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A LONG the Pacific coast of Australia, just north of Sydney, Warringah Shire Council is preparing for the greenhouse effect. The local authority, which is responsible for 65 per cent of Sydney’s beaches, is worried about how a rise in the mean sea level, higher tides and extraordinary storm surges will affect its community of nearly 200,000 people and the district’s precious 25 kilometres of shoreline. It is particularly concerned about a 5-kilometre stretch from Collaroy to Narrabeen, which boasts beaches with real estate worth more than A$200 million (Pounds sterling 100 million).

The council has agreed to plan for one of the worst scenarios of our future climate. It accepts the view that greenhouse gases, which include carbon dioxide, methane, nitrogen oxides and chlorofluorocarbons (CFCs), are accumulating in the upper atmosphere at a faster rate than ever before; that this mixture is trapping the heat that is radiated from the Earth and causing global temperatures to increase significantly; and that the result will be a melting of the world’s glaciers and a swelling of its seas and oceans to unprecedented levels during the first half of the next century.

While the scientific community ponders and re-evaluates the evidence for global warming, Warringah Shire has adopted planning regulations that require entrepreneurs to consider the consequences of the greenhouse effect on proposed developments along the foreshore. Compensating measures range from higher ground floors in new buildings to restrictions on the use of low-lying land, which can mean golf courses or car parks instead of luxury homes or hotels. The council must also consider ways of protecting its foreshore and improving its drainage systems; pipe networks designed to cope with the sort of severe flood expected once every 50 years could be tested to their limits every 17 years after 2030, says Brent Gerstle, an environmental scientist who helped the council to draw up its strategy.

Few scientists agree on how high and how quickly the sea will rise. The generally accepted ‘best estimate’ is a rise of between 15 and 50 centimetres by 2030. According to Jim Titus, project manager in the Division of Global Change at the US Environmental Protection Agency, the increase could be anything between 50 centimetres and 2 metres by 2150. He stresses the need to consider a very long timescale when planning how land should be used. Over the next 50 years, he says, an increase of between 15 and 45 centimetres is possible. The imprecision reflects primarily the poor understanding we have of how the oceans influence the process of global warming. Furthermore, local subsidence could make some areas of the world more vulnerable to rising sea levels.

Titus’s view is not shared by Aksel Winn Nielsen, professor of geophysical science at the University of Copenhagen. ‘There are at present no indications that the rise is accelerating due to global warming,’ he says. Tide gauges have recorded sea level rises of between 10 and 15 centimetres over the past century and Winn Nielsen sees no reason why the trend should not continue for the next 100 years.

The rate at which sea levels will rise is also a source of contention. According to researchers from the University of Colorado at Boulder, the rise will be slower than some scientists have predicted. After a study on Ellesmere Island, the Canadian island near the North Pole, the team from the university’s Institute for Arctic and Alpine Research says that water from melting glaciers could take longer than expected to reach the oceans. It says that water percolating down through the permeable snowpack refreezes periodically en route in the underlying pores during chilly summer months, delaying runoff. This analysis contrasts with another by Michael Tooley, a geographer at the University of Durham. Tooley studied the stratigraphic record for the Ribble Estuary in northwest England over the past 10,000 years, since the end of the last glaciation; he has also examined the results of similar work in Canada and China. As a consequence, he suggests, there could be a potential for catastrophic flooding of the Earth that would raise sea levels by 23 centimetres in a few weeks or several metres in a few years (Nature, vol 342, p 20).

The contradictions and diversity of opinions do not bother Gerstle, however. He insists that the figures are almost irrelevant at this stage; the key to a practical approach to the greenhouse effect for local authorities is to ‘entrench a strategy, to have a policy in place and ready as the numbers change’. This view is endorsed in a report from the Intergovernmental Panel on Climate Change that urges governments to begin identifying regions at risk from rising sea levels (‘Rising sea levels could affect 300 million’, This Week, 20 January 1990). The report will be presented in November in Geneva at the IPCC’s conference on environmental change.

