter, raised walkways(passarelle) are out most of the time in the low-lying areas and along strategic routes, such asfrom the railway station. Water wells up fromdrains to pool in the city’s squares and court-yards, and may flow over the canal banks. Manyentrances to buildings, schools, shops, store-rooms and church crypts flood, while mostground-floor dwellings have been abandoned.Even emergency services are jeopardised by highwaters when water level in the canals leaves toolittle space under bridges for the fireboats andambulances.

The present situation is significantly worsecompared with 100 years ago. Of the ten highesttides (above 140cm) recorded in the century to2002, eight occurred after 1960. In the winter of2002 alone, in the space of three weeks (14November–8 December) there were ten floodevents above 110cm, five above 120cm and oneabove 140cm. But the picture is complex due toirregularity within the general trend. In the wholeof 2003, water level did not rise above 110cm.Only by comparing data over many years canmeteorologists be sure that the frequency offlooding is not just linked to some cyclical trendbut a permanent change.

Scientists have linked increased flooding tothe rise in average sea level attributable mainly tothe episode of human induced subsidence, and tochanges in the lagoon’s physical structure, whichaffects the entry and movement of water within it.Changes in the shape of the inlets, loss of salt-marshes and deep navigation channels havecontributed to a greater volume of water andstronger current entering the lagoon whenpushed by the tide and winds. A small effect isalso attributed to the reduction in total area of thelagoon, due to land reclamation and other inter-

ventions, so the greater volume of incoming waterhas less area in which to spread itself.

Even when the tide is not particularly strong,high water regularly tops the protective layer ofIstrian stone on the canalside buildings to eataway at the plaster and brickwork physically(wave and propeller energy) and chemically (saltscorrosion). The city is under siege.

Flooding more frequentlyFlooding in Venice is occurring more often. In winter, what was once an occasional event is now analmost daily occurrence in some parts of the city

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Annual distribution of high tides>= +80cm recorded by the Punta Salute tide guage (1923–2003)

Annual distribution: high tides >= +110cm recorded by the Punta Salute tide guage (1923–2003)

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“Venetians havebeen gettingtheir feet wet for centuries”

Paolo Costa, Mayor of Venice

VENICE’s architectural problems are not new. Thebattle to maintain the delicate fabric of the city hasbeen relentless. Up until the 19th century, canalswere filled in, buildings demolished and rebuilt inthe face of changing water levels, but Venice’s‘forma urbis’ and architectural heritage is nowunder strong preservation orders. Today, the city’sextreme fragility is startlingly obvious – especiallythe many crumbling buildings that have beenabandoned as a result of the collapse in the localpopulation and the relocation of many offices andbusinesses to the mainland.

The main decay is caused by the destructiveaction of sea water. Since the tidal exchangebetween the lagoon and Adriatic has becomestronger, salinity of the canal water is the same asthe sea. On many buildings, water level nowcomes above the impermeable Istrian stone basefor most of the time, soaking into the porous brick-work, wood and plaster. Dissolved salts degradethe building fabric as they crystallise within thewalls. Air pollution used to be a problem and cor-roded the marble facades of Venice’s palaces. ButVenice was one of the first Italian cities to convert

City under attackVenice’s world-famous architectural heritage demands constant attention. High waters, wavesgenerated by boats and pollution all attack its fabric and foundations

BASILICA

FOUNDED in 829 AD, in honour of the city’s patron saint, St Mark’s Basilicais the city’s most famous building, and one of its most vulnerable. Its cryptnow lies some 20cm below sea level, nearly 170cm lower than when it wasbuilt.Water invades the atrium between 150 and 180 days a year (nearlyevery day in winter), when the tide touches 67cm above reference zero.Aswater level rises, it starts to seep up through the foundations, while outsidein St Mark’s Square, it comes up out of the storm drains to flood thepavements. In winter, the vestibule is commonly ankle-deep in water. Thefloor of the Basilica has been raised many times in the past, and the squarehas been repaved. But today this is no longer an option: further raising woulddestroy the architectural quality of this magnificent church. Other remediesmust be found (Chapter 4 explores works underway in greater detail).

left Fast and intense boattraffic causes damage –by setting up higherwaves, and ‘sucking’ atthe foundations. Studiesare still trying to assessthe consequences ofpassing cruise ships forbuildings and air qualityalong their routethrough Venice

above Cross-sectionthrough building showingstructural damage.Motor boat enginepropellers causescouring of the mortarsand brickwork belowwater. Wave energy andthe infiltration ofcorrosive salts andsediments clog sewageoutlets and drainpipes,which then burst withinthe building walls.

CHAPTER 3 SUMMARY

■ Flooding is caused primarily by stormsurges – winds that drive water into the lagoon

■ Many man-made changes haveinadvertently reduced the lagoon’sresistance to incoming waters, against a background of sea level rise – hencehigher tides

■ It is not a new phenomenon for Venice,but the damaging effects of floodingcreate an insatiable demand for urbanmaintenance and are gradually drivingthe population away

■ The idea that Venice is sinking comesfrom the extraction of groundwater inthe mid-20th century, which causedmajor land subsidence.This has now beenstopped and Venice has returned tosubsiding naturally and gradually

■ Barriers at the inlets will protect Venicefrom extreme water levels; othermeasures are being taken to protect the city from medium-high tides and‘chronic’ flooding

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to methane power generation (instead of coal andoil) and industrial emissions are being controlled.

TRAFFIC WAVESBuildings are also challenged by waves set up byspeeding boats carrying people and goods throughthe city’s canals. The intensity of the waves hasbeen estimated as adding a few centimetres to themean water level. While the waves attack surfacesabove water, the action of propellers below watercreates a sucking force, eroding cement and foun-dations. Stirred up sediment clogs the canals andobstructs the ancient sewage system on whichVenice still relies.

The impact on the people of Venice is enor-mous: the inconvenience of flooding, and theongoing damage to their fragile buildings, and theoverwhelming presence of tourists have meantthat many Venetians have abandoned the histori-cal centre as a place to live or work. In the 1950sthe city boasted a population of 150,000. Today, itis closer to 65,000. If future generations are to bedrawn back to the city, remedies are urgently need-ed to mitigate flooding and urban degradation.

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Remedies“Our goals are to restore and re-equilibrate

the lagoon, and eliminate the causes of environmental degradation”

Maria Giovanna Piva, President, Venice Water Authority

left Building maintenance is a constant necessity from the foundations upwards

THE complex problems of Venice and its lagoon must beunderstood as a whole, since the health of one depends criti-cally on the health of the other. An integrated programme ofdefences has been outlined to protect Venice from the acquealte, and to reverse the degradation of the lagoon environment.The urgent and constant need for interventions to restore andpreserve the fabric of both city and lagoon, and to protect themfrom floodwaters, go hand in hand. There are enormous tech-nical challenges, which involve establishing priorities, recog-nising the different timescales for action and managinguncertainty. Much of the work involves tested engineeringapproaches but some of it is experimental in nature.

THIS CHAPTER EXPLAINS■ ‘LOCAL’ MEASURES TO PROTECT VENICE AND THE OTHER ISLANDS ■ THE RESTORATION OF VENICE’S BUILDINGS AND INFRASTRUCTURE ■ BUILDING NEW SALTMARSHES; THE RESTORATION AND

CONSERVATION OF REMAINING ONES ■ OTHER ‘DIFFUSE’ MEASURES IN THE LAGOON ■ THE NEED FOR FLOOD CONTROL OVER AND ABOVE THESE MEASURES

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argue that tackling environmental degradation ofthe lagoon can be dealt with separately over alonger timescale. Others, who oppose the barriers,would prefer to see the local and diffuse measuresprioritised to combat the chronic flooding prob-lem and deal with the environmental degradation.

LOCAL DEFENCESLocal defences are designed to protect the built-upareas from flooding. The first of these measuresinvolves raising pavements, bridges, embank-ments and walkways as well as subsidising anti-

flooding measures for the ground floor of manybuildings, especially in the lowest-lying areas ofthe city and other islands. The stated aim is todefend the city against medium-high floodingtides (up to 110cm above the reference level) and,where possible as high as 120cm.

Historically, Venetians have responded to ris-ing water levels by knocking down old buildingsand building new ones, or by simply filling incanals, and raising the floors and pavements.There has been much discussion about whetherit is possible just to continue this habit to keeppace with the waters. But, in the opinion of manyexperts, the limit has been reached if the architec-tural glories of Venice are to be preserved, as rais-ing pavements any further will destroy theelegant proportions of the buildings and elimi-nate features such as the bases of columns. Doing

so would create a different Venice, and it is not anoption that most people are prepared to acceptfor this World Heritage Site. With local defencesonly of the order of 110cm, the barriers will bevital in defending Venice’s iconic buildings andresidents from extreme floods.

Another category of local defence works isknown as insulae (islets), which go beyond sim-ply building up ground levels and include theimpermeabilisation of an entire islet area withinthe city, via complex interventions on thedrainage system, use of one-way valves and spe-cial materials to block the seepage of under-ground waters.

More ambitious schemes to raise wholebuildings or entire areas of land using innovativetechnologies are still technically uncertain, butthey remain a long-term option (See Chapter 6).

AN integrated system of defences has been out-lined to protect Venice from the acqua alte. Theseare classified into:■ ‘local’ (city and other inhabited islands)■ ‘diffuse’ (lagoon-wide)■ ‘coastal’ and large-scale engineering (the barrier

scheme and shoreline reinforcement). The Comitatone determines safeguarding poli-

cy, while the Consorzio Venezia Nuova is chargedby the Venice Water Authority with planning,designing and implementing them – as far as thelagoon is concerned. Insula SpA does the same forthe urban areas of Venice and the islands. Bothwork with regional and local authorities and otherkey bodies.

The proposed scope of works is vast: embank-ments and walls are being raised against the risingwaters; canals require dredging; kilometres ofbuildings and canal embankments need to berestored from the foundations up; the entiresewage system and underground drains need to berepaired and modernised. Out in the lagoon, thesteep decline in physical and ecological status hasto be redressed, in order to restore the naturalresilience of the system, and new flood protectionmeasures must be put in place. At the coast, thesea walls need strengthening, while flood barriersand associated works are to be built. It is anextraordinary, ambitious programme, calling formore integrated analysis of the past 30 years’acquired scientific knowledge, sharing of data andcareful monitoring of the effects and impacts ofinterventions – during and after implementation.

DEBATING THE PRIORITIESThere is considerable debate in Venice aboutwhich of these safeguarding measures should takepriority, and indeed whether they are all necessaryto protect the city. Some scientists and engineersfeel that the mobile barriers (discussed in Chapter5) need to be built immediately to eliminate therisk of another devastating flood like 1966. They

Defending the cityProtecting Venice from flooding requires a high degree of planning and coordination. The currentprogramme of works is also a great opportunity to renew the city’s infrastructure

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ARCHITECTURAL SURVEYS

IN 1999, the Comitatone requested clarification on the realpotential to raise ground levels throughout Venice,“tendingtowards 120cm”. Studies were commissioned by the Comune(Insula and COSES) and by MAV-CVN (IUAV-ISP, a consultancygroup within Venice’s Architecture University). Each study groupadopted a different approach and set of parameters, and theirconclusions were different. IUAV did an intricately detailed surveyof three areas of the city and highlighted the difficulties ofgeneralised ground raising against a background of highly variableand intricate architectonic and aesthetic building features.

Insula, on the other hand, concluded that it would be realisticto aim for local defences of +120cm relative to water level,although the details of each intervention must be evaluated on acase by case basis. Insula also applies a less restrictiveconsideration of architectural features which allows, for example,steps to be covered by higher paving and architraves to beknocked out to allow the height of a doorway to be increased tocompensate for a higher threshold. Both analyses represent anextraordinary record of the city today, and a powerful resourcefor the future.

To date, Insula has completed more than 15 percent of the100,000m2 earmarked for raising and it has also taken a further15,000m2 of walkways which were already at +110cm to +120cmor above. On average it has added 8cm to relative height, which

corresponds to a 50 percent reduction in flooding frequency.A further 30,000m2 of embankments, including the islet of St Mark’s has been assigned to MAV-CVN.

left Archaeologists haveuncovered evidencethroughout the city ofrepeated raising of floorlevels to beat the risingwaters. Here a column’sbase is now manycentimetres below thecurrent floor level

above Ad-hoc measures to keep out thefloodwaters can be seen everywhere in Venice

above Analyses of the proportions of doorways, and how they might be modified if pavements were raised. Insula considered 13,000 units with less restrictive parameters and IUAV surveyed 9,300 units with great attention toretaining distinctive architectural and historic features

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CURING SALT DAMAGE

SALTWATER and sea air attack both above andbelow the water line. In the past, Venetianbuilders created a damp-course at the base oftheir buildings, using non-porous Istrian stone.The underwater depth of the stone facing wasdetermined by the then high tides, with a built-in safety margin. Now that margin has been lost.Saltwater penetrates and rises in the brickwork.Once the water evaporates, the salt left in thewall crystallises, expanding and so increasingpressure on the bricks, which crumble alongwith plasterwork. Extensive research hasresulted in the development of innovativechemical and physical treatments to protect thebrickwork and block salt invasion. Some vergeon pure alchemy, others are simpler – forexample the use of outer plasterwork as a‘sacrificial layer’ in which the salts concentrateand crystallise, rather than staying within the brickwork.

MAINTAINING Venice has been a constant chal-lenge ever since the city was built –- water and seaair are naturally corrosive, while modern pollutionalso attacks marble and plaster. Venetians haveworked hard to preserve their city – althoughurban maintenance took a back seat in the post-World War Two period, efforts were intensifiedfollowing the shock of 1966. Despite the past 30years’ work, there is still much to be done torestore and maintain the city’s urban fabric.

