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Part I · Introduction

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Cambridge University Press0521840465 - Flooding and Environmental Challenges for Venice and its Lagoon: State of KnowledgeEdited by C. A. Fletcher and T. SpencerExcerptMore information

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INTRODUCTION

‘There really is no point in continuing to rescue andrestore individual buildings in Venice if the cityremains under increasing threat from flooding. Nowwhat can be done about that wider issue?’ With thesewords in late 2000, over lunch in the Master’s Lodgeat Churchill College, Cambridge, Anna SomersCocks, the Chairman of Venice in Peril (The BritishCommittee for the Preservation of Venice) set in traina broad series of research activities in Cambridge andVenice. One of several substantive outcomes of thatprocess is this volume.

HOW IS VENICE TO BE SAVED?

It is now nearly forty years since the disastrous stormsurge of 3–4 November 1966 which flooded manyparts of Venice to water depths of nearly 2 m abovemean sea level. As Howard Moore notes in the pref-ace to this book, that event was the catalyst for aninternational gathering of scientists to discuss the‘Venice problem’ in 1969. Since that time a great vol-ume of detailed research has been undertaken inVenice, elsewhere in Italy and around the world, onthe geology, hydrology, ecology and biogeochemistryof the Venetian built environment and the VeniceLagoon, and the linkages of these habitats to theAdriatic Sea and the hinterland of the Veneto. Therehave been considerable technical developments,including, for example, the monitoring and mathe-matical modelling of tidal inlet and lagoon hydrody-namics. New problems have emerged, covering suchdiverse issues as the anoxic crises and algal blooms ofthe 1980s, the ecological and morphological impactsof hydraulic dredging for clams since the 1990s, andthe recent identification in the lagoon of a range of

chemicals which affect biological systems at very lowconcentrations (the endocrine disrupters). Further-more, there has been a growing realization of the spa-tial and temporal scale of sampling needed toeffectively define the complex dynamics of bothlagoon and watershed. Most recently, these issueshave come to be seen against the backdrop, anduncertainties, provided by what global environmen-tal change might mean for Venice. All these develop-ments, amongst many others, are covered in detailin the chapters of this volume. However, the over-arching problem of rising water levels and associatedserious city flooding and what to do about it stillremains the most apparent key issue facing Venice.And there are many indications that the problem isworsening. Whilst the 1966 event has not beenrepeated, of the ten highest floods between 1900 and2004, 8 occurred after 1960. In the first decade of thetwentieth century the lowest part of the city, StMark’s Square, flooded ten times per year or less. Bythe 1980s, flooding was occurring 40 times per year.In the winter of 2002, there were 10 ‘exceptional’floods (when nearly 4 per cent or more of the city isinundated) in one period of three weeks.

Within this context, this broad review of the ‘stateof knowledge’ comes at a particularly timely pointin the long history of flood protection measures forthe city. The 1966 event concentrated minds. In 1971 a‘competition of ideas’ was held and won by a designfor an underwater mobile barrier to close off the threelagoon inlets at times of storm surge. A deciding fac-tor was the importance of aesthetics; the barrierwould lie on the seabed and only be raised, and thusvisible, at times of high water. In 1984 the SpecialLaw for Venice (see Appendix A2, this volume) cre-ated the Consorzio Venezia Nuova (CVN), a consor-tium of large Italian engineering and construction

Scientific paper

1 · Venice and the Venice Lagoon: creating a forum for international debate

T. SPENCER, J. DA MOSTO, C. A. FLETCHER AND P. CAMPOSTRINI

Flooding and Environmental Challenges for Venice and its Lagoon: State of Knowledge, ed. C. A. Fletcher and T. Spencer.Published by Cambridge University Press, © Cambridge University Press 2005.






