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ON THE afternoon of 31 January, earlier this year, Raymond Latchmansingh received a radio message from one of his foremen in Berbice, Guyana’s easternmost region. Some 200 metres of the wall that keeps the Atlantic Ocean out of the sugar estates of the Skeldon area had collapsed. Latchmansingh’s unenviable task, as chief hydraulics officer of Guyana’s Ministry of Agriculture, is to save this South American country from being swallowed up by the ocean. ‘One can expect a breach at any time,’ he said. ‘Today I received reports of two breaches in West Demerara and three breaches in Berbice. The wall at Skeldon protects a lot of the sugar estates, so if we don’t seal it soon, salt water will destroy the cane.’

Guyana cannot afford to ignore the sea. Not only is sugar the mainstay crop of Guyana’s economy, but 90 per cent of the country’s 750 000 people live on the long, thin coastal plain that makes up less than 3 per cent of the total area of Guyana. This narrow strip, 500 kilometres long and never more than 16 kilometres wide, contains the most fertile soils: the rest of Guyana, apart from some of the Rupununi savannah in the southwest, has very little potential for agriculture. All the agricultural production and other economic activity, apart from mining, is concentrated in the coastal plain, which produces more than 70 per cent of the country’s gross domestic product. Unfortunately, this important land lies below sea level at high tide and is liable to flooding and erosion by the sea.

Coastal protection, however, is expensive. Until the mid-1970s, sea defences, drainage and irrigation ate up more than a third of Guyana’s capital expenditure. Then the country’s economy went into rapid decline after the government nationalised the major industries. The GDP has declined by 6 per cent each year since 1980, and exports are now 20 per cent lower than they were in the mid-1970s. At the end of 1988, Guyana owed its international creditors $800 million. Shortage of foreign exchange has affected every part of Guyanese life, including the maintenance of the sea defences built over the past two centuries by the Dutch and the British . Almost half of the sea defences are past repair, says Latchmansingh. ‘It’s not a question of maintaining any more. It’s a question of replacement.’ Large sections of the walls are collapsing, and roughly 170 kilometres of the 500-kilometre coastline needs new permanent structures to be built, with 130 kilometres in dire need of replacement.

As if there were not enough to worry about, the predicted rise in sea level from the greenhouse effect promises to intensify Guyana’s struggle with the Atlantic Ocean. The Commmonwealth Secretariat has just completed a study of the implications of the greenhouse effect for Guyana and other low-lying countries and small islands which, as former colonies of Britain, belong to the Commonwealth of Nations. The aim is to suggest strategies for protective measures that could ameliorate the effects of a rise in sea level for countries such as Bangladesh and Guyana and the Pacific atolls of Tonga, Kiribati and Tuvalu. Investigations for the report on Guyana in the study were carried out by Robert Camacho, an engineer who was Guyana’s chief hydraulics officer and is now a consultant to the Commonwealth Secretariat.

There is still no consensus among scientists about the rate and extent of a rise in sea level. Estimates range from 13 to 38 centimetres by 2025, and anything between 0.5 and 3.5 metres by 2100. The generally accepted ‘best estimate’ is for a rise of between 15 and 30 centimetres by 2030 (‘Cities against the seas’, ¿ìè¶ÌÊÓƵ, 3 February 1990). Camacho considered the vulnerability of Guyana to three rises in sea level from 1989: 0.25 metres by 2020, 0.5 metres by 2040 and 1.5 metres by 2090. His study found that much of the coastal strip where most of the people live would be well below mean sea level following a rise of half a metre, although a large part of the agricultural lands would still be above mean sea level. A rise of 1.5 metres, Camacho writes, would affect virtually the whole agricultural area.

Without improvements to the present sea defences, Camacho predicts that more breaches would soon occur and sea water would overtop the walls and embankments. Soils would become very salty and could no longer support cultivation. Agroindustry would collapse as sugar factories, rice mills and other smaller industries were forced to close. Homes on the coast would become uninhabitable as water supplies, sewers, power supplies and telecommunications stopped working because of constant flooding. The cost to the country would be enormous. Camacho estimates that a rise of 1.5 metres in the sea level could wipe out US$107 million in annual revenue from the sugar industry, $46 million from rice, $84 million from other crops and $11 million from livestock. The loss of rent from housing at threat from rising sea levels could add up to almost $540 million a year. The total effect on the coastal plains could be to destroy almost $800 million of economic activity.