In the 1990s, Venice Town Council linked upwith key service industries – water, gas, electrici-ty and telecommunications – to form a companycalled Insula, to develop and run a massive inte-grated project to protect and restore the city.Raising ground levels for local flood protectionwas synergised with renewing the city’s ageingroot-and-branch infrastructure, and dredgingthe canals.

Periodic dredging operations have been per-formed since ancient times to permit navigationand to maintain acceptable hygienic conditions.From the early 1960s to late 1990s, however, thedredging was interrupted, except for some minorinterventions, and a layer of sediment up to 1mthick accumulated in the network. Canal dredg-ing to improve water circulation and navigabilityis now combined with repairing building foun-dations, increasing the number of septic tanksand the renewal of the culvert system. Disrup-tion to the city’s life is enormous – pipelines arebeing laid, bridges and walkways are beingrebuilt, canals are drained while workmenreplace and consolidate the brickwork and injectit with innovative chemicals.

Once canals are dredged, the foundations areaccessible and repair work is more easily done.An extensive programme of work on dredgingand repairing the canals is underway, and urgent-ly needed modernisation of the sewage network,to include a collection and treatment system for

the historical centre, is being discussed. Venicehas no sewage treatment: traditionally the citydischarges its waste untreated into the lagoon,relying on the tides to flush the canals clean. Buttoday many wastewater outlets, constructed cen-turies ago, are covered by mud in undredgedcanals or clogged by fine sediments, stirred upby boat traffic and the tides. This weakens build-ings as the old pipes disintegrate and releasetheir contents within the walls. Fluctuations inwater pressure can also damage foundations andcanal banks. On the mainland around thelagoon, new treatment plants and modern sew-ers are already being put in place to stop theinflux of nutrient-loaded sewage into the lagoon.

Repairing and renewing the cityWork to rescue Venice’s crumbling fabric was given new impetus with the Special Laws, which led to the development of a large-scale programme of restoration, renewal and flood protection

above Replacingcrumbling brickwork

right Laying newelectricity and otherservice networks acrossthe city

left Repairing a sewage outlet

below The canals are dredged to get at the foundations and underwater sewage drains

Salt-damaged brickwork

Workmen injecting brickwork withconsolidating and stablising materials

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Damagedpaving, brickand stone

Restored pavingand brickwork andnew masonry, newrainwater sewer and erosionprotection

Quayside

Piazza

Damagedpaving andbroken,collapsingconduits

Restored paving andconduit, augmented by a new rainwaterdrainage system

Rescuing St Mark’s SquareST MARK’s Square, Venice’siconic landmark and symbolof its past glory, is the targetof a special programme offlood protection and repair.It is an example of theinsulae approach toimproving defences againstmedium-high tides. Work isproceeding in small sections,so that the Square remainsaccessible to the thousandsof daily visitors.

Phase One, started in2003, consists of repairingand raising 150m of quaysidewalls to +110cm to stopwaves and floodwaters fromflowing over the banks.The pavement within theSquare cannot be raised anyfurther, or the architecturalproportions of its uniquebuildings will be ruined.

Phase Two consists ofreorganising and modernisingthe existing network of pipesand drains underneath theSquare, and fitting one-wayvalves to stop the backflowof water up to the surface.Underground conduits willbe completely restoredwhere they have collapsed.A waterproof layer may beadded to prevent seepagethrough the subsoil, but thisis subject to further research.A new rainwater collectionsystem linked to a pumpingstation will actively pumpwater back out to thelagoon at high tides.

EROSION, high waters and wave motion aregradually transforming the lagoon into a marinebay. It is losing its physical characteristics andhabitats. The ‘diffuse’ measures proposed acrossthe lagoon seek to reduce the height and impactof high tides and, in addition, to restore thelagoon morphology. This second line of defenceaims to restore the natural defences that havemade possible Venice’s long history, workingwith nature rather than against it. The lagoon’sphysical and biological structures used to helpdampen the effect of acqua alta but over the lastcentury so much has been damaged and erodedthat the seas flow more freely into the lagoon andeasily penetrate the canals of Venice. The meas-ures will have an impact on the water levels butcannot solve the flooding problem, although theymay reduce the frequency of flooding. They will,however, play an important role in reversing thedegradation of the lagoon.

The ‘diffuse’ measures include works on salt-marshes, further investigation and pilot studies toquantify the potential of opening areas to tidalexchange, filling-in dredged navigation canals andmodifying inlets. Additional measures aimed atprotecting the lagoon rather than influencingflooding include improving the ecological qualityin some areas; controlling the release of pollutionfrom sediments and especially from the dumpsites where industrial wastes were previously dis-posed; planting seagrass to help consolidatemuds; improving water quality; protecting andreintroducing saltmarshes. There is no one solu-tion to protecting Venice and its lagoon as a com-bination of approaches is needed. Also, theseproposed measures are not all feasible, but doform part of the debate of which remedies shouldbe undertaken as a priority and over whattimescale.

Protecting the lagoonA second layer of ‘diffuse’ measures covers flood defences and environmental restoration across thelagoon. They help to protect Venice, mitigate the tides and revive the lagoon’s degrading habitats

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below The northernlagoon seen from thebell tower on the island of Torcello – this areabest conserves theoriginal characteristics of Venice lagoon

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Revitalising the saltmarshesIn the debate on the future of Venice lagoon there seems to be a common aim: guaranteeing theconservation of this unique system. Experimental restoration work is taking place in 20 locations

AS described in Chapter 2, the lagoon’s salt-marshes and mudflats are still disappearing at analarming rate as a result of reclamation, erosion,pollution, and natural and human-induced sub-sidence. Reconstructing lost saltmarshes andprotecting and restoring the existing ones is amajor technical challenge. Their natural formsare the result of evolving conditions, an intricatebalance of interacting processes – the energy ofthe waves and the ability of the structures todampen them, the amount and flow of sedimentin the system, the biological mix of species. Anyattempts to reconstruct or restore these habitatsmust be based on an understanding of how thenatural system works. It requires innovativethinking – and many of the techniques beingtried out are highly experimental. It is, anyway,impossible to return to the lagoon as it once was:it is deeper and more open to waves than before,and the dynamics of flow are now quite different.

RESTORING OLD MARSHESTo restore the existing marshes to health, it isvital to protect their eroding edges and give themtime to build up again. A range of experimentaltechniques are being trialled, using woodenpiles, gabions (wire cages containing rock orother material), artificial sandbars and beaches.Other experiments include measures to encour-age sedimentation and new growth: sedimentfences, spraying the marsh with nutrients anddepositing new organic matter at the edges, andtransplanting vegetation. Water quality can beimproved by re-opening tidal creeks. Pollutedmudflats are being capped to prevent their sedi-ments being stirred up into the water column.

CREATING NEW MARSHESIn some areas new marshland is being createdusing dredged material, taken from navigationchannels in the lagoon and near the inlets. By theend of 2000, 15 percent of total ‘marshes’ in the

lagoon was now of this type. These are highly managed systems, with solid edges to prevent theunstable sediment from being washed away againby the waves. There is already concern that theirsteep edges mean they are not linked with mudflatsthat grade into natural saltmarshes. They are dis-tinctly different in character from the other marshareas, their structure a ‘cruder’ version, with lessphysical and biological complexity. The questionis whether they develop into stable, complex com-munities over time which are comparable to theVenetian saltmarshes.

These are long-term experiments, and theresults will not be apparent for decades. They

require continual monitoring and testing by scien-tists to follow their progress. Lessons have alreadybeen learnt. For example, there is now a moveaway from using hard structures to using degrad-able materials and engineering solutions that arecloser to the natural structures and processes.

The illustration over the page shows some of the key restoration projects. As a summary diagram, itdoes not reflect any one place – these measures arebeing tried out in many different locations.

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HYPOTHETICAL MEASURES

Re-opening areas of the lagoon

IN the last century, the area of lagoon open tothe tides shrank by about 20 percent.The fishfarms, situated at the lagoon periphery to thenorth and south, are now separated from thelagoon by embankments, isolated from the ebband flow of the tide. Other areas of the lagoonwere made into artificial islands, mainly in the1960s, in anticipation of an industrial expansionthat never happened. These are to be openedup by digging tidal creeks through them, andplanting them with vegetation to encouragethe return of saltmarshes, as part of the Fusinawater treatment system.

Opening these areas would allow the tidalwaters to be dissipated over a larger area. Butstudies have shown that it would only slightlyreduce water levels.Also, the farms areprotected by powerful interest groups,including recreational hunting.

Navigation channels

THERE has also been much debate aboutfilling in the major navigation channels (notablythe Canale dei Petroli that links the Adriatic toMarghera, via the Malamocco inlet) which arewidely considered to be a major cause oferosion processes in the central lagoon.At the moment, inter-tidal sediments areresuspended by the influence of the currentsin the deep channels, which is where they re-deposit, only to be lost from the system as they are carried out to sea by the strong currents.

Filling in the channels would reduce theamount of sediment lost from the inter-tidalareas and impede the dissipation of waterentering the lagoon at high tide. But thesechannels carry important traffic to and fromthe Port ofMarghera,and there isequal pressureto keep themopen anddredged –studies haveshown thatfilling-in theCanali dei Petroliwould havelittle influenceon the waterlevel andflooding of Venice.

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above Natural saltmarsh

far, left Fishermen set out their nets in theopen lagoon and themarshes. Fish such asgrey mullet and flounderare caught when theybecome trapped by thechanging tides

Container ship off-loading

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Experiments in restoring saltmarsh

Protecting the edgesThe areas where restoration is being trialled are afflicted byeroding edges, where the deepening lagoon and greaterexpanse of open waters produce higher and more powerfulwaves, which batter the marsh banks. Invasive seaweeds havealso killed off vegetation that helped protect the margins viatheir root systems. Eroding shallows are another problem,as the disappearing mudflats used to dampen the force ofthe waves and supply sediments and ecological relationshipsto nourish the marshes.

A Hard ‘gabions’ (wired crates of stones) have been tried in more exposed areas, but can cause local wave actionand thus increase local erosion.They also interrupt the natural process of exchange between the marshand adjacent mudflats.

B Biodegradable gabions (sacks of sediment and/or bark)planted with pioneer vegetation are designed to dampenwave forces while they degrade gradually, allowing naturalprotective saltmarsh regrowth to take their place.

C Simple woven brushwood fences help to protect edgesand increase sediment trapping by 1–3cm a year. Theyrequire constant maintenance.

D Wooden pilings are considered an alternative to hardgabions.

Restoring the vegetationE By replanting helps to stabilise the lagoon bed –

by trapping sediment in the shallows and triggering theprocess of rebuilding the marsh.

Feeding the marshesF Boats can be used to replenish marshes with a fine spray

of sediment.

Dredging the tidal creeksG Excavating is done to improve flow through the marshes,

to facilitate water and nutrient exchange.

THIS summary illustration shows a range ofrestoration techniques being tried out around thelagoon. Applications need to be monitored fortheir effectiveness in developing stable, healthysaltmarsh communities in order to guide futureprojects.Techniques are being shared around theworld, especially with the North Sea (Germany,Holland and UK) and Chesapeake Bay (USA).

events, like the storm of 1966. Nor can they offerprotection from inevitable long-term global sealevel rise. Studies aided by computer simulationssuggest that neither the lagoon-wide restorationefforts nor the changes to the lagoon inlets(presently under construction) will be able toreduce high water levels in Venice by more than afew centimetres.

Measures in the city and across the lagoonwould have to be far more drastic, and unaccept-able in view of the world importance of its archi-tectural heritage. And most people are certain thatit is only a matter of time before another major dis-aster happens.

The consensus is that the only feasible way tostop the rising waters from overwhelming the cityagain is to provide a physical separation from the sea.

THE coast is the lagoon’s first natural defenceagainst the sea –- waves lose their energy as theybreak on beaches that form a barrier across thelagoon. But erosion has progressively reduced thebeaches to the point where some have disap-peared altogether, as has the dune belt behindthem. These natural structures reduce wind actionand trap windblown sand, and are also importantwildlife landscapes. There are numerous smalltowns and villages along the Venice coast, makingprotection here even more vital.

Coastal defences include creating new beachesand widening existing ones. The ancient sea wallsand jetties require maintenance, and new groynesare being built out from the beaches to dampenthe effect of storm waves. Sand dunes also need tobe conserved and preserved, with the added bene-fit of bringing wildlife back to the bay.

TIDAL INLETSThere has been much debate about how to alter thethree tidal inlets, at Chioggia, Malamocco and theLido, to restrict the amount of water entering thelagoon. Some scientists have supported proposalsto narrow the inlets and where possible to reducethe depth and roughen the seabed there. Thiswould create higher resistance against water flowinginto the lagoon during a strong surge, resulting in alower volume of incoming water over a given periodof time and a lower peak water level. The effect ofinlet modifications would be less for normal tidesand almost negligible in a 1966 type event.

Other scientists argue whether this approach is useful as part of the overall safeguarding meas-ures due to long-term impacts on the water flowsand sediment processes. The Comitatone agreedin 2003 that some changes to the inlets will occuras part of the so-called ‘complementary meas-ures’ discussed in the next chapter.

A HUGE CHALLENGEThe task is a vastly challenging one, as each change

made to the lagoon will ripple through the system.Many measures are experimental and what works‘on paper’ may not work in practice in such a com-plex, multi-dimensional system. Detailed researchand constant monitoring is needed to track thechanges and measure their impact.

At the same time, scientists are still working toestablish a sufficiently detailed baseline of informa-tion about the lagoon’s behaviour today. Withoutthis, they cannot accurately judge the true impactof the changes.