companies, which was given sole responsibility forimplementing the barrier solution, within a moregeneral remit from the Ministry for Public Works forthe planning, design and execution of all publicworks for the safeguarding of the lagoon. As part of apackage of ‘hard’ and ‘soft’ engineering measures(now referred to singly as the ‘MOSE system’), qual-ified approval for implementation of the mobile bar-rier system, and associated navigation locks,breakwaters and inlet modifications, was finallygiven in April 2003, at the halfway point of the Venicein Peril initiative that underpins this volume. Thesedecisions have had a reinvigorating effect, bothsharpening up some long-debated issues (the wholequestion of water, sediment and nutrient exchangesbetween the Adriatic Sea and the lagoon for instance)and generating some quite new questions (might thegates be used to control water circulation and thuswater quality in the lagoon?) to which we have yetto apply existing knowledge or devise new, criticaltests. Furthermore, one of the key questions concern-ing barrier impact, that of the frequency and durationof gate closures, and its seasonal variation, is cru-cially related to near-future changes in sea level andstorminess consequent upon greenhouse-gas relatedenvironmental change.

WIDENING THE REMIT

The long delay between the original concept, comple-tion of testing of the prototype mobile barrier in 1992and the final decision to implement the ‘MOSE’storm protection system reflects the intensity of sci-entific, social and political debate over whatapproach is best for Venice and its lagoon. Apartfrom the issue of cost (currently budgeted at €4bn or£2.7bn) and whether this expenditure should be apriority, serious and sustained challenges to thisscheme have come from the engineering arena, whenconsidering the risks associated with such an innova-tive barrier system and irreversibility of the structure,especially in the light of adaptations to the possibleeffects of climate change. Ecological concerns havealso been repeatedly highlighted – when the flood-gates are closed, the lagoon will become cut off fromthe benefits of tidal flooding. This has implicationsfor both sediment exchange and water quality, the

former with consequences for the maintenance oflagoonal saltmarsh accretion in the face of sea levelrise and the latter raising the spectre of a return to thealgal blooms seen in the lagoon in the 1980s.

Over time numerous debates over the merits anddemerits of a mobile barrier scheme have becomehighly polarized, resulting in oversimplification ofthe key issues governing the ‘health’ of the lagoonand safety of the city, notably lagoon ecosystem char-acterization, functional dynamics and evolutionarytrends and the relations between the lagoon, the cityand the large watershed of the Veneto that feeds intothe lagoon. Tackling this level of questions requiresa more sympathetic and more holistic view of Veniceand its lagoon and a willingness to listen to, anddraw information from, a wide range of specialist sci-entific disciplines into a more thorough synthesis.

CREATING AN INTERNATIONAL FORUM:PROCESS AND PRODUCT

With generous financial backing from Venice in Periland its supporters in place, a research plan was for-mulated in 2001 by a group of scientists, engineers,architects and geographers, largely drawn fromCambridge University’s Centre for SustainableEngineering, Centre for Risk in the Built Environmentand the Cambridge Coastal Research Unit, and devel-oped in association with CORILA, the Venetian con-sortium for the coordination of research activitiesconcerning Venice and the lagoon system. Within thebroad aim of promoting the objective study andreview of information concerning the ‘Venice prob-lem’, it was agreed to develop a three-stranded collab-orative research programme. This consisted of aninformation gathering process; the promulgation of aseries of workshops; and the organization of an inter-national discussion meeting.

By September 2002, the project was in a positionto mount the scientific and technical workshops in anumber of Cambridge Colleges. The workshops, eachattended by 12-15 participants, covered the follow-ing five themes: urban flooding – architectural andstructural issues; engineering solutions to storm surgeflooding of Venice; physical and ecological processesof the Venice Lagoon; modelling the hydrodynamics,morphology and water quality of the Venice Lagoon;

4 T. Spencer et al.






and global environmental change, uncertainty, riskand sea-level rise in the North Adriatic Sea. The aimof the workshops was to identify and outline the keyflooding and environmental issues; identify researchrequirements (in both the mid- and long-term); high-light areas of information need where current under-standing of the complex Venice system requiresfurther elaboration; raise matters concerning commu-nication of science and data availability; and, notleast, in a relatively informal setting with no formalrecording of proceedings, allow the exploration of lessmainstream and more innovative solutions toVenice’s environmental issues. Participants at eachworkshop were a mixture of researchers workingspecifically in Venice and internationally recognisedexperts on the issues under consideration.