In Australia, at least, Warringah Shire is not alone. Since 1986, when Salisbury Council in Adelaide decided that new developments should be protected from a sea level rise of 40 centimetres in 50 years, more and more local authorities have begun to take the greenhouse effect seriously. There have been setbacks. In 1988 the Planning Appeal Tribunal in Victoria overturned a decision based on Warrnambool City Council’s new strategy for dealing with global warming; it ruled that a developer could build on land that the council said would be inundated as a result of the greenhouse effect. The tribunal decided that there was not enough evidence to support the council’s case. Gerstle says the tribunal’s ruling reflects a reluctance among many decision makers to incorporate scientific matters in medium- and long-term plans.

The mood seems to be changing rapidly. The Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia’s largest research body, is now coordinating data on sea levels in the Pacific region to ensure that the information comes from a broad spread of locations around Australia as well as from the island nations of the South Pacific. This will help councils that need more specific, local data with which to defend their strategies. In December 1988, the Australian Marine Sciences Association made a policy statement that set out the background and environmental impact of the greenhouse effect, highlighted the need for more information and recommended action to mitigate the consequences of global warming. In June last year, the state government of Victoria published The Greenhouse Challenge: A Draft Strategy for Public Comment, and by August, the Institution of Engineers, Australia, had defined its Policy on the Greenhouse Effect. In its document, the institution says that it ‘recognises the need for engineering practice to take into account the potential impacts of the Greenhouse Effect and accepts the responsibility to provide guidance to the profession on adaptation to these impacts’.

Such an unequivocal stand is rare. While the world’s meteorologists, oceanographers, geologists and atmospheric scientists talk among themselves, dismissing their early forecasts of the consequences of the greenhouse effect and devising better mathematical models of climatic change, many local authorities feel they have little option but to ignore the issue altogether. Others complain of scientists’ obsession with refining their predictions while what municipal planners and engineers need is a little more guidance on how to formulate a practical response to global change.

¿ìè¶ÌÊÓƵs and city planners gathered in Venice in December to air their grievances and to exchange ideas of ways to cope with conflicting scientific advice. Venice presented the event as the first international meeting of the ‘Cities on Water’, an organisation established in March last year by the local municipality, university and institute of architecture, and by the consortium of Italian contractors that is building the barriers to protect Venice from flooding. The organisation aims to bring together town planners from threatened regions, and their consultants, to exchange knowledge and experience of coping with rising water levels.

A particularly difficult time awaits those islands in the Pacific, Indian and Caribbean oceans, whose land is already in short supply. The small island nations simply cannot afford to let the oceans encroach on their heavily populated cities, which often provide the only hospitals, secondary schools, services and industry. According to John Pernetta, who has been studying the island nations of the region for the UN Environment Programme, the atoll state of the Maldives faces an extremely precarious future. The highest land in the country is only 3 metres above sea level, and around 56,000 people live on Male, the island capital that is just 1700 metres long by 700 metres wide. The state needs help if it is to mitigate the effects of rising sea levels, and yet recent examples of international assistance give more cause for concern than for comfort. The aquifer that provides Male’s drinking water will run dry in 1993; international aid agencies propose to donate desalination plants but, as Pernetta points out, the plants will cost $48 million a year to run, which is more than the state earns in foreign exchange.

Pernetta also highlights the reclamation project that gave the citizens of Male more space but buried the coral reefs that protected them from storm surges. Artificial protection, in the form of new breakwaters, cost as much as $8000 per metre to install. Preserving the natural reefs would be cheaper (‘Gone with the waves’, ¿ìè¶ÌÊÓƵ, 11 November 1989).

The need to find ways of fortifying vulnerable stretches of coastline without unwittingly causing more problems now occupies the minds of the planners looking for lasting solutions. The term they use to describe what they want is ‘soft engineering’, as opposed to the ‘hard engineering’ of installing groynes and building massive flood barriers. Groynes may stop beaches moving down the coast but they can cause serious erosion locally, and flood barriers create artificial environments that can, for instance, change tidal flows and damage local ecosystems.