IS IT ENOUGH?Could the local and diffuse measures described inthis chapter be sufficient to protect Venice fromthe floods?

While a few people argue that they will, themajority of scientific opinion is that, although theyhelp limit the number of floods they are not suffi-cient – they cannot protect the lagoon from extreme

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Measures at the coastThe proposed programme of protective measures continues at the coast, to restore existing defencesand alter the inlets to increase their dampening effect on the incoming tides

CHAPTER 4 SUMMARY

■ All projects to restore the lagoon and protect the city mustwork in a symbiotic way

■ There are two kinds of measures:‘local’ measures within the cityand the islands, and ‘diffuse’ measures across the entire lagoonenvironment

■ Local measures offer vital opportunities to improve the city’sinfrastructure and restore its buildings

■ Some remedial measures are highly experimental and theireffects will only be learned in the long-term

■ Restoring the saltmarshes is key to the future health of theenvironment, its unique wildlife and the resilience of the entirelagoon system

■ Most scientific authorities are in agreement that the most viable way to protect Venice from extreme flood events is tocreate a barrier

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left The inlets aredemarcated by rockand concrete jetties

right A beach wasartificially built atPellestrina to givegreater defence againstthe sea

below right Pipelinesare used to deliver asand-and-water mixturefor beach replenishment

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Barrier

left Malamocco inlet, where construction of the breakwaters associated with the barriers officially began in spring 2003

THE mobile flood barriers to be built at the three inlets to theVenice lagoon have a single purpose, to protect the city andlagoon islands from major storm surge flooding. They arebeing developed against a background of intense scientificand political debate about whether they should take priorityover other measures, how viable they are, and what their likelyimpact will be on the life of the lagoon. The barrier design isradical and poses enormous engineering challenges. Researchwill continue as the gates are built and tested, as will researchinto their effects on the natural system of the lagoon. Lessonscan be learned from other flood barriers across the world, buteach barrier system and location is unique.

THIS CHAPTER EXPLORES■ THE CONSTRUCTION OF THE BARRIERS■ THEIR MECHANISM AND OPERATION■ THE COMPLEMENTARY MEASURES AT THE COAST AND INLETS■ OTHER BARRIER SYSTEMS■ THEIR PREDICTED IMPACT ON THE LAGOON SYSTEM■ DEBATES ABOUT THEIR ENVIRONMENTAL IMPACT

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“Building barriers and flood defencesagainst changing sea levels is an on-going

process. Barriers buy you time”Sarah Lavery, Thames Flood Defence Strategy 2100

The mobile barriers THE barriers will consist of 78hinged steel floodgates, stretchingacross the three inlets of thelagoon.The wider Lido inletbarrier (41 gates) will be in twoparts, separated by an artificialisland.The Malamocco (19 gates)and Chioggia (18 gates) inlets willeach incorporate a navigationallock for shipping.

The huge gates are 20m wide,up to 5m thick and between 18 and 28m in length (depth).They will be anchored at onehinged end to concretefoundations sunk into the lagoonbed. They will lie unseen on the bed, filled with water, until astorm warning comes, when they will be pumped full of airand rise to form a wall againstthe sea. They will remain up for the duration of the surgetide, and will then refill withwater and sink down again.

The construction of thebarriers is a major engineeringfeat, not just to design a complexmechanism that will continue to work reliably for decades, butalso to manoeuvre the hugepanels into place without erroror technical hitches.The materialsused must withstand the harshconditions of the saline waters.

The proposed mobile barrier.Design modifications, even duringconstruction, are a common andexpected part of sophisticatedengineering work, and the final designis likely to vary slightly from thisspecification, first published in 1996

Location of barriers at inlets

How the individual panels will rise and fall

Lido

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THE idea of a system of gates between the lagoonand the Adriatic Sea is not new – a scheme waseven proposed in the 17th century. But the needfor protection came sharply into focus after the1966 flood and in 1971, a ‘competition of ideas’was held. The concept that won was for an under-water mobile barrier.

It took more than a decade for an institutionalframework to design, assess and start to build thebarrier to be put in place. The 1984 ‘Special Lawfor Venice’ led to the creation of the ConsorzioVenezia Nuova (CVN), a consortium of large Italianengineering and construction companies, whichwas charged with implementing the solution tothe ‘water problem’ (for details, see Appendix).

Twenty years of planning, technical develop-ment and testing followed, amid intense scientificand political debate. The final go-ahead to plan andbuild the mobile barriers was given only in 2001,and work began in earnest in 2003 with the con-struction of an outer breakwater at Malamocco.

The first experimental prototype, calledMOSE (MOdulo Sperimentale Elettromeccanico)was built and tested between 1988 and 1992. Ithas given its name to the larger scheme – the com-plete set of mobile barriers and ‘complementarymeasures’ at the inlets.

MOSE is being developed under a set of con-straints imposed by the Comitatone (see Appen-dix), deriving from environmental assessments inthe late 1990s and pressure from the Port ofVenice and industry concerned by the possibilityof disruption to their transport links. The barriersmust have little or no negative impact on naviga-tion, nor on lagoon flushing and water quality,ecology and habitats, or on the ‘aesthetics’ of thelagoon. The latter is a key reason for the underwa-ter design solution.

The project is being developed throughdetailed engineering studies, physical modellingand computer simulations to explore how the bar-riers will work in situ, how they should be man-aged, and to assess their impact on water flow inthe lagoon. This work must be integrated with,and be informed by, scientific studies on the

lagoon’s physical and biological functioning, aswell as research to improve weather forecasting. Itis remarkable that an enormous amount of datacollected by numerous institutions (but mainlythe Venice Water Authority) has not been circulat-ed or made readily accessible to the scientific com-munity nor the public at large. This has obstructedthe comparison of research results and findingsfrom different modelling approaches and thedevelopment of a non-ideological, constructive,science-based debate on certain key issues.

FLOOD ALERTWhen water levels of more than 110cm above thereference level are predicted, the mobile barriers

will be put into operation and stay in place for thelength of the tide surge. On flood alert days, thelagoon will be cut off from the Adriatic Sea for anaverage of five hours at a stretch (longer if there arecontinuing surges in the following days as was thecase in 1966). The imperative is to close the gatesat the right time, for the shortest time possible.

Deciding when to close the barrier is a complexmatter, as not only the tide affects water levels inthe lagoon but also the weather (the atmosphericpressure, winds and rain). Some water will stillflow into the lagoon even when the gates are up,and heavy rains will also bring water into the sys-tem. In this case, the gates must be activated whensea level is still relatively low to allow a margin forinternal water level rise. Winds can drive highwaves across the lagoon, meaning that water levelsmay be higher in some areas than others.

A reliable model is therefore essential to pre-dict and guide barrier closure decisions. Presentsimulations can result in 50 percent ‘false alarms’and more research will be needed to improveaccuracy.

PROPOSED MODIFICATIONS AT THE THREE INLETSThese diagrams show the position of the barriersand navigation locks at the three inlets. The MOSEscheme is required to reduce the inflow of waterfrom the Adriatic Sea by between 15 and 28 per-cent at the inlets. To achieve this, the complemen-tary measures – moon-shaped (lunate) breakwaterswill also be built beyond each inlet. The Malamoc-co outer sea wall is about 1,300m long and 3–4mabove mean sea level; at Chioggia it will be abouthalf as long and 2.5m high.

The Malamocco breakwaters will be completeby the end of 2004 and work is beginning atChioggia. The Lido breakwaters are still at thedesign and approval stage. At the same time, thechannels through the inlets will be reduced indepth and their profile will be changed. Someengineers believe that these changes will helpincrease resistance to the flow of water in and outof the lagoon, and so further reduce the volume ofwater entering from the Adriatic Sea. Otherhydraulic engineers expect the benefits to beslight, and the key issue is cost effectiveness. Thereis also concern about the long-term ecological andwater quality impacts of these changes.

WHAT WILL HAPPEN TO TANKER TRAFFIC?The navigational locks allow shipping to continueundisturbed by gate closure, except where stormyweather prevents them coming into port anywayand large ships may find it more difficult to steerpast the breakwaters and through the new locks.But computer simulations have shown that it willbe possible. In the future oil tankers may not haveto come into the lagoon – there have been propos-als to locate an oil terminal out in the Adriatic Seaand link it to the port via a pipeline, removing thethreat of an ecologically disastrous accidental spillin the lagoon.

“This type ofproject requires a highpercentage ofunusual workand advancedtechnology.” Alberto Scotti, barrierdesign engineer

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How will the barriers work? Lido inlet800m wide, 12m deep,two barrier systems anda central island

1 boat haven2,4 Barriers3 artificial island 5,6 existing jetties7 breakwaters

Malamocco inlet400m wide, 16m deep

1 Barriers 2,4 existing jetties3 navigational lock 5 breakwaters

Chioggia inlet380m wide, 10m deep1 boat haven2,4 existing jetties3 Barriers 5 breakwaters

above Engineeringinterventions at the inlets were alsoconsidered 400 years ago

below A physical modelof the lagoon is used toinvestigate the systemand the barrier impacts

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Barrier

FLOOD barriers protect many vulnerable cities inEurope. The three examples given here – fromLondon, Rotterdam and St Petersburg – highlightsome of the experience that Venice can benefitfrom, although the context and tidal systems differmarkedly and every situation bears a certainuniqueness. Each project was set up to protectmajor cities and other areas of dense populationfrom sea storm surges, and each scheme chose acompletely different barrier system.

In two cases, there was serious conflictbetween environmental impact and the desire toprotect the urban population. In all cases, majorsocial and economic issues were at stake. A bal-ance always has to be struck, a trade-off betweenprotection, trade and environment. Everyone alsohas to recognise the scale and uncertainty of thesegrand schemes, where whole ecosystems are dra-matically changed – indeed, in the Dutch case,altered beyond recognition from salt to freshwater.Research cannot stop when the barrier is built; theconsequences of our actions need to be under-stood, so that we learn for the future.

In summary, the lessons to be learned are that:

■ Flood disasters are commonly a trigger for action■ There needs to be a general public and political

will to drive the project forward – often it is onlycrisis that focuses people’s attention

■ Major engineering schemes are expensive, experi-mental and difficult

■ Funding needs to be secure – half-completedschemes pose environmental hazards in themselves

■ Barriers cost a lot of money to operate and maintain

■ High-tech barriers need skilled people to runthem, not just to build them

■ Design modifications are normal as engineerslearn more about how a barrier will perform onceinstalled, and what impact it will have

■ There will inevitably be a trade-off between safetyand environment, the skill is to find a way ofworking together, rather than in opposition

■ In a changing world, barriers are never a finalsolution – cities have to keep planning for the following 100 years

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Learning from other schemesThe successes and failures of other schemes have valuable lessons to teach Venice.In turn,Venice’s experience will inform other schemes

The Thames Barriersystem is now also usedfor management of riverflooding – an unforeseenapplication at the time of construction

left Other Europeanflood barriers1 Thames Barrier2 Rotterdam Waterway3 St Petersburg

1 2

3

THAMES BARRIER, LONDON,ENGLAND

The River Thames runs through a densely popu-lated and commercially sensitive floodplain,including the City of London, and flooding has thepotential to cause economic and social disaster.Surge tides from the northern Atlantic are forceddown into the North Sea, driving extra water upthe river and occasionally flood defences are over-topped. Plans to protect the city were triggered bya disastrous flood in 1953, which killed 317 peo-ple in England and Scotland.

The chosen barrier scheme consists of a series

of rotating (normally submerged) gates suspend-ed between a series of towers. Construction start-ed in 1974 and the barrier opened ten years later.London now has one of the best tidal defences inthe world, designed to cope with storm surgesand estimated sea level rise well beyond 2030. Butclimate change is predicted to bring higher seasand uncertain changes in storminess, and plan-ning has already begun for the ‘next generation’ ofprotection up to 2100.

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Learning from other schemes continued

ROTTERDAM AND THE EASTERN SCHELDT,HOLLAND

Holland is particularly vulnerable to flooding,some 60 percent of the land being below sea level,so flood defences are critical. Just as in England,the decision to embark on large-scale storm andflood defence systems to protect the area aroundRotterdam was taken following the disastrous1953 flood, in which 1,835 people died in Hol-land. This led to the ‘Delta Plan’ to reinforce thedikes and to close many of the existing estuarieswith dams.

Only two of the estuaries were left open: theWestern Scheldt estuary, which leads to the Portof Antwerp, and the New Waterway, which is theentrance for the Port of Rotterdam. For the NewWaterway, a barrier project was started in 1991,and just six years later the Maeslant barrier wascompleted. This barrier is almost as wide as theEiffel Tower is high. Giant swivel gates swingacross the estuary to form an impenetrable wallprotecting one million people.

During its construction, the engineeringdesign had to be revised when the team realisedthat ‘seiches’, long waves with a period of 15–90

minutes and with amplitudes of over 2m, couldcreate a negative head over the gates, which wereinitially not designed to resist them. Seiches arealso a feature of the Adriatic, and the Venice gateswill have to cope with them.

The Delta Plan brought about considerablechanges in the tide and the ecosystems of thearea. In some areas the decision was made tochange the ecosystem completely from a saline tofreshwater environment. At the Eastern Scheldt,there were furious protests culminating in a seabattle pitting environmentalists and fishermenagainst visiting politicians. A much more expen-sive system resulted, incorporating a storm surge barrier.

The Maeslant barrier has now been operatingfor seven years, and has yet to be closed for a surgeemergency. But it is tested yearly, just before thebeginning of the each storm season, to check itstill works. Dutch experts stress the importancebut difficulty of maintaining highly skilled teams,who are used to the demands and vulnerability ofsuch a high-tech system.