A prime aim of the workshops was to act as asounding board and pump-priming operation forplanning of the international discussion meeting tobe held in Cambridge 12 months afterwards. Thismeeting duly took place in Churchill College,Cambridge in September 2003, under the title‘Flooding and Environmental Challenges for Veniceand its Lagoon: State of Knowledge’. The papersgiven at that meeting, attended by 130 scientists andengineers from Italy, the UK, The Netherlands,Denmark, Germany, Spain, Lithuania, Russia and theUSA, subsequently developed and revised, and withadditional invited contributions and commentaries,are presented here. The aim of the collection is toshow what is currently known about the city andlagoon; where debate remains; and where criticalinformation and tests of key hypotheses are still lack-ing. The text reports the wide spectrum of scientificarchival, field, laboratory and modelling studies onVenice and its lagoon; shows the considerable intel-lectual challenges involved in trying to understandthe workings of a complex, highly managed andaltered, and highly stressed set of ecological habitats(in the widest sense, from buildings to plants, bothpredominantly rooted in salty water); and identifiesthe need to overcome past shortcomings in researchco-ordination and effective dissemination of researchresults in order to deliver key understandings of cityand lagoon dynamics to opinion makers and decisiontakers.

ACKNOWLEDGEMENTS

This project is a contribution to the CambridgeEnvironmental Initiative of Cambridge University(formerly the Cambridge Committee for Inter-disciplinary Environmental Studies). We are gratefulto Peter Guthrie, Paul Richens and Robin Spence fortheir participation in the Project team, along withFrances Clarke and Anna Somers Cocks, distin-guished by their vision and tenacity, and to Sir JohnBoyd and Janet Milne of Churchill College, whohosted and helped with the organization of theInternational Meeting. Venice in Peril, the SaveVenice Boston Chapter, the UNESCO Office in Venice– Regional Bureau for Science in Europe (ROSTE)and the Regione Veneto provided material supportfor the Meeting. And above all, we recognize themany scientists who have applied, and continue toapply, their talents and energies to improving ourunderstanding of this most remarkable of ecosystemsand home to a unique cultural heritage.

Venice and the Venice Lagoon 5






Venice built her fortunes on the sea: a huge emporiumof trade between the Orient and the West. A connect-ing point between the Middle East, the Mediterraneancoasts and continental Europe, that reached the peakof its political and commercial power, between thefifteenth and sixteenth centuries, thanks to the controlof maritime routes. But – this is the first question –was Venice (and is Venice) a city on the sea?

In fact Venice is not – as one would normally think– a maritime city provided with docks or waterfrontsfacing the sea, like Marseille, Genoa, Naples, Istanbulor most of the other major and minor sea ports on theMediterranean and Atlantic coasts. Venice is in factan island (or rather a series of islands, a crowded‘archipelago’), well inside a protected lagoon, capi-tal of an independent Republic until 1797: the mainisland, amongst the dozens scattered all around thelagoon, the heart of a complex productive and resi-dential environment densely populated until a fewdecades ago.

Today many parts of the lagoon are wastelandsfull of abandoned settlements formerly used for cen-turies, and even in the recent past, by fishermen,sailors, boatmen and people living on local agricul-ture and trade. More or less as in the twelfth century,when the ancient Rialto archipelago became defini-tively the capital of the Commune Venetiarum, cradleof the new-born Republic which developed as aninternational power after the Fourth Crusade, butwas still located in a narrow marshy area spreadingalong the Adriatic coasts, compressed between theAdige and Isonzo river mouths.