Lack of resources

The hydraulics division of Guyana’s Ministry of Agriculture has barely considered the grim spectre of the greenhouse effect. Latchmansingh is struggling merely to cope with the day-to-day demands of coastal protection. ‘I wouldn’t like to say that today (31 January) is typical of any other day, but anything can happen given the present state of the sea defences,’ Latchmansingh said. Materials and equipment are old, too, and in bad repair. The list of needs is comprehensive: steel sheet piles, polypropylene fabric, filter fabric, draglines, cranes, dumpers, concrete mixers, and spare parts. All have to be imported and paid for in foreign currency.

Mahadeo Persaud, the acting deputy to Latchmansingh, said that the breaches, although frequent, have yet to cause serious damage. There has been no loss of human life, minimal loss of livestock and negligible damage to property. While Persaud has the expertise to carry out effective emergency repairs, he points out that he is ‘the only officer in the department with postgraduate training (in coastal engineering)’. Most of the engineers are young graduates with no more than two or three years’ experience; another 10 officers, superintendents and foremen have practical experience but no specialist knowledge. Persaud says that the department needs more ‘skilled manpower, people who have the technical expertise, who know what to expect from the sea and what types of defence are necessary to secure the coastline’.

Some relief has come in the form of a grant from the EEC, which has given Guyana $6 million for a three-year programme of work on its sea defences beginning this year. As part of the deal Guyana must match the EEC input. The US has also agreed to provide a further $9 million for the programme. But these sums will cover only work that Latchmansingh classifies as emergency: those sea defences that literally collapsed. This will offer protection for only a short period. ‘We really need to embark on a programme to give protection over a 50-year span,’ he says. To install that type of protection, he predicts, would cost about $2000 a metre. To replace even the worst 130 kilometres of the coastal defences would take $260 million. That is money that Guyana simply does not have.

Sea walls, though, may not be the best answer to coastal protection, according to Chris Fleming, head of coastal engineering projects at the British civil engineering consultant, Sir William Halcrow and Partners. The company worked on a sea defences project in the vicinity of the Essequibo River between 1979 and 1984, as part of an Pounds sterling 3.25 million aid package from Britain’s Overseas Development Administration. ‘The best coastal protection you can have in Guyana is a long, sloping foreshore, leading to mangroves and a small earthen dam behind that,’ says Graham Cook, who managed the Essequibo project for three years. Cook’s prescription describes Guyana’s natural coastal protection. Its foreshore stretches out to sea, sometimes for 5 kilometres or more, and mangroves at one time protected large parts of the coast. The web-like roots of the mangroves dissipate much of the energy of the waves. To the landward side of the mangroves is a swampy area. The water here is calm, gently rising and falling with the tides. All that the early Dutch settlers needed to build was a small earthen dam, about 1.5 metres high and 4 metres wide at the crest, to prevent the gentle waves flooding the adjacent agricultural land.

Two things have affected this natural protection, however. The first, and most recent, is that lack of cooking fuels has forced people to cut mangroves for fuel wood. The second is a phenomenon of mud shoals that move along the coast in a cycle of erosion and accretion. The mud emanates from the Amazon River, and possibly other rivers, and currents sweep it along the coast. The Guyanese refer to it as sling mud. The chemistry of the particles is such that they are always in suspension: the mud never consolidates. A detailed study carried out by the Netherlands Engineering Consultants (NEDECO), and published in 1972, suggests ‘macro ripples’ of sling mud destroy the mangroves by eroding their roots. As the mangroves die and collapse, waves hit the earth dams with their full force. When this happened, engineers strengthened the seaward sides of the dams with concrete. Earthen dams eventually turned into sea walls.

According to Latchmansingh, it costs too much to build a sea defence to keep all the water out. Guyana, therefore, built its sea walls so that the crests are 1.2 metres above the height of a 1-metre wave at high water. This prevents excessive overtopping: on a 1-metre section of the wall no more than than 1 litre of water per second should come over the top. If the sea level rises by 1 metre, however, the wall will be only 0.2 metres higher than waves at high water. This might lead to about 5 litres per metre per second of overtopping, which Latch mansingh believes will have a devastating effect on crops.