ST PETERSBURG,RUSSIA

Like Venice, St Petersburg is a major port, and oneof Russia’s greatest architectural treasures. Thecity is in a low-lying coastal plain where the Nevariver discharges into the Gulf of Finland. Much ofthe old city lies little more than 2.5m above thesea, and floods have been part of its history – thegreatest in 1824 when waters rose nearly 4mabove normal levels.

Plans to build a 24km flood barrier across theNeva Bay began in the 1960s. Construction start-ed in 1980, but work halted in 1990. There wasalso huge local and international opposition to thescheme, based on the fear that the ecology of thebay and the Gulf of Finland would be seriouslydamaged by the system. The shallow waters areinternationally important breeding grounds forfish and feeding grounds for migrant birds.

Extensive studies have since showed that thebay is already suffering serious environmentalproblems due to pollution from the city and industry. Large-scale field experiments have sincedemonstrated that the gates could be used tochange the water flow in the bay, to help ratherthan damage the ecology. This has also been dis-cussed in Venice.

In 2002, the scheme restarted when a consor-tium of international banks agreed to supportcompletion of the flood defence project. A publicconsultation exercise on the environmentalaspects of the scheme resulted in both an imp-roved feasibility study and increased local supportfor the barrier. The barrier should be completed infive to seven years.

The Maeslant defences are controlled by asophisticated computersystem

Initial attempts to buildthe barrier suffered frompoor public consultation

reorganisation, notably the proposal to move thepassenger port to outside the Lido inlet, whichwould allow greater flexibility in re-dimensioningthe inlets.

ISN’T THERE A BETTER WAY OF SPENDINGALL THIS MONEY?Some opponents argue that the money spent onthe barriers would be better spent on the other dif-fuse and restoration measures described in the lastchapter, and that these ‘alternative’ measures willbe enough to protect the city. However, carefulanalyses and computer simulations show that thediffuse measures would not have a significant effecton high waters, nor would their combined effectreduce levels by more than a few centimetres. Theycertainly could not provide the protection neededto cope with a storm surge like that of 1966.

While not all scientists are confident that theradical design chosen for the barriers is the rightone, most are convinced that, if flood protection isthe immediate priority, then flood barriers must bebuilt now. For them, the barrier is the only way ofprotecting the city and lagoon from future floods.Alongside this, the lagoon will continue to becomea bay despite the barriers – so other works areneeded to combat the erosion and associated eco-logical problems.

WHAT EFFECT WILL THE BREAKWATERS HAVE?Some scientists claim that it is not the barriers thatpresent the problem, but the lunate breakwaters –their effect on dissipating the inflow of the sea maybe fairly marginal plus they could create additionalsediment budget complications.

AREN’T THERE ANY OTHER SOLUTIONS?Many other barrier concepts have been proposedover the years, with varying degrees of professionalcredibility and feasibility testing. They includeplacing a number of smaller flood barriers at theentrance to the main island canals; installinginflatable rubber tubes at the inlets; and parkingold tankers filled with water at the bottom of inletsinstead of the fixed gates. Other ideas involve acombination of engineering and socio-economic

“Glory, if it succeeds,and graveresponsibility, if it fails, for everyone”

Local newspaper

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ONE of the most serious political challenges to theMOSE scheme has come from environmentalistsand their scientific supporters, who believe thatthe gates will have a very damaging effect on thelagoon. MOSE is now underway, but the questionsstill come.

HOW OFTEN WILL THEY HAVE TO CLOSE?At present, the barrier designers predict that thegates will operate an average of five times a year. Asstorms tend to occur in winter, most of these clo-sures will be concentrated in a few months. Thegates may stay closed for several tidal cycles whenthe storm surge is followed by echoing seiches.

ARE THESE ESTIMATES RELIABLE?The opponents argue that predictions of howoften the gates would operate are unrealisticallyoptimistic, as global environmental change isexpected to bring higher sea levels may increasefuture storminess.

HOW WILL THE LAGOON BE AFFECTED?The basic argument of opponents is that, when thefloodgates are closed, the lagoon will become aclosed basin, cut off from the beneficial effects oftidal flushing. The lagoon will also be cut off fromsediment exchange during a storm. Although westill do not know enough about the current role ofstorms in the net sediment transport for this sys-tem, it is possible that the barrier closure couldhave a positive effect on reducing sediment exportfrom the lagoon.

WHAT ABOUT THE WATER QUALITY?Without daily tidal flushing, ecologists fear thatthe water in the lagoon will stagnate and bottle up pollutants and nutrients. Fish and otherspecies could suffer, and the algal blooms thatplagued the lagoon in the 1980s could return. Thecounter-argument is that flushing will occur very quickly once the gates re-open – recent studies

have shown that much more water is exchangedbetween sea and lagoon on each tide than was pre-viously thought.

COULD THE GATES ACTUALLY HELP WATERQUALITY?Some scientists and engineers have even proposedthat the barriers could be operated, when notneeded for flood control, to stimulate flushing inthe lagoon. By opening and closing the gates insequence, for example, favourable water circula-tion patterns could be generated within the lagoonto aid flushing. However, it is also recommendedthat a correct solution is, after all, to tackle theproblems of water quality and pollution at source,such as providing a sewage treatment system forVenice, and not to look to the sea to solve them.

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Debates about the barrierThe key debates around the barrier scheme concern the possible impacts on the water quality andecology of the lagoon and the cost-effectiveness of the scheme. Some uncertainty prevails

left A prototype singlegate was tested near the Lido inlet – many peoplefeared that these redtowers were apermanent feature,and there were hugeprotests when theprototype was first seen in Venice

“If I had tochoose betweenthe Port orVenice, I would choose Venice”

Claudio Boniccioli,former President of the Venice PortAuthority

A summary of interventions The scale of the projects underway to solve the ‘Venice problem’ is staggering. Their developmentneeds careful coordination, as each will affect the other

Extreme high tides (over 110cm)Mobile flood barriers at lagoon inlets

Deteriorting jettiesReconstruction of jetties

Medium to high tides (to 110cm)Local interventions to protect urban areasand embankments

Physical deterioration of lagoonRestoration, dredging and rebuilding features

Access closed to tidal flowRe-opening of fish farms and other isolated areas

Coastal erosionReinforcement, restoration of walls and beaches

Environmental damage and pollutionRestoration and prevention

Oil tanker traffic pollution risksNew terminal proposed for offshore

CHAPTER 5 SUMMARY

■ To protect against extreme flooding, construction has begun for the MOSE scheme ofmobile barriers and breakwaters at the lagoon inlets

■ Further measures are needed to reverse the degradation of the lagoon system, tocomplement and mitigate the negative impacts of the barrier system

■ Venice can benefit from experience gained in reducing flood risk in other places, notablyflexibility during implementation, institutional rigour and unexpected benefits/adaptationsof the system

■ This is a new phase for science in Venice, where some old questions are sharpened byimplementation of the barriers and many new questions arise

■ The long-term options for Venice will need to be considered in the context of uncertaintyover future global environmental change

Policy-makers aspire to the adoption ofinnovative,sophisticatedengineering solutionsalongside thepreservation oftraditional lagoonactivities

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HIGH waters and tides, erosion and pollution,physical and socio-economic deterioration -– themany risks and problems that face the Venicelagoon are intricately bound together. While eachrequires its own tailored solution, the problem canonly be solved if it is tackled as a whole.

Scientists and engineers are dealing with manylayers of uncertainty about the semi-natural sys-tem and the measures proposed to modify it.There is much that is not known, much to study,and each element of the chosen approach mustremain flexible, ready to respond and adapt to newknowledge. Meanwhile, the mobile barrier andother interventions are proceeding, from feasibilityto planning and final execution, always under con-stant review by all parties.

The success of the interventions will be meas-ured not just in technical terms, but also in terms ofthe wishes of many others. These include peoplewho live and work in the city, those who depend onthe lagoon’s industry and port, those who visit thecity and those who treasure the lagoon’s ecosys-tems. All have a stake in Venice’s future.

Few projects, least of all those that involvecomplex environmental systems, have the benefitof perfect certainty and complete knowledge, butdecisions still need to be made and acted on. This is especially so for large-scale projects. Butsuch projects do provide an opportunity to learn:from actual impacts as well as during construc-tion, at different phases before the project is completed. Protecting the city from flooding isurgent. The barrier is not the final solution, but itbuys the city time.

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6

Futures“A future that we would like

to think has no end”

Bruno Dolcetta, President, Insula SpA

left St Mark’s Piazzetta, with the landmark statues of St Mark and St Theodore,flanks the open lagoon

TO most people, a world without Venice is unthinkable, butas the previous chapters have shown, saving the city is adaunting task. It needs the concerted efforts of everyone –politicians, scientists and engineers, every citizen and theinternational community – to succeed. There are many possible futures for Venice, serving different interests andrival demands, which must be made explicit, prioritised andreconciled. Good science is the bedrock for any lasting solution, but in the end it is up to the people who live inVenice – and also all who love it – to answer the question,‘what sort of Venice do we want?’

THIS FINAL CHAPTER LOOKS AT■ THE UNCERTAINTIES THAT FACE THE DECISION-MAKERS ■ THE ROLE OF SCIENCE IN MOVING FORWARDS ■ WHAT THE WORLD CAN LEARN FROM VENICE ■ WHAT CHOICES ARE AVAILABLE

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the city, based on the historical correlation of cer-tain winds and observed water levels in Venice.The other approach is deterministic – by setting upa model of what is known about the many parame-ters affecting tide levels, data for each of these isfed into the model, which then calculates theexpected water level on the basis of known interrelationships between the parameters. Thesesystems are crucial to the success of the barriermanagement scheme.

WIDER CONCERNS Mobile barriers may be able to protect Venice fromextreme floods, but much of the northern Adriaticcoastline is vulnerable to permanent flooding.Venice is enormously privileged – less famousplaces, lacking its high international profile, willprobably not be helped.

“Sea level riseis like a ropethat istighteningaround the neck of Venice”Alberto Tomasin,Dept of AppliedMathematics,Università Ca’ Foscari, Venice

THERE is substantial agreement among interna-tional scientists that human-induced climatechange is a reality, and that it will lead to increasesin average sea level and changing weather patterns.Currently available estimates of future changes aremainly global averages and, to date, there is littleagreement on the rate and scale of sea-level rise ona regional or local level. In addition to sea levelchange, regional weather patterns are being affect-ed and in Venice this could mean changes to theintensity and frequency of winds, surges, rainfalland indeed extreme events.

These uncertainties are bound to continue butmay be reduced as we develop a better under-standing of how the world’s climate systems work,based on detailed studies of present climate,analyses of past climate conditions and improvedsimulation of future scenarios. The associationbetween observed, measured changes and human-induced factors is still tenuous – because climateand sea level are both inherently variable andbecause there is a time lag between cause andeffect of climate processes. We have less than ahundred years of measurements since industrialactivities and pollution levels reached a globallysignificant level.

Climate scientists liaising through the UnitedNations’ International Panel on Climate Change(IPCC) show that global sea level rise could be any-where between eight and 88cm by 2100. TheIPCC is now making a special effort to establishthe likelihood of the various levels within that widerange of possibilities. Their predictions are basedon data up to 1998, but more recent measure-ments of glacial melting already question some ofthe scientific assumptions used in the generalmodels. Others challenge the economic assump-tions about industrial development and the associ-ated amount of atmospheric emissions. So therange of possibilities to plan for is very wide.

Sea level trends are particularly hard to compare due to lack of uniformity in tide gauge

systems around the world and the fact that mostgauges are in coastal regions (and therefore affect-ed by local variables). Satellites have recentlybecome available for measuring sea level, espe-cially in the open sea, which is extremely useful.Readings for the Mediterranean are available forthe past eight years and show a rise of2.2mm/year overall – in the eastern Mediter-ranean, however, the rise is as much as9.3mm/year while in the Ionian it is falling by11.9mm. It has remained more or less level in the western Mediterranean and in the Adriatic.But even if the trends are unclear and the signalsthey give are conflicting, the growing understand-ing of how the Earth’s climate system works andinteracts with the oceans point in the direction ofunprecedented rates of change and a greaterchance of unpredictable catastrophic weather-related events. Oceans and ice sheets are so vast,they are still reacting to climate changes thatoccurred in a more distant past; researchers havealso shown how rain, wind and atmospheric pres-sure can influence relative sea level by as much as+/- 1m by their natural variations.

LOCAL UNCERTAINTIESAt a local level, uncertainty is even greater,although the positive link between average sealevel and flooding frequency has already beenmade (see Chapter 3). The possible sea level rise

for Venice is in the region of 12.6–70cm by 2100,according to a broad literature review. Besides thegeneral sea level rise and the continuing role ofsubsidence, it is imperative to better understandthe local conditions that affect not only sea levelrise but weather patterns. Changes in the frequen-cy and magnitude of storm surges that causeflooding in Venice is an expected consequence ofclimate change – but in Venice no trend hasemerged yet. Storms could become more frequentand/or stronger, or fewer but more intense.

Associated with this, Venice is constantlyimproving its ability to predict high waters withgreater accuracy on timescales of hours and days.Two models are used – one based on a statisticalapproach, which means that the model tells itsoperator the likely water level in response to datafrom weather systems moving in the direction of

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Venice and global warmingClimate change may pose the most serious threat to the long-term survival of Venice as sea level continues to rise

Storm waves overcomethe sea walls during the flood of 1966. Will Venice suffer more, orfewer, storms in thecoming years?

left St Mark’s Piazzettabecame part of the open lagoon during the 1966 flood

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IT is unrealistic to expect science to provide sim-ple, clear answers about such a complex, dynamicsystem as the Venice lagoon – partly because sci-entists do not know enough about how the lagoonsystem works. There is a huge amount of work todo to understand key physical dynamics, how var-ious physical and biological components interact,let alone to predict how their relationships willchange once the barrier and other restoration anddefence elements are in place. Each change willripple through the system, affecting all the otherfactors. Adaptation takes time.