Titus highlights the problems in the Mississippi delta of Louisiana, where every year 100 square kilometres of marshland become open water; by 2030, he says, the coastline could be at the southern outskirts of New Orleans. The local seafood industry has not complained; the encroaching Gulf of Mexico temporarily improves the shrimp catch, while a decision to protect the marshes by reclamation would ruin the industry’s oyster beds. Traditional engineering in the delta has not helped to preserve the region either. In the last century, dykes were built to protect against floods, and more recently, to maintain deepwater shipping lanes to the Port of New Orleans. By increasing the flow of the Mississippi river, the dykes have encouraged sediment washing down the river to travel out to sea and over the continental shelf instead of settling and helping to maintain the delta.

‘Louisiana is an area that didn’t worry about what would happen,’ says Titus. ‘Individual actions worked in themselves, but overall they created a problem.’

He concludes that the region must now restore the natural processes that maintain the delta to prevent further erosion of the territory. This ‘may require overhauling the current system of navigation channels, rerouting the river, and rebuilding the Port of New Orleans a few dozen kilometres to the east of its current location’.

One of the leading proponents of the concept of soft engineering is Ronald Waterman, a local politician and an environmental adviser to the Dutch public works department, the city of Rotterdam and several engineering organisations. The Netherlands is the site of one of the world’s most extravagant and intrusive flood protection projects, the storm surge barrier across the Eastern Scheldt estuary. This defence against the North Sea is a marvel of civil engineering and, at a time of recession and rationalisation in the construction world in the late 1970s and early 1980s, it kept the Dutch industry buoyant.

But the project was the focus of environmental protest from the moment plans for it were first aired in the mid 1970s to its completion in 1987. Much of the money allocated to the project was spent on ensuring that the barrier, 3.2 kilometres long across the estuary’s mouth, did not damage the ecology of the area. And although Dutch firms gained unique expertise in marine engineering, which they hoped would win them valuable construction contracts internationally, they earned little more than prestige in a world that was beginning to seek environmentally friendly solutions to coastal problems. ‘We are no longer looking for strong sea defences; we want a flexible coast in dynamic equilibrium,’ says Waterman. He advocates coastal management projects that exploit natural processes to preserve the shoreline.

Waterman’s solution for the Eastern Scheldt would have been to raise and strengthen the dykes along the banks of the estuary. This would have been cheaper and less intrusive than installing the barrier but it would not have truly fitted his concept of ‘building with nature’. His plans for protecting the North Sea coast of the Netherlands involve altering the alignment of the shoreline by extending the beaches, laying down dunes and burying an established series of groynes. He says it is possible for accretion and erosion of a coast to more or less balance each other so that maintenance, or ‘beach nourishment’, becomes necessary less often, perhaps something that is required every four or five years.

Work in the Netherlands to Waterman’s plans began in the 1970s on a battered stretch of coast from Scheveningen, 21 kilometres southwards to Hoek van Holland, at the mouth of Rotterdam harbour. The new foreshore will have a wedge shape covering 3000 hectares; it will extend a few metres from the original shoreline at Scheveningen and to 3.5 kilometres at Hoek van Holland. This will change the orientation of the eroding stretch and make the shoreline more convex. When the scheme is completed, the coast should be able to survive without groynes. So far, only 100 hectares at the thin end of the wedge have been laid but the job should be finished by the end of the century, says Waterman. It will have cost Pounds sterling 400 million, paid by both public and private sponsors. Although there are no immediate plans to implement more of Waterman’s scheme for the rest of the coastline, which stretches for 200 kilometres, his ideas are echoed by planners from Australia, the US and the Mediterranean region.

Barriers to progress

But some cities do not have the time, the resources or the inclination to draw up strategies for coastal management that rely on natural processes. An artificial barrier across the River Thames protects London; another is nearing completion in the Neva estuary to safeguard Leningrad; and Venice hopes to be able to close the three mouths of its lagoon with steel gates by the end of the century.