Even today Venice and its lagoon should be seenas a single entity (as it used to be) and the ancientcapital as the centre of a wider productive, commer-cial and residential system, in which water can becompared to the green belt commonly found in other

major metropolitan areas. Not a liquid desert, but anessential part of a ‘diffuse city’, with the canals actingas boulevards and the lagoons as ‘fields’, to be fre-quented like Hyde Park in London or Central Park inNew York. But the vast, shallow and placid watersurface of the lagoon is today considered more as anobstacle, that can be criss-crossed by fast, and oftenhuge, destructive motorboats racing from land to seaand back. Or maybe bypassed with rapid under-ground connections, as some local planners propose.

On the other hand, the lagoon is often simplyconsidered as the natural ‘frame’ and backgroundfor the former amphibian ‘Queen of the Sea’, anecosystem to be preserved – together with the stonesof Venice – for its beauty and uniqueness. An ecosys-tem that should still be considered (as it was) a life-giving territory for the survival of the diffused cityas a living organism and as a capital of Europeanculture populated not only by hurried masses ofday-trippers.

Comparisons between the present and the situa-tion of the lagoon centuries ago is probably impossi-ble, but Venetians were not interested in such‘aesthetic’ questions concerning the lagoon wherethey lived: their primary, if not their only, concern,as we shall see, was with strategic security, maritimenavigation and sanitary matters. The lagoon wasmodified over the centuries as the permanent site fora once Mediterranean-wide civilization. Individualneeds were not allowed to prevail and always hadto be subordinated to the general interest: full privateproperty of water surfaces was not admitted and ourforefathers managed to guarantee a precarious butlasting balance between land and sea, adapting andsomehow taming an unstable environment, threat-ened both by freshwater floods and by sea-sand andriver-silt deposits.

Scientific paper

2 · Between salt and fresh waters

G. CANIATO

Flooding and Environmental Challenges for Venice and its Lagoon: State of Knowledge, ed. C. A. Fletcher and T. Spencer.Published by Cambridge University Press, © Cambridge University Press 2005.






Venetians knew perfectly well – if they wanted tosurvive as an independent Nation – that they had topreserve a permanent balance between land andwater: they understood that a coastal lagoon – lefton its own – will naturally be transformed into opensea (if tides and currents prevail) or into land (if sed-iments brought by rivers prevail). Thus, water man-agement slowly changed the first marshy locationinto an ‘artificial’ (or rather, ‘anthropic-shaped’) envi-ronment, permanently suitable for the safe settlementof a human community in constant expansion.

In fact, winding your way through the canals ofthe lagoon – far from the centre of Venice and beyondthe major islands of Burano and Torcello – you willfind yourself immersed in a flat landscape that can befully understood only from the air, with little scat-tered islands emerging just a few inches above water

level. A peculiar environment that – especially at lowtide – often becomes a muddy plain: the only protec-tion for the only capital in the world that never hadwalls. And truly the vast, shallow lagoon surfaceswere – as our forefathers knew – the walls of Venicethat enemy armies could not scale or destroy. A sortof dogma, recalled by the Renaissance humanistGiovan Battista Cipelli, better known as Egnatius:

Venetorum urbs divina disponente providentiaaquis fundata, aquarum ambitu circumsepta,aquis pro muro munitur. Quisquid igitur,quoque modo, detrimentum publicis aquisinferre ausus fuerit, ut hostis patriae iudicetur,nec minori plectatur poena quam qui sanctosmuros patriae violasset. Huius edicti ius ratumperpetuumque esto.

8 G. Caniato

Fig. 2.1 Traditional fishing in the shallow waters of the lagoon near Sant’Erasmo sea port (photograph by Catullo andLagomarsino: Venice, 1990).






The city of Venice, founded by divine provi-dence on the waters, is surrounded by waterand has water for its walls. Therefore, if any-one in any way should damage these waters,he shall be judged an enemy of the state andshall receive no less punishment than if he hadviolated the holy walls of the homeland. Thisruling is given in perpetuity.