The challenge is an exciting one, with implica-tions well beyond Venice, and well beyond sci-ence. The Venice lagoon is a natural laboratory forstudying the impacts of global, as well as local,changes on a coastal ecosystem and the lives of itspeople. Even after more than 35 years of intensivefield research, theoretical advances and imple-mentation of extensive safeguarding measures,the open questions regarding the Venice lagoon

system have changed little – as our knowledgedeepens, so does the detail required.

THINKING BEYOND THE BARRIERThe barriers are designed to protect Venice fromflood surges of more than 110cm above the refer-ence water level. The calculated closure scenariosincorporate a sea level rise of 16–25cm, whichwould bring the expected number of annual closures from seven to 39 times. The barrierscheme’s Environmental Impact Study stated thata 50cm increase in sea level was not considered,as it would be catastrophic not just for Venice butfor the entire world. The barrier designer’s cost-benefit analysis gives the project an expected life-time of 100 years or less. Thus the mobile barriersare not a complete or final solution, but theycould give Venice some more time. If all goes well,and the fears for the lagoon’s ecology are notrealised, the barrier will not significantly alter thebasic character of the lagoon during its operatingyears. But the city will continue to sink and waterlevels will continue to rise.

RADICAL IDEAS?In the 1970s a project investigated the viability ofraising Venice, building by building, out of harm’sway – by injecting materials underground to pushit upwards. A trial on one of the small islands inthe lagoon, Poveglia, revealed the heterogeneouslydistributed and highly variable ground layersbeneath Venice and the instabilities that could becaused by differing responses to the injectionswithin a single building or even adjacent ones.Recently the concept has re-emerged in a far moresophisticated and technologically advanced form.

The injection of sea water is being proposed ata depth of 600–800m via a series of wells placed ina 5-km radius around Venice. The aim, this time, isto uniformly raise a large area of the lagoon and thepotential is a gain in height of 30cm relative tomean sea level. It will take a few more years to

Science and uncertaintyIn predicting and adapting to the future of the lagoon we have to accept uncertainty as a reality that must be managed

far left Much of the Po Plain and other areas on the mainland in the Venice region are nearly at sea level or below it

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“The lagoon system and its dynamics represent the perfectlaboratory to develop an approach in which scientific, technologicaland economic factors interact and influence each other. If we canfind a solution to our problems in Venice then it might be possibleto apply that solution elsewhere in the world”

Pierpaolo Campostrini, Director, CORILA

investigate the feasibility in greater detail – particu-larly as the geological composition below Veniceand its lagoon and distribution of different types of soil down to nearly 1km from the surface haspresently only been characterised in a couple ofpoints. Even in the event of promising indications,the technique must first be tested in a pilot well. Ifit works, Venice would have several more decadesin its fight against sea level rise and increasinglyfrequent ‘chronic’ flooding.

Alternatively, Venice could look to the Dutchexample in the Eastern Scheldt, where an area waspermanently closed off from the sea and trans-formed from a saline system to freshwater. Asidefrom the biodiversity implications of losing manyplant, invertebrate, fish and bird species, pollutioncontrol would be a major issue – including areduction in contaminating inputs from the water-shed. Equally essential would be the implementa-tion of a complete sewage collection and treatmentsystem for the historical centre and other inhabit-ed areas of the lagoon.

At the opposite extreme is the option to acceptthe forces of nature and let the lagoon develop nat-urally into a marine bay, creating other, differenthabitats, and essentially relinquishing the city tothe waves.

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“If there is onething thatresearchers doagree on, it isthat the gatesare not the solesolution.” The Economist, September 2003

carefully. It is also important for Venice to settle itsrole within the context of the ‘metropolitan city’,including Mestre and other associated mainlandsettlements.

FOR TRADE,INDUSTRY AND AGRICULTURE?

Each has been targeted as villains in Venice’s story,and there are increasingly tight restrictions ontheir waste, run-off and emissions. Time bombsfrom the past still rest in the sediments of thelagoon as well as the many hectares of abandonedindustrial areas earmarked for remediation meas-ures in Marghera. But the industries that clusterround the port are vital parts of the economy,bringing wealth to the region and employing thou-sands of people. To what extent must Venice learnto live alongside these economically indispensablesectors? How much can the lagoon absorb withoutfurther damage? Would an offshore oil terminalreduce the risk of tanker pollution? Can alterationsbe made to the burgeoning growth in passengertraffic aboard gigantic cruise liners that pass rightthrough the heart of the city and deliver yet more‘bite and run’ tourists, as they are now called?

“Venice is oneof the mostconsistent andcontinuousexamples ofpermanenturbanplanningaffecting bothsettlement andenvironmentknown tohumanity”

Territorial Plan for Conservation and Development of the VenetianEnvironment andSettlement System(1995)

IN nature, lagoons are ephemeral, but in the histo-ry of Venice, man has actively maintained the sta-bility of the system and its ‘natural’ dynamics. Theenvironment and culture of Venice and its lagoonhave co-evolved and maintained each other formore than ten centuries, and they will always haveto be managed in some way. The question is, howis it best managed, and for whom?

Venice excites huge emotions. Each interestgroup sees the city and lagoon in different ways,valuing some attributes above others. It is perfectlypossible to make deliberate choices about thedirection to go in – whether, at its most radical, toreturn the lagoon to the sea (or to land), lettingnature finally take its course, or to take the neces-sary measures to maintain the precarious balancethat exists today.

The various institutional roles are outlined inthe Appendix – the Venetian district is charac-terised by a large number of authorities with over-lapping competences (many of which possess thepower of veto) resulting in a substantially weak-ened planning system with divided authority andrestricted impact. Scientists therefore have anespecially important role. By sharing data andworking across disciplines, they can be calledupon to clarify the present situation and futurescenarios so that it is possible to make deliberatechoices in the face of competing demands on thedelicate city and fragile lagoon.

WHAT IS VENICE BEING SAVED FOR?FOR NATURE? Any consideration of the future ofVenice must guarantee the conservation of thisunique system. Revitalising the lagoon’s physicalstructure and associated biological communities isessential. Further work is necessary to properlyappreciate the potential of lagoon-wide measuresto mitigate water levels and the impact of these(both positive and negative) on other aspects of thelagoon’s ecological balance. On the global stage,too, the preservation of endangered wetlands is an

international priority of increasing urgency. But what sort of restoration is acceptable, and

to whom? The new projects are not returning thesystem to its prior state, but creating a differentbalance of nature (including the increase of someaggressive grasses and bird species that are morecharacteristic of the mainland). It must be recog-nised that there is no single reference condition towork towards in rehabilitating the natural environ-ment and dynamics of the lagoon. Interaction overcenturies of human intervention, along with therelative influences of rivers and the sea, have pro-duced a mosaic of differing geographical and func-tional circumstances, each requiring its ownrestoration criteria.

FOR VENETIANS? With worsening flooding, struc-tural decay and pollution, matched by increasingcosts of living and buildings maintenance – prob-lems exacerbated by market distortions caused bymass tourism – Venetians are deserting their city.How will they be persuaded to return? Repairingthe city fabric, making it fit for the 21st century –the essential infrastructural works, restoring aban-doned buildings – could all make it worthwhile.Policy measures are needed to stimulate tradition-al as well as post-industrial productive activitiesand reduce the concentration on tourism mono-culture. Aside from the obvious socio-economiceffects of the ‘international mass consumption’ ofVenice, tourism damages the already precariousurban and natural environment. The effects(intense boat traffic, litter) are evident along themain thoroughfares of the city and are beginningto spill over into the lesser-known more fragileareas, such as the northern lagoon. The lagoon,too, is a place of work for Venetians – as the watersreturn to health, so can fishing be competitivelymaintained, balancing economic demands withthe needs of the ecosystem for long-term sustain-ability. But tourism, along with the port, is Venice’sprincipal earner so any adjustment needs to made

FOR THE WORLD? Venice is a UNESCO WorldHeritage Site: people all over the world feel theyhave a stake in its future, too. But does that meanVenice is obliged to allow itself to be consumedby tourism, and are tourists merely supportingthe preservation of a fossil? A review of the crite-ria that put Venice on the list of World HeritageSites carries some important reminders – in addi-tion to Venice’s unmatched artistic, architecturaland cultural development and influence aroundthe world, it is an outstanding example of wet-land biodiversity and “symbolises the victoriousstruggle of mankind against the elements, andthe mastery men and women have imposed uponhostile nature”.

Venice has the potential to be a powerful casestudy in sustainable social and economic devel-opment, leading the world in learning to live withnatural systems in more harmonious ways, ratherthan trying to dominate them. The scientificcommunity recognises that the answers they canprovide are only part of the final equation. Buttheirs remains a vital voice.

“It is adelicate task to get peopleto worktogether at the bottom ofthe pyramid,where the realwork getsdone!”

Dr RobertoFrassetto, founderCNR Institute for the Study ofLarge Masses

What future does Venice want? Tackling complex environmental problems is not only a matter of finding scientific and technical solutions.It is also important that people have the political will to solve them, and the financial means to do so

above, left to rightSan Giobbe housingproject. A Venice in PerilFund initiative to demonstrate thefeasibility of traditionalbuilding techniques forthe restoration of popular housing in Venice.Marghera.Venice full of touristsright Sea walls at the Lido

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CHAPTER 6 SUMMARY

■ Human-induced climate change poses one of the biggestlong-term threats to the survival of Venice – sea level could rise locally by at least 8cm and as much as 70cm by 2100

■ Predicting sea level rise is extremely complex and there is much uncertainty regarding the scale of impact it will have,also depending on adaptation and mitigation measures

■ Radical ideas for saving the city include raising the ground level by up to 30cm

■ The future health and survival of the city and lagoon depend on creating a balance between the needs of the environment,industry, agriculture, tourism and the Venetians

■ Scientists need to work better among themselves as well as tosupport greater stakeholder interaction if sustainable policiesare to be developed

SPECIAL LAWS FOR VENICE

During Venice’s time as a Republic (607–1797),there were carefully specified and vigilantlyapplied laws for the lagoon and mainlanddomains.This attention dwindled from the 19thcentury onwards and consequently the lagoon’sdefining characteristics and underlying dynamicsaltered significantly. Only following the 1966disaster was care taken again for the specialcharacteristics of the lagoon and its inseparabilityfrom safeguarding measures for the unique city.

While ordinary laws set the duties of the Stateand local authorities as regards territorialmanagement, the Special Law of 1973established that Venice is of pre-eminent nationalinterest and gave the State authority todetermine specific objectives and associatedfinancing for measures.The main objectives ofthe first Special Law were:■ Safeguarding of the environment (landscape,

historical, archaeological, artistic features);■ Protection of the hydraulic and

hydrogeological equilibrium;■ Regulation of watercourses (natural and

artificial) feeding into the lagoon;■ Reduction, followed by regulation, of tide

levels;■ Coastal defence works;■ Pollution protection works.

Another iteration of the Special Law in 1984 hada slightly different orientation. It committed theState to the design, experimentation andexecution of works to:■ Re-establish the hydrogeological equilibrium of

the lagoon;■ Arrest and invert the process of degradation;■ Protect the insulae;■ Protect the urban settlements from the

exceptionally high tides, “also via measures atthe inlets (...), with the characteristics ofexperimentability, reversibility andgradualness”.

The law also allowed the Public Works Ministryto identify a single operating agency to guaranteethe “unitary nature” of the interventions forsafeguarding the lagoon. Consorzio VeneziaNuova, made up of a group of Italianconstruction and engineering firms, wasnominated as the executive body – essentially aprivate company with public objectives.The 1984Law also established the Comitatone (seebelow) to oversee the implementation ofsafeguarding objectives and budgetary allocations

the physical and environmental safeguarding ofthe lagoon ecosystem in a unitary and organicfashion and with a systematic approach.

Measures to monitor and improve the qualityof water and sediment in the lagoon – mostrecently known as the MELa Programmes 1 and2 – are also the responsibility of the State andcarried out by CVN, in collaboration with theRegione, ARPAV and university researchdepartments.

■ Regione Veneto – Regionaladministration

www.regione.veneto.it Pollution abatement within the lagoonwatershed area is the responsibility of theVeneto Region, which has established aframework programme of measures to monitorand reduce pollution in the drainage basin,known as the Master Plan 2000. Pollutionabatement and prevention measuresprogrammed by the Veneto Region for thedrainage basin to reduce the loads arriving inthe lagoon are now closely coordinated withlagoon water quality control measures (theremit of MAV/CVN).

The Regione is also responsible for drawingup the territorial plan for the conservation anddevelopment of the Venice environmental andsettlement system (PALAV). It covers 16municipalities from three provinces (Padua,Treviso and Venice). It was requested under the1973 Special Law – it took over a decade toformulate, underwent several iterations and wasfinally approved in 1995.

■ Provincia di Venezia – Provincialadministration

www.provincia.venezia.itThe Provincial Administration does notparticipate in the Comitatone, except on aconsultative basis, although it oversees certainkey elements of Venice’s natural resources, alongwith about 40 other municipalities within itsdomain. It has some land use management andenvironmental protection responsibilities, notablyregulating fishing activities in the lagoon as wellas hunting licences and it runs theenvironmental police department. It overseesthe protection of flora and fauna, natural parks,organises waste disposal at the provincial leveland controls effluents and emissions and noisepollution.