One of the problems with artificial barriers is that often they cannot be modified easily to withstand harsher conditions. The Thames Barrier is designed to work until the middle of the next century, by which time we will be able to gauge the accuracy of predictions about rising sea levels. If London needs a higher barrier, the city will have to build a completely new structure; the present one consists of a series of gates with little between them, which provides no foundation for raising the structure. This is not the case in Leningrad, however, where the 25-kilometre barrier has eight gates separated by long stretches of earth embankment. According to Yuri Sevenard, who is in charge of building the Soviet barrier, the city can raise the height of the barrier without difficulty to provide extra protection. In Venice, the political wrangling that is delaying completion of its barriers has at least ensured that the engineers designing the new barriers do so with the very latest estimates of the consequences of global warming in mind.

Among the cities with a most pressing need for protection is Hamburg. According to Gert Ascher, chief planner in the state government’s Ministry of Construction, the city must devise a strategy for safeguarding its future within three years. Even then the defence works will take at least 25 years to complete. The problem for Hamburg is that although the city lies 120 kilometres from the North Sea it sits on the River Elbe, whose water level fluctuates considerably. As it narrows, the river acts like a funnel, lifting tides 70 centimetres higher than they are at the coast, and as much as 1.8 metres higher during exceptional flooding. Widening and deepening the river in the early 1980s to provide shipping lanes has also caused problems, increasing the volume of water that can pass along the river and reducing the effect of friction at the seabed in slowing down the flow. These features alone have led to a rise of 10 centimetres in the mean tidal high water level in Hamburg.

After 1962, when a flood claimed 315 lives and made 20,000 people homeless, Hamburg raised its defences from 5.7 metres to between 7.2 metres and 9 metres above mean sea level. After a near catastrophe in 1976, when water rose to 6.45 metres above mean sea level, private and public enterprises in the city raised their lowest defences another 30 centimetres, to 7.5 metres, and commissioned a thorough analysis of the local flood risk. This analysis revealed that rising water levels threatened 320,000 people in the city area, more than 200 square kilometres of land and a bill for damages of DM16,000 million (Pounds sterling 5500 million).

Other factors make Hamburg more vulnerable to flooding. One result of raising and strengthening dykes along the banks of the lower Elbe, which began in the late 1970s, is that water that once flooded land downstream now reaches the city. This has raised the mean tidal high water level by between 40 and 50 centimetres. Finally, the West German shoreline is slowly subsiding, although so far movement has been detected only along the northeast coast.

As a result, Hamburg has begun a programme of defence works to raise the most vulnerable stretches of flood banks by 50 to 80 centimetres. The detail of a more extensive programme of works, which will raise flood banks at least another 15 centimetres, is still being decided. The improvements are expected to cost as much as DM4000 million.

While some planners despair at their isolation and lack of information about how global warming might affect their territories, some scientists in the US have chosen an unusual way to raise awareness of the issue. Tunney Lee, head of urban studies and planning at the Massachusetts Institute of Technology, offers two scenarios for a Boston of the future. ‘It is the year 2050. Global warming has raised water levels 50 centimetres. A typhoon at the high tide has struck.’ Boston is under martial law, says Lee, while looters and rioters fight over food and water, telecommunications fail, major highways become inundated, sewers block and thousands of homes, factories, offices and schools are severely damaged or destroyed. There is an alternative, he suggests. The city, having prepared for a catastrophe, faces a difficult but survivable period of adjustment. ‘At additional cost, it had built its major roads, water and sewer lines, telecommunications channels . . . above high water levels. After acrimonious debate and opposition from business and builders, it had banned building on land vulnerable to flooding. . .’

Further reading: Impact of Sea Level Rise on Cities and Regions, from International Centre ‘Cities on Water’, S. Marco 875, 30124 Venice, Italy.