A muddy landscape, criss-crossed by a network ofmajor channels and minor tortuous canals ramifyingfrom the sea ports to the river deltas of the mainland.The ‘veins and arteries of a living organism’ as ourforefathers used to say, the lagoon being the naturalextension and indispensable support of the mainisland: Venice, fulcrum of a vast ‘diffuse city’ whosewaterways were carefully maintained and used daily,giving vitality to the minor islands that providedimportant support for fishing (Fig. 2.1), transport,

trade, agriculture and all those activities that used tomake the lagoon a lively and populous environment.

The end of the Venetian Republic (and the wide-spread use of the islands for ‘military’ purposes dur-ing the following twenty or so years of recurrentwarfare) marked the end of this ancient and well bal-anced interconnection between Venice and its liquidsurroundings. A powerful ‘protective belt’ with mas-sive fortifications – of which Venetians had never feltthe need – was built well inside the lagoon and on theedge of the nearby mainland; insular convents andmonasteries were abandoned or destroyed and thenearby canals gradually started to lose their impor-tance (Figs. 2.2., 2.3). In more recent times peoplebegan to reach Venice across the railway bridge (builtin 1846), followed in 1933 by a parallel road bridge,with adverse affects on the old waterways that usedto serve the city linking it both to the mainland andthe sea ports.

Between salt and fresh waters 9

Fig. 2.2 Late eighteenth-century engraving of the island of San Giorgio in Alga, along the canal connecting Venice withthe Brenta river mouth.






When examining how ancient Venetians acted inorder to preserve their lagoon we can perceive appar-ent discrepancies. Sometimes, when the governmentfinally decided to realize important hydraulic enter-prises, such as massive excavations or river diver-sions, from the moment of the decision to the finalexecution a very short time elapsed. Just think – forexample – of the diversion of the lower branch of thePo, the greatest of Italian rivers. Once it became clearthat the easterly flows from the delta contributed tothe silting of the southern portion of the lagoon, itwas quickly decided to divert it to the south. TheSenate took the final decision in the year 1600 and ahuge excavation was completed in 1604, in spite ofthe delicate diplomatic problems that arose, thelower portion of the Po river being a political bound-ary between the Republic and the still powerful and

certainly not always friendly State of the RomanChurch.

Or just think of the huge sea-walls of Istrian stonealong the shores of the Lido: the work was begun in1740 and continued throughout the century with anenormous financial effort, in years considered, evenby recent historians, to be ones of political and eco-nomic decadence. The two opposing parties, activein Venice even in the past, of those who wanted toreclaim land along the borders of the lagoon andthose who wanted to leave the saltwater free toexpand as far as possible on the mainland, were inperfect agreement instead about the need for ade-quate protection along the seaward side of the lagoon.

But – this is the next question – have we everthought why it took centuries for the Venetians tocomplete not only other important hydraulic works

10 G. Caniato

Fig. 2.3 Aerial photograph of San Giorgio in Alga. Still visible are the recently collapsed remains of the ancientmonastery, used from 1810 until the Second World War as a military base (photograph by Giacomelli: Venice, 1960).






(such as the diversion of the rivers Brenta, Sile andPiave outside the lagoon, directly into the AdriaticSea) but also quite a simple operation such as the def-inition of the fiscal and judicial boundaries of thelagoon? The so called conterminazione (‘boundaryline’) was planned in the late sixteenth century andfinally concluded only in 1791, with different laws,regulations and prescriptions effective inside the line.Maybe one of the ancestral psychological reasons forthe delay was that the early borders – facing oftenhostile rulers on the nearby mainland – were alongthe uncertain line, varying with the tide, that dividedsalt lagoons (first home to the Venetians) from themainland and from the fresh water marshes occupiedby the new barbarians after the fall of the RomanEmpire. So the lagoons had to be maintained as wideas possible in order to keep the political and militaryboundaries far from the main inhabited islands. Yetat the same time ensuring that the tide could pene-trate deep inside the lagoon, in and out twice a day,to wash sewage away, keep the waterways healthyand the canals and channels deep. Diseases such asmalaria flourished in areas of prevailing fresh water– such as the surroundings of Torcello – that had to beabandoned. This long continued effort of theVenetians was encapsulated in the mid sixteenth cen-tury in a sonnet attributed to Cristoforo Sabbadino,the chief hydraulic engineer of the time:

Quanto fur grandi le tue mura il sai,Venetia, hor come le s’attrova vedi,

e s’al periglio lor tu non provedideserta e senza mura rimarai.