It is responsible for certain restructurings andrestorations financed by the Special Law(notably schools and the island of San Servolo);territorial planning including landscapeprotection and environmental resources;planning and environmental education forpollution prevention and control. A small area ofthe Venice lagoon falls within the domain of theProvince of Padua.

■ Comune di Venezia – Venice Municipality www.comune.venezia.it The Venice Municipality governs the main urbanareas of the lagoon – the historic centre of Venice,Lido, the islands of Murano, Burano, Mazzorbo andTorcello, and the coastal strip of Pellestrina and SanPietro in Volta in the southern lagoon, as well asMestre and Marghera. (About nine othermunicipalities have territories within the lagoonand are duly subjected to the special legislation for Venice.)

In the context of the Special Law, the Comunemust look after Venice’s historical, cultural,architectural and environmental heritage while alsoaddressing the socio-economic factors thatdetermine the city’s identity and wellbeing –everything from stimulating productive activitiesand controlling tourism to assisting young coupleswith obtaining affordable housing and providingcrèches for babies. Specifically, Special Law fundsare used by the Town Council for:● Acquisition, restoration and refurbishment of

buildings for residential, social and cultural,commercial and artisan uses – consideredessential to maintaining the socio-economicidentity of lagoon settlements;

● Basic infrastructure (street lights, utilities etc,) aswell as bridges, embankments and canals withinthe municipal domain, i.e. the 45km inner canalnetwork (whereas the larger canals are withinthe MAV remit along with the rest of the lagoonopen waters);

● Subsidies for restoration and maintenance works for private buildings, including for example the installation of lifts in tall palaces(pending approval of the SafeguardingCommission and the local branch of the cultural heritage ministry);

● Acquisition of areas to be converted toproductive activities and the associatedinfrastructural requirements.

The Comune set up a mixed company – Insula spA – for the integrated management of canaldredging, raising street levels, revision of utilitypipelines, underground maintenance works, etc.(see below).The tide forecasting office (CSPM –see below) is also part of the Comune. Executivesfrom the Comune set up a working group in 1999to review the Environmental Impact Study of themobile barriers.

among the various institutional bodies.Then in1992 the Third Special Law made it arequirement to obtain the opinions of theVeneto Regional administration and those of theVenice and Chioggia municipalities forsafeguarding strategies and measures. Its mainother points are:■ Adjustment and reinforcement of the long

breakwaters at the three lagoon inlets;■ Local defences from high waters for built

areas;■ Restoration of lagoon morphology;■ Halting the process of the lagoon’s

deterioration;■ Coastal defences;■ Substitution of petrol tanker traffic in the

lagoon;■ Opening up of the closed acquaculture areas

to tidal expansion.

As well as setting out the safeguarding objectives,each Special Law also set aside State funds forfulfilling them. Since there has not been a SpecialLaw since 1992, Parliament has meanwhile setaside funds for safeguarding Venice in its annualbudget. But in 2003, for the first time, noprovisions were made for Venice in the budget,nor again in 2004. Funding for the mobilebarriers, however, has continued via the StrategicObjectives, a measure introduced to fund majorinfrastructural projects such as this and a bridgefrom the Italian mainland to Messina, in Sicily.

INSTITUTIONAL FRAMEWORK

Management of Venice and its lagoon isnotoriously complex. Indeed, the lack of progresson implementation of a robust plan forsafeguarding measures has been attributed tooverlapping and fragmented institutionalresponsibilities among various administrationsand even within departments of a single entity.Venice is the capital of the Veneto Region innorthern Italy and of Venezia Province, one ofthe region’s seven provinces. National ministriesand regional, provincial, and local authorities, aswell as the Venice City Council, are allresponsible for various aspects of theadministration of the city of Venice, its lagoon,and the surrounding areas. For example, the landthat drains into the Venice Lagoon, an area ofalmost 1,900 km2, is administered by 100 localauthorities.

The 1973 Special Laws assigned specificresponsibilities to various authorities concernedwith safeguarding Venice and the lagoon.TheItalian State has responsibility for the physical

especially how to divide the budget.Thecommittee is chaired by the President of theCouncil of Ministers (the Italian Prime Minister)and consists of the heads of five ministries, theirexecutive branches and the various localadministrations, including the President of theVenice Water Authority (Secretary), the Ministerfor Infrastructure and Transport, the Minister ofthe Environment, the Minister of CulturalHeritage, the Minister of Transport andNavigation, the Minister of Universities andScientific and Technological Research, thePresident of the Veneto Region, the Mayor ofVenice, the Mayor of Chioggia and tworepresentatives of the many other localauthorities bordering the lagoon.

■ Magistrato alle Acque (MAV) – VeniceWater Authority

www.magisacque.it The Venice Water Authority is a technicalagency of the Ministry for Infrastructure andTransport with direct and primary responsibilityfor the safeguarding, security and hydraulicprotection of a large area spread across anumber of regions (Veneto, Friuli andLombardy). It was established in 1907 but thename dates back to an organ of the VenetianRepublic of the same name, founded in 1501.

MAV duties cover five national rivercatchments (Adige, Brenta-Bacchiglione, Piave,Livenza,Tagliamento), one internationalcatchment area (Isonzo), and the lagoons ofVenice, Marano and Grado.With regard to the Venice lagoon, MAV carries out systematicmonitoring activites and oversees the planningand execution of safeguarding measures viaConsorzio Venezia Nuova, its executive agency.A few technical offices have remained withinMAV, notably the Anti-pollution Service,which publishes a monthly digest of lagoonwater quality according to a series of physical-chemical characteristics at five monitoringstations.

■ Consorzio Venezia Nuova (CVN)www.salve.it The Consorzio Venezia Nuova is the executiveagency of the Ministry for Infrastructure andTransport – Venice Water Authority (asestablished by the second Special Law)responsible for planning and implementing themeasures to safeguard Venice and its lagoon,delegated by the law to the State.

The second Special Law established that asingle body could take on responsibility for theinterventions as a whole, on behalf of andcontrolled by the Venice Water Authority, andon the basis of a general plan of interventionsdefined and approved by the Comitatone (andtherefore by the institutions represented on thecommittee) and by Parliament. Hence CVN isrequired to prepare and implement an‘integrated plan’ to tackle the various aspects of

safeguarding and restoration of thehydrogeological balance in the lagoon.TheVeneto Region is responsible for the abatementof pollution, especially from the drainage basin.And the city councils of Venice and the town ofChioggia at the southern end of the lagoon areresponsible for urban conservation andmaintenance, as well as activities aimed atpromoting socio-economic development.

The Venice Water Authority (Magistrato alleAcque), which was founded in 1501, hasresponsibility under the Italian Ministry of PublicWorks for ensuring the survival of Venice, itslagoon, and the living species that inhabit it, andfor protecting the lagoon from both naturalevents and human impact.

In 1992, a general plan backed by law toimplement measures designed to safeguardVenice was launched by the Venice WaterAuthority and the New Venice Consortium.Theplan is two-pronged.The first prong relates tothe protection of the city from high water levelsand flood damage by improving its physicaldefences by, for example, raising embankments,and also by reinforcing the coastline to protect itfrom storm damage.

The second prong aims at improving theenvironmental quality of the lagoon through aseries of interventions that tackle the factorscausing the deterioration of the lagoon’secosystem, and that also reconstruct andmaintain the natural environment of the lagoon.

■ Commissione di Salvaguardia –Safeguarding Commission for Venice

Instituted by the First Special Law, this committeewas granted authority to express itsdiscretionary opinion on all building works aswell as territorial transformations andmodifications planned by private and publicbodies everywhere within the Venice lagoonboundary.There are about 20 members,including UNESCO and the National ResearchCouncil (CNR), presided over by the Presidentof the Region.To some extent it overlaps withthe Town Council’s land use planning remit and ithas been accused of causing bureaucratic delays.Decision-making parameters are dominated byaesthetic rather than technical considerations.

■ ComitatoneThe second Special Law (1984) instituted amixed committee of government ministers andlocal authorities, known as the Large Committeeor Comitatone. It decides strategy, coordinationand control of the implementation of allmeasures to safeguard Venice and the lagoon,

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Total State funds allocated via the Special Law(1984–2000): nearly €6 billion

* of which €17m has been used for research via theMinistry for Education, Universities and Research.

Public Works Ministry-CVN€2.2bn

Others* €0.5bnComune di Chioggia €0.2bn

Comune di Venezia €1.4bn

Regione €1.4bn

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● International Private Committees forthe Safeguarding of Venice

Following the appeal launched by the DirectorGeneral of UNESCO in 1966, over 50 privateorganisations were established in a number ofcountries to collect and channel contributions torestore and preserve Venice. Over the years, theInternational Private Committees have workedclosely with the Superintendencies ofMonuments and Galleries of Venice, throughUNESCO, to identify and address priority needs.Since 1969, they have funded the restoration ofmore than 100 monuments and 1,000 works ofart, provided laboratory equipment and scientificexpertise, sponsored research and publicationsand awarded innumerable grants for craftsmen,restorers and conservators to attend specialistcourses in Venice. Expenditure by the PrivateCommittees for the five-year period 1996–2000was well in excess of 5 million (about £3million).

■ Venice in Peril www.veniceinperil.org The instigators and funders of the CambridgeResearch Project.Venice in Peril is a registeredBritish charity that works for the safeguarding ofVenice, by restoration and by research into itsecological problems. It was founded after thegreat flood of 1966 and since then has restoredover 25 monuments and works of art in the city.It works as part of the international associationof private committees for Venice, which has thestatus of a Non-Governmental Organisation inoperational relations with UNESCO.

THE CAMBRIDGE PROJECT

“Flooding and Environmental Challengesfor Venice and its Lagoon – State ofKnowledge” (2001–2004)The mission is to promote the objective studyand review of information concerning keyaspects of the flooding and environmental issuesrelevant to Venice, in an international dimension.This project was set up at the instigation of andwith financing from the Venice in Peril Fund andrun by Cambridge University (Churchill Collegeand Cambridge Coastal Research Unit) withlocal support from CORILA: A series ofpreparatory workshops were held in September2002 and a four-day International DiscussionMeeting was held at Churchill College,Cambridge, in September 2003.The meetingused Venice as the focus for discussion of state-of-the-art knowledge and comparison withexamples from around the world:

The primary aim of the meeting was toprovide a forum for discussion. It broughttogether over 130 researchers and practitionersfrom a broad range of disciplines. Participantswere invited to illustrate key research resultswith self-criticism and to suggest realistic and

demonstrable ways of solving current problems.Specifically, the conference sought to:● identify and discuss the key issues facing Venice

and proposed interventions and solutions tocombat the flooding and environmentalproblems;

● provide a synthesis of sound scientific andtechnological research results;

● explore scale (global-to-local) and uncertaintyissues associated with predicting the impact ofglobal environmental change in Venice;

● continue to build a community of researchersfor issues related to the sustainablemanagement of coastal lagoon systems usingVenice as a case study.

This initiative, due to be published in a volumeby Cambridge University Press, provides thefirst international synthesis of the extensiveinterdisciplinary research investigation on theVenice problem since the UNESCO Report of 1969.

Project teamDr Pierpaolo Campostrini – Director, CORILA Frances, Lady Clarke – President,Venice in Peril Jane Da Mosto – Researcher, CORILA Dr Caroline Fletcher – Venice Fellow,Department of Geography, University ofCambridge Prof Peter Guthrie – Centre for SustainableDevelopment, Department of Engineering,University of Cambridge Paul Richens – Vice Master, Churchill College Anna Somers Cocks – Chairman,Venice in Peril Prof Robin Spence – Director, CambridgeUniversity Centre for Risk in the BuiltEnvironmentDr Tom Spencer – Director, Cambridge CoastalResearch Unit, University of Cambridge

● Cambridge University CoastalResearch Unit

http://ccru.geog.cam.ac.uk/ CCRU carries out fundamental research oncoastal, estuarine and near-shore processes,landforms and ecosystems; environmentalmonitoring in the coastal zone, and researchconsultancies for both governmental and non-governmental agencies. It works in bothtemperate and tropical environments.The Unit’sbrief is to:● Provide scientifically-informed input for the

better management of shorelines and theirassociated ecosystems.

● Facilitate and promote multi-disciplinaryresearch into all aspects of shallow watermarine science by bringing together naturaland social scientists in Cambridge Universityand other governmental and non-governmental research institutions.

● Offer scientifically-informed advice on thesustainable management of coasts and coastalecosystems for coastal management and

and its students account for a significantproportion of the local population. It coversmany areas of chemistry and environmentalsciences; in the area of economics it carries outspecific environmental economics studies; in thearea of mathematics and IT it has developed andhas access to models and data managementinstruments; significant contributions are alsomade in the field of law.

■ Università IUAV di Venezia – IUAVVenice University

www.iuav.itFounded in 1926 it is an international referencepoint for architecture, history, design, andrestoration as well as for town and land useplanning. It also has laboratories forconstruction science and analysis of ancientmaterials.There are about 8,000 studentsenroled, 209 tenured professors and 240contract professors plus support and technicalpersonnel.

■ Università degli Studi di Padova –Padua University

www.unipd.itFounded in 1222, it was the first university inthe world to award a degree to a woman,Elena Lucrezia Cornaro Piscopia, in 1678 (inphilosophy). It has 13 faculties and 62departments and is a world leader in hydraulicengineering, biology, agricultural sciences,chemistry, mathematics and many otherbranches of science – not to mention centuries of tradition in law and medicine –matched by first-class facilities andinstrumentation.

■ UNESCO Office Venice – RegionalBureau for Science in Europe

www.unesco.orgFollowing the disastrous floods of 1966 inVenice and Florence and the ItalianGovernment’s invitation for UNESCO tocontribute, the Liaison Office for theSafeguarding of Venice was established in 1973on the occasion of the UNESCO InternationalCampaign for the Safeguarding of Venice. In1988 the UNESCO Scientific Co-operationBureau for Europe (SC/BSE) was relocatedfrom Paris to Venice and renamed as RegionalOffice for Science & Technology for Europe(ROSTE). In 2002, UNESCO established asingle office in Venice with the mandate toachieve UNESCO’s and Member States’ goals in the fields of science and culture.TheUNESCO Office Venice actively promotes,sponsors and convenes international scientificand cultural events in Europe and in theMediterranean region. A unifying theme forUNESCO is its contributing to peace andhuman development in an era of globalisation,through education, the sciences, culture & communication.

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OTHER ORGANISATIONS

■ Agenzia Regionale per la Prevenzionee Protezione Ambientale del Veneto(ARPAV) – Veneto Regional Agency forPrevention and EnvironmentalProtection

www.arpa.veneto.itThe Veneto Regional Agency for EnvironmentalProtection (ARPAV) is essentially the technicalbranch of the regional administration. Its taskscan be summarised as:* Environmental protection and monitoring;* Weather forecasting, monitoring and statisticalelaborations;* Organisation and management of the regionalinformation system for environmentalmonitoring and environment relatedepidemiology;* Environmental education and informationservices;* Technical and scientific services forenvironmental impact assessments andevaluation of environmental damage.

■ Agenzia per la protezionedell’ambiente e per i servizi tecnici(APAT) – National agency forenvironmental protection andtechnical services

www.apatvenezia.itThe Hydrographic Office has been operating inthe Lagoon since 1907 within Magistrato alleAcque but recently changed to be run fromcentral government. It manages a network of 52tide gauge stations for the systematicmeasurement of tide level and relatedparameters, such as wind direction and windspeed, atmospheric pressure, precipitation, andwave-height.

■ Consorzio per la gestione del Centrodi Coordinamento delle Attività diRicerca inerenti il Sistema Lagunare diVenezia (CORILA) – Consortium forCoordination of Research ActivitiesConcernine the Venice Lagoon System

www.corila.itCORILA is an association of Ca’FoscariUniversity and the University Institute ofArchitecture of Venice, the University of Paduaand Italy’s National Research Council. A non-profit organisation, it is overseen by the Ministryof Education, Universities and Research (MIUR).It was founded in 1999 to coordinate andmanage research on the Venice Lagoon andthereby provide decision support information topolicy makers and public administrations dealingwith Venice. Activities are organised within theframework of three-year research programmes,which in turn are divided into thematic areasand research lines.The principal thematic areasare: economics, architecture and cultural

heritage; environmental processes; datamanagement and dissemination.The firstresearch programme (2000–2003) costedapproximately €10,8 million of which nearly 60per cent was funded by the Special Law via theMinistry for Research. Co-financing was providedby other administrations as well as the researchdepartments and other partners themselves.

The second research programme(2004–2007) has just under €6m from theSpecial Law plus co-financing. Accordingly,CORILA facilitates the acquisition of knowledgeand information information on the physicalsystem, territorial, environmental, economic andsocial aspects of the lagoon and lagoonsettlements; processes and manages thisinformation in an integrated framework; carriesout interdisciplinary scientific research projectspertinent to the problems of the Venice lagoon;facilitates interaction with the internationalscientific community.The four partners ofCORILA have naturally been active participantsin research on the Venice lagoon system and thecity itself since the earliest times.

■ Centro Previsioni e Segnalazioni Maree– Tidal Forecasting and Early WarningCentre

www.comune.venezia.it/maree/ Founded in 1980, this organ within the VeniceMunicipality is responsible for the study andforecasting of storm surge events and alertingthe city in case of flood events. Observation ofsea level and meteorological parameters iscarried out through a monitoring network (11stations), that gives a real-time view of marineand weather conditions in the Venice lagoonand along the Adriatic coast. All stationsmeasure sea level and some also collectmeteorological parameters: air pressure,humidity, wind velocity and direction, waves andair temperature.

■ Consiglio Nazionale delle Ricerche(CNR) – National Research Council

www.cnr.itThe Italian National Research Council is a high profile public organisation in the field ofscientific and technological research. Founded in1923, it is composed of dozens of separateinstitutes, each with a particular specialisation. Inresponse to the increasing worldwide concernfor the survival of Venice, CNR established theInstitute for the Study of the Dynamics of LargeMasses in 1969, now incorporated within theMarine Sciences Institute (ISMAR). Created firstas a laboratory, it has spread from basic researchin oceanography and geology to appliedresearch.The other Venice-based branch ofCNR-ISMAR is the Institute for Marine Biology,established in 1946 as the National Centre ofTalassographic Studies, which focuses on pureand applied biological oceanography, marine andlagoon biology.

■ Consorzio per la Ricerca e laFormazione (COSES) – Consortiumfor Research and Training

www.provincia.venezia.it/coses/ COSES was established in 1967 by the municipaland provincial administrations to carry outanalyses, studies and projects to support publicsector activities – essentially via market research,data collection and statistical analyses concerningthe urban and regional economy, building sectorand housing, commercial distribution, tourism,culture, teaching and education, immigration,demographics, transport (especially water) andurban planning.

■ Insula SpAwww.insula.it Founded in 1997 by Venice Town Council (52percent share) together with Vesta (wastemanagement), Enel.Hydro (electricity), Italgas(gas) and Telecom Italia (telephones), Insula’smission concerns urban maintenance and, moreprecisely, measures such as clearing canals ofaccumulated silt, restoration of canal walls,foundations and façades of buildings lining canals,restoring bridges, rationalisation of urban subsoil(utility lines and sewer system), maintenance andrenovation of paving, raising of footpaths abovethe level of medium-high tides (local protection).Project integration and works coordination (allparties involved in the operations work side byside, not least the public utilities, who are Insula’spartners) is therefore essential to thiscomplicated process to minimise inconvenience,while also boosting the efficiency, in terms ofeconomies of scale in such a delicate urbanenvironment.

■ Istituto Veneto di Scienze Lettere edArti

www.istitutoveneto.itThe Istituto Veneto di Scienze, Lettere ed Artiwas founded by Napoleon Bonaparte “to collectdiscoveries, and to perfect the arts and sciences”.Its current mission is to increase, promulgate andsafeguard the sciences, literature and arts,bringing together outstanding figures from theworld of scholarship.The Institute also supportsspecial research projects that concern Venice andthe Veneto, and which are addressed at theinternational community.Together with variousuniversities and the National Research Council, ithas also set up specialised centres for researchinto environmental questions, into philologicaland literary aspects of the language of theVeneto, and into Hydrology, Meteorology andClimatology. It runs a programme to integrateand share environmental data among all themajor institutions and research bodies.

■ Università Ca’ Foscari di Venezia www.unive.itWith four faculties and 19 departments, theUniversity dates back to the late 19th century

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Jetty A protective structure of stone or concrete extending into the sea toinfluence the current or tide, in order toprotect harbours, shores and banks. (1) On open seacoasts, a structure extendinginto a body of water to direct and confinethe tidal flow to a selected channel, or to prevent shoaling. Jetties are built at the entrance to a bay to help deepen and stabilise a channel and facilitatenavigation.

Lagoon (coastal/tidal) A shallow area ofwater separated from the sea by a sandbankor by a strip of low land, and usuallyconnected to the sea by one or more inlets.It is considered to be an open, complex anddynamic system – open in terms of theexchanges with the sea and watershed;complex and dynamic because of the largevariations in physical, chemical, ecological andphysiological characteristics within it and overtime. Exchanges in material and energy arestrong across the land/water, air/water andwater/sediment interfaces.

Mathematical modelling Computers allow scientists to construct increasinglydetailed ‘models’ of how a system behavesand to ask questions about it.Theireffectiveness depends on the prevailing level of understanding of the real world –the main features of the system and thefactors influencing it. Models are used toexplain past changes, to investigate whyobserved changes are happening and topredict impacts of planned interventions.Physical processes can be modelled fairlywell, but it gets more difficult once biologicalfactors are added. Computer models alsodepend on accurate data for calibration,validation and prediction. Improvedenvironmental monitoring, instrumentation,computing powers and communicationstechnologies are helping to make modelseven closer to real systems.

Morphology The scientific study of the forms of things. In biology, the physical form and structure of animals and plants.In geology, the structure, form, andarrangement of rocks and landforms.In the case of a lagoon, its physical form is the result of hydrodynamics (the waywater moves and is exchanged) and the influence of plant and animalcommunities.

Moto ondoso Wave action, which is a keycause of erosion in the lagoon and city.In the lagoon, waves are primarily generatedby winds whereas the propeller action ofmotor boats creates the most destructivewave action within the inner canals.

Mudflat A flat area in the lagoon, covered witha thick layer of mud or sand. Mudflats areusually exposed at low tide but covered athigh tide.They may grade into saltmarsh ifconditions allow sediment to build up andbecome stabilised by plants, and the twosystems interlink.

Murazzi Sea walls of stone, concrete, or othersturdy material, built along the shoreline toprevent erosion and other damage by waveaction.The lagoon’s murazzi were first built inthe 18th century and constitute the first lineof flood defence. Parts of the murazzi werebroken during the 1966 flood.

Nutrients Elements or compounds essentialfor animal and plant growth. Major plantnutrients are phosphorus and nitrogen. Inexcess concentrations they can causeimbalances and eutrophication (q.v.).

Saltmarsh A coastal wetland ecosystem that isperiodically inundated by seawater. Plants inthis community have special adaptations tosurvive in salty conditions that would killmost land plants. Saltmarshes support vitalphysical and biological processes that governthe health of the lagoon.Venice’s saltmarshes,locally known as barene, offer a uniqueenvironment within the Mediterraneanthanks to the marked tidal cycle and thestabilisation of certain dynamics by humanintervention over ten centuries.

Seagrass Aquatic plants with a developed rootsystem anchored underwater in shallowbeds. Seagrass beds are important lagoonhabitats, especially for young fish, and help tostabilise the lagoon bed.

Sediment There are various classes ofsediment, from fine mud and silt to coarsersand, suspended in or settled out of water. Ina lagoon, sediment is continually shifting, tobe deposited in other areas within thelagoon or out at sea.

Seiches Seiches are periodic oscillations ofwater in a closed basin that follow a stormsurge, rather as bath water continues to riseand fall for a while after you set the water inmotion. One or more seiches following astorm surge may cause repeated flooding orexpand the duration of a flood episode.

Sirocco A hot, dry, dust-laden wind that blowsfrom the Sahara Desert north or northwestacross North Africa. It picks up somemoisture as it travels over theMediterranean. It is associated with storms inthe Mediterranean Sea, and cold, wetweather in Europe.The Sirocco’s durationmay be a half day or many days.

Global warming An increase in the averagenear-surface temperature of the Earth. Globalwarming has occurred in the distant past asthe result of natural influences, but the term ismost often used to refer to the warmingpredicted to occur as a result of increasedemissions of greenhouse gases (carbondioxide, methane, nitrous oxide and othergases released into the atmosphere by theburning of fossil fuels.) Thought to beresponsible for changes in global climatepatterns. Scientists generally agree that theEarth’s surface has warmed by about 1°F in the past 140 years.

Greenhouse effect A popular term used todescribe the roles of water vapour, carbondioxide, and other trace gases in keeping theEarth’s surface warmer than it would beotherwise.These gases trap solar radiation, asthey allow incoming sunlight to pass throughbut absorb heat radiated back from theEarth’s surface. Many human activities causelevels of these gases to rise, resulting in anincrease in the Earth’s temperature.

Groundwater This is water held within theinterconnected openings of saturated rock(usually in aquifers, q.v.) beneath the landsurface, that can be used to supply wells andsprings.The long filtration route means thegroundwater is relatively clean; howevercontamination can reach groundwaterreserves and is generally expensive anddifficult to clean up.

Hydrodynamics The study of fluids in motionand the movement of objects through fluid. Inrelation to the subject of this book, howwater moves in the lagoon, and the effect ofnatural and built structures on its flow – fromthe winding tidal creeks to the breakwaters atcoastal inlets.

Habitat The place where a plant or animalspecies naturally lives and grows, finding thenutrients, water, shelter, living space, and otheressentials it needs to survive. Habitat loss,which includes the destruction, degradation,and fragmentation of habitats, is the primarycause of biodiversity loss.

Insulae These are the islets within the historicalcentre of Venice and the term is now used torefer to a local flood defence strategy whichinvolves raising the perimeter of individualislets and waterproofing measures, pumpingsystems and valves on the interior. Small-scalemovable barriers may also be installed at theentrances of the inner canals connected tothe individual islet.This approach has beenimplemented at Malamocco (Lido) and isunderway for the San Marco islet and theisland of Burano.

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decision-making within governmental andnon-governmental institutions andorganisations in the UK and overseas.

● Churchill College, University ofCambridge

www.chu.cam.ac.ukThe college was endowed by some of theworld’s most famous companies, charitablefoundations and benefactors, which enabled SirWinston Churchill to launch his remarkableeducational venture – Churchill College.Thecollege was created as an internationalmultidisciplinary community for the study of thesciences and the humanities in order to meetthe national need for scientists andtechnologists, and to forge links with industry. Itis one of 31 colleges of the University ofCambridge, and is set in 40-acre grounds. As thefirst major work of modern architecture in theUniversity, it has been judged “an outstandingconception”, “the best of the new”.

GLOSSARY

Acqua alta Literally ‘high water’ in Italian, theterm is used to describe periodic flooding inVenice city and islands, usually during thewinter months. It has been a feature of Venicefor centuries but incidents of high water arebecoming increasingly common as averagerelative water level rises.