I fiumi e ‘l mar e gli huomini tu haiper inimici, e ‘l provi e non lo credi,

non tardar, apri gli occhi e muovi i piedi,che volendolo poi far tu nol potrai.

Scaccia i fiumi da te, le voglie ingordede gl’huomini raffrena e poscia il mare,

restato sol, sempre t’harà obedita.

(…)

How great your walls were, you knowVenice, now see how you find them.

and, if you don’t provide against their ruin,deserted and wall-less you will remain.

The rivers, the sea, and men you haveas enemies, and for proof and belief

don’t delay, open your eyes and get moving,(otherwise) what you wish to do, you will find

impossible.

Drive the rivers away from you, and check the greedydesires of men and then, only the searemaining, it has always obeyed you.

(…)

But why – this is the next question – were manyother projects concerning the safeguarding of thelagoon proposed, discussed, analysed, sometimesexperimentally started, but finally abandoned ornever realized? Projects, that became numerous espe-cially in the sixteenth and seventeenth centuries,such as those presented in 1672 to the Senate and tothe Magistrato alle Acque by Agostino Martinelli(Prodromus ad revocandam lacunam inclytae civitatisVenetiarum ad primam profonditatem), who proposedbuilding a stone wall across the sea-mouths of thelagoon, provided with huge sluice gates (…per le qualia compiacenza si potessero aprire e serare, hora per intro-dur il mare et hora per negarli l'ingresso) (which couldbe opened and closed at will, to let the sea in or tokeep it out) and in 1673 by Alfonso Moscatelli whoproposed closing two of the major port mouths(Chioggia and Sant’Erasmo) and separating withembankments the central lagoon from the marshesfacing the mainland, in order to strengthen the vitalnatural action of the tides.

So our ancient patrician rulers and water manage-ment technicians planned, studied, proposed anddiscussed dozens and dozens of projects, often mademistakes, tried to correct them by learning fromnature’s reactions, or just changed their minds overtime. Planning artificial diversions on the lowercourse of the Brenta river – as an example – went onfor centuries, starting long before Venice achieveddirect control of the nearby mainland. Padua ruledthe whole area through which the river ran until thebeginning of the fifteenth century but even in the

Between salt and fresh waters 11






twelfth century rivers had been diverted, mainly forstrategic reasons and not far from the boundaries ofVenice. Here swamps and marshes, scatteredamongst fields and agricultural land, were oftencompromised by river flooding. The river delta wasimportant not only for trade between the sea, thelagoon and the densely populated plains of northernItaly, but also for fishing, hunting, brush-wood gath-ering, heating and mill-grinding. All these activitieswere needed for the survival of the thousands thatcould make a living from the lagoon and from thenearby mainland and marshes.

Health problems caused by natural or anthropicchanges in the local environment forced theVenetians to act. In 1324, they decided to build along earth bank in front of the Brenta lagoon delta,

in order to divert the river to the south-west, as faras possible from the site of the capital. This enter-prise soon caused serious environmental problems,both to the nearby mainland, where fresh waterlakes and marshes expanded and forced peasantsto abandon their lands and houses, and to the mainsea-channels, which shallowed with the loss of thepreviously adequate and continuous river flow thathad kept them naturally deep. At the beginning ofthe following century the ‘filling up’ of the lagoon(today we know it was probably caused by a gen-eral lowering of the average sea level, but our fore-fathers did not have such scientific data) and thereduced depth of the main canals and harbours –so vital for maritime navigation – forced Venetiansto plan possible solutions.

12 G. Caniato

Fig. 2.4 A 1585 text painted on the inside wall of an anciemt warehouse on the Lazzaretto Novo island. Here wool andother goods were kept in quarantine (photograph by G. Caniato, 1978).






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