Algal bloom Sudden, massive growths ofmicroscopic and macroscopic plant life, algaeand cyanobacteria, which develop in lakes,reservoirs and marine waters. Algal bloom isusually the result of urban and agriculturalrunoff from the watershed area and mayresult in the death of other aquatic life,including fish and seagrasses. It was the mainwater quality issue for Venice in the 1980s-90s. (See ‘eutrophication’)

Aquifer A geological formation or structure thatstores water, like a giant underground sponge.The water-bearing rocks that composeaquifers consist either of unconsolidated (soil-like) deposits or consolidated rocks.Waterflowing into recharge areas - land coveredwith soil and trees – refills the aquifer;wetlands absorb and store water that laterslowly drains into aquifers.To tap thegroundwater (qv) in an aquifer, wells are duguntil they reach the top layer of the aquifer,the water table.When a lot of water ispumped from an aquifer, or when there is adry spell, the water table sinks lower andcauses land subsidence (q.v.).

Bora Named after Boreas, God of the NorthWinds, a strong, cold and dry north-easterlywind that blows from the Alps across theAdriatic. It can be very dangerous in thelagoon, provoking high waves. Bora winds aremost common during the cool season(November through March).

Breakwater A protective structure of stone or concrete; usually protecting a harbour or beach, designed to break the force of thewaves and so prevent a beach from washingaway or mitigate the exchange of waterbetween the Adriatic and the lagoon.Breakwaters are typically built parallel to the coast.

Biodiversity A contraction of ‘biologicaldiversity’, to describe the number, variety andvariability of living organisms. Biodiversity iscommonly defined in terms of the variabilityof genes, species and ecosystems,corresponding to these three fundamentaland related levels of biological organization. Itis significant as regards individual habitat typesand for the whole lagoon region.

Drainage basin The tract of land that feeds agiven body of water (lake, lagoon, etc) withwater originating as precipitation (snow, rain).The water may drain through the ground orbe carried in rivers and streams. Other termsinclude ‘catchment area’ and ‘watershed’.

Ecosystem A basic functional unit in ecology:all the organisms in a particular area, and thenon-living environment that supports them.All components are considered inseparableand depend on each other, either directly orindirectly. Ecosystems are dynamic: theirboundaries and constituent parts change over time.

Endocrine disruptors These are syntheticchemicals that when absorbed into the bodyeither mimic or block hormones, whichdisrupt the body’s normal functions. Manychemicals, particularly pesticides andplasticisers, are suspected endocrinedisruptors.They are typically persistent in theenvironment and they accumulate in fat.

Erosion The wearing away of land, soil or builtstructure by the action of wind or water orboth (waves). In the lagoon, erosion mainlyoccurs along the edges of the saltmarshes andbetween the shallows and the inner channels,so that sediment is carried out to sea by thecurrent or it deposits in the channels whichthen have to be mechanically dredged.

Eustacy (eustasy) Changes in sea level on aglobal scale due to expansion ocean volumeand/or factors relating to global warming.Usually refers to worldwide change – anincrease or decrease in sea level due to moreprecipitation returning to the ocean (whichindicates glacial ablation or inter-glaciation).Changes in sea level can result frommovement of tectonic plates altering thevolume of ocean basins, or when changes inclimate affect the volume of water stored inglaciers and polar icecaps. Eustacy affectspositions of shorelines.

Eutrophication The process by which excessnutrients (q.v.) entering a body of water leadsto the excessive growth of particular aquaticplants, at the expense of other species.Thewater becomes starved of oxygen, producingan environment that does not readily supportaquatic life.The most serious problems ofeutrophication result from the massive growthof single-celled algae (see algal bloom).

Gabion Steel wire-mesh basket to hold stonesor crushed rock, to protect a bank or bottomfrom erosion. Now used in saltmarshrestoration experiments in the lagoon, wheregabions of more biodegradable materials arealso being trialled.

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INDEXFor definitions, see Glossary.For information on key organisationsand legal framework, see Appendix.

Acqua alta 31, 40, 52, 64Adriatic Sea: 27, 42, 52, 58, 76

history of 18, 64storms in 32, 64winds affecting 32

Agricultural pollution 2, 28Algal bloom 28, 70Aquifer 35Architectural surveys 34, 43, 47

Barrier (see Ch 5 esp.)construction of 62–3debates about 10, 46, 70ffdecision to build 9–10, 64ecological impact of 66, 68, 70future and 11, 78lessons from other schemes 66-9MOSE 64–5, 70need for 46, 59, 71operation of 62, 64–5, 70purpose of 61, 70

Basilica of St Mark’s 34, 43, 46, 37Bora wind 32Breakwaters 60, 65, 71

Canals, repair and renewal 48–9Canaletto 36Caranto 34Chioggia inlet 58, 63, 65Clam fishing 25Climate change 26, 76ffCoastal defences 46, 58–9Comitatone 46, 64Computer modelling 25, 59, 76–7Consorzio Venezia Nuova (CVN)

46–7, 64CORILA 10Creeks (tidal) 24, 27, 55–7

Drainage basin 27Dredging:

of canals 46, 48–9of navigation channels 24, 55 and new islands 54

‘Diffuse’ measures 46, 52ff, 71

Ecosystem of lagoon 28Ecological impacts 28–9

of barrier 70Erosion:

coastal 58, 72in lagoon 24–5, 28–9, 55, 71impact of 26, 29

Eustasy 36Eutrophication 28

Fish farms 22, 55Flooding (see Ch 3 esp)

extreme events 33, 40reasons for 32ffimpact of 36ffincrease in frequency 40–411966 flood 32–3, 36, 46, 48, 71

Flood control:barrier and coast 10, 58ff, 72‘diffuse’ measures 46, 52ff, 72‘local’ measures 46–51, 72natural 26, 52radical proposals 71, 78–9

Floodgates 62–3Flushing, of lagoon 64, 70

Gabion 54Global warming 76Groundwater extraction 35

Habitats of lagoon: 19–21, 54damage to 26–8, 54restoration of 52ff, 72

Hydrodynamics of lagoon 23–26,40, 58channels and 26, 40

Industry 23, 81Industrial pollution 27–9, 81Inlets

changes to 24, 52, 58, 65construction of 22–3sediment loss from 25

IUAV survey 47Insula SpA 46, 48Insulae 20, 46Istrian stone 35, 40, 49

Jetties:construction of 22impact of 24–5modifications to 58

Lagoon: (see Chs 2 and 4 esp)becoming marine 24–5, 71, 79biodiversity of 19-21, 80ecological decline of 11, 25–8, 54ecological importance of 18–19,54, 80habitats 19–21, 54history of 18, 22ff, 54hydrodynamics (water flow)23–5, 26, 40, 58impact of barrier 64, 70–1importance to Venice 22, 32, 52key changes to 22–3, 72, 76‘natural laboratory’ 78–9physical degradation of 24, 26, 29,54–5physical structure 20–1, 26, 40 pollution of 26–9restoration of 46, 54ffsediments in 23–4, 54sediment loss 24–5, 55semi-natural system 18, 22, 72,77ff, 80

shrinking in area 22, 26, 40, 55surveys of 23–4

Lido inlet 58, 62–3, 65‘Local’ flood defences 45–51

Mediterranean, and climate change76–7Migrating birds 69Marghera 23, 27–8, 35, 55, 81Malamocco inlet 25, 58, 62–3, 65Mathematical modelling 25MOSE 64–5, 70Mobile barrier – see ‘barrier’Moto ondoso – see ‘waves’Mudflats 23–4, 26, 54Murazzi – see ‘sea walls’

Navigational channels:construction of 23impact of 24, 52, 55modifications to 55

Nutrients, excess 28

Pollution: 27, 54, 69–70, 79sources of 26, 28impact of 28–9, 48

Punta della Salute 33

RAMSAR 17Rivers, diversion of 22–3, 24, 26Rotterdam and E. Scheldt barrier

66, 68

St Mark’s Square 37, 43, 47, 50–51St Petersburg flood barrier 66, 69Salt damage 40, 48–49Saltmarsh:

as habitat 26importance of 26, 52loss of 23–4, 26, 71restoration of 54ff

Seagrass 25, 28Sea level:

and climate change 26, 36, 59, 76measuring 33–4, 76reference level 33rise, causes of 33, 36, 40

Sea walls 20–1, 22–3, 46, 58Sediment 24, 28, 55, 58, 71

budget 24–5fence 54loss 24, 55, 71

Seiches 33, 68Sewage 46, 79

pollution from 27–8repairs and renewal 46

Shipping 23, 62–3, 65Sirocco wind 32Special Laws 9, 10, 48, 64Storm surges

causes of 32difficulty in predicting 40, 76in 1966 33, 71

Subsidence 34–5, 77

Thames Barrier 66–7Tides: 19, 25, 29

1966 flood 33, 36, 46, 48, 71extreme high tides 33, 36, 41seasonal pattern 32, 70and storm surges 32–3, 71and sediment loss 25

Tidal creek – see ‘creek’Tourism 11, 81–2

UNESCO 11, 81

Veniceauthorities governing 46, 80 (see also Appendix)diversion of rivers 22–3, 24, 26flooding in 32ff, 40, 55, 59history of 9, 17–8, 22–3, 35, 47importance of lagoon 24, 32need for barrier 59, 64, 71local defences 46–51population 42, 80problems facing 9–11, 32, 36, 40,42ff, 59, 80–1restoration and renewal 45–51sea level rise 10, 34, 36, 42, 58–9sewage in 27, 48–9sinking of 32, 34–5Special Laws 9, 48, 64sustainability of 11, 80–1what future for? 10–11, 58, 71,76–7, 80ffWorld Heritage Site 11, 17,47, 81

Venice Water Authority 46Venice Town Council 47, 48Venice in Peril 9, 10

Waves (moto ondoso)erosion by 26, 28–9damage to buildings 42

Weather prediction and barrieroperation 62, 64–5, 77and climate change 76–7difficulties of 36, 65, 76–7

Water flow – see ‘hydrodynamics’Water quality 22

decline in 27–8barrier and 70

Water treatment 27, 47, 55Wetland 10, 18–19, 81

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Storm surge A rise in sea level caused bywind and pressure systems; its typical effect isto raise the level of the tide above thepredicted (astronomical) level.The magnitudeof the storm surge is dependent on theseverity and duration of the event and theseabed topography at the site. Storm surgesare potentially catastrophic, especially in deltaic regions with onshore winds at the time of high water level and extreme windwave heights.

Subsidence Decrease in the elevation of landsurface due to tectonic, seismic, or artificialforces – such as the loss of undergroundwater support. It is also brought about by landuse changes that may directly compact theground (e.g. heavy buildings) or accelerateoxidation rate of the organic content of soils.

Sustainability The concept of meeting theneeds of the present without compromisinglong-term balance and availability of resources.In nature conservation terms, it refers to theuse of a natural resource in a way where itcan be renewed, thus maintaining theenvironment’s natural qualities.Today, it appliesto many disciplines, including economicdevelopment, environment, food production,energy and lifestyle.

Tidal creek A small tidal channel through acoastal marsh, draining into open water andsometimes forming an internal pan within thesaltmarsh.

Tides (and how they work) The periodic riseand fall of sea level under the gravitational pullof the moon on the Earth’s waters.The sunalso exerts a pull, but less than half that of themoon. Especially high tides (‘spring tides’)occur when the sun and moon are lined upwith the Earth at new and full phases of themoon. Conversely, when the sun and moonare on opposite sides of the Earth, theyinterfere with each other and tides aregenerally weaker; these are called neap tides.Tides occur regularly, twice every day.

Watershed See drainage basin.

Wetland An area that is regularly saturated bysurface water or groundwater and ischaracterised by vegetation adapted for life insaturated soil conditions (e.g. swamps, bogs,fens, marshes and estuaries); a transitionalzone between dry land and aquatic areas,staying wet at least part of the year becausethe water table is at the surface.

PICTURE CREDITSAlberto Tomasin (Dip. Matematica Applicata,Università Ca’ Foscari di Venezia/CNR-ISMAR):33, 34, 78Archivio di Stato: Endpaper, 22 (Savi ed esecutorialle acque, serie Laguna, dis. 13), 64 (Savi edesecutori alle acque b. 123, dis. 6)Autorità Portuale di Venezia: 55Frédéric Brochier: 79, 81Dario Camuffo (CNR-ISAC): 36 (with kindpermission of Kunsthistorisches Museum Vienna), 41 Centro Segnalazioni e Previsioni Maree –Comune di Venezia(CSPM): 32, 33, 41Frances, Lady Clarke: 76Consorzio Venezia Nuova/Magistrato alle Acque– Servizi Informativi: 12, 16–17, 18, 22-23, 37,64, 65Consorzio Venezia Nuova/Magistrato alle Acque– Archivio Fotografico: 77CORILA/Enrico Rinaldi: 11, 27, 29, 59Luigi D’Alpaos (Dip. IMAGE, Università diPadova): 24, 25Environment Agency/ David Wilkes: 67Caroline Fletcher: 26, 42, 49Gazzettino: cover, 13, 23, 43, 58–9, 60-61, 81Gianni Berengo Gardin: 8-9Insula Spa: 13, 40, 44–5, 46, 47, 48, 49Morzaschita (St Petersburg, Russia): 69Museo Correr: 35 (G. Grevembroch (fondadori v.III.149))Michele Pellizzato (Biologa ed esperto dellapesca,Venezia): 18-19, 25, 54-55, 59Sarah Quill: frontispiece, 10–11, 12, 13–14, 15,28-9, 30–1, 36, 37, 38-9, 43, 49, 52–3, 70-1, 73,74-5, 77, 81, 82–3Rotterdam Department of Water Management/R. Bol: 68

Illustrations: Robbie PolleyGraphs: Clive Goodyer

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