Time to invest

‘The government of Guyana,’ says Latchmansingh, ‘must obtain the necessary resources to accelerate the programme for sea defences.’ It cannot afford to allow the coast to flood and to evacuate the inhabitants: the interior of the country is largely infertile and mining, the only other major industry, is still in its infancy. The only option is to protect the coastline. Latchmansingh estimates that Guyana needs at least $200 million over the next five years to make the sea defences safe. Among his priorities are more training for his engineers, and money to buy equipment and materials: concrete, mixers, dumpers, cranes, steel and so on. Four-wheel-drive vehicles and a helicopter would also allow his team to respond more quickly in emergencies. He also wants a hydrographic vessel so that his department can monitor accretion of sling mud and erosion along the coast.

The NEDECO study identified a 30-year cycle of accretion and erosion along the Guyana coast. According to the study, the net effect of the cycle is that the Guyana coastline is retreating. It predicted which areas of the coast are likely to be eroded and suggested that sea defences were rebuilt in those areas. But another study, carried out in 1978 by Britain’s Hydraulics Research Station, based at Wallingford and now known as Hydraulics Research, concluded that the process of erosion and accretion of sling mud was much more complex than that described in the NEDECO study and could not be accurately predicted. It found no evidence of erosion at the points along the coast predicted by NEDECO.

Camacho proposes an investment programme lasting 30 or 40 years to protect the fertile coastlands from the predicted increase in sea level from the greenhouse effect. This would need to be funded from international agencies. The first stage of such a programme, lasting five years, Camacho has costed at $21.5 million. Of this, $17 million would be needed for surveys and for equipment, materials and vehicles for rebuilding embankments, sea walls and revetments. The remainder would cover labour, maintenance and overheads.

Meanwhile, Camacho recommends that Guyana wastes no time in seeking technical and financial assistance so that it can commission follow-up studies. For example, it should identify the most vulnerable parts of its coast and the options for enhancing coastal protection and drainage so that engineers and planners have as much time as possible to consider all possible strategies. Other studies should monitor climate and sea level. The country should also investigate the mangroves on the foreshore, and how to reintroduce and conserve the vegetation to provide some natural protection. Vincent Cable, a special adviser at the Commonwealth Secretariat, describes the Camacho study as as ‘an excellent basis for an adaptation strategy in respect to sea level rise which an imaginative donor should take up. We hope that bodies such as the World Bank and Inter-American Development Bank would do this.’

Despite the many difficulties, Guyana is at least managing to keep abreast of current thinking on sea defences and technology. Latchmansingh has just appointed an aquatic biologist to study the regeneration of mangroves, and the hydraulics division has begun a public education campaign on the radio to discourage people from destroying the coastal vegetation. ‘The mangroves may give us 10 years protection in certain areas. We are buying time,’ he says.

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Evolution of a wall against the sea

YOU CAN see most of the recent history of sea defence design travelling along the coast of Guyana. The uninhabitable swamps and mud shoals that characterised the coast of Guyana forced the Dutch in the 17th century to settle inland along the banks of four rivers: the Essequibo, Demerara, Berbice and Corentyne. By the middle of the next century they had exhausted the soils along the river banks. They used the knowledge and experience of their own country to reclaim the coastal swamps, which provided them with fertile agricultural lands. They built a network of drainage canals, sluice gates (kokers) and sea walls along the same lines as those in Holland.

In 1841 Britain purchased the Dutch settlements, and formed the colony of British Guiana (the colony became independent Guyana in 1966). The British followed the example of the Dutch and built similar sea defences. As mangroves declined and waves reached the embankments, they reinforced the earth dams with wood and then steel. This century, concrete replaced wood, and the design of the walls became increasingly sophisticated.

Some of the concrete walls are smooth, others stepped. Curved and sloping upward, they rise to concrete copings (or wave screens) of various shapes. At the bottom of the wall, a concrete slope, or revetment, stretches down towards the sea. At the ‘toe’ or seaward end of these revetments, steel piles sunk into the mud help to resist waves that would otherwise erode the foreshore from under the revetments. Waves reflected back from the sea wall would also scour the toe.

But the sheet piles only delay erosion. Another problem stems from the sling mud underlying the concrete revetment, which normally does not consolidate. Under the weight of the concrete walls and revetments, however, the mud does consolidate, the concrete slabs settle, crack and, eventually, the wall collapses.

Monitoring the toe of the walls and the revetments for signs of erosion or settlement, and rebuilding the affected sections, would have lengthened their lifetimes. But Guyana is one of the world’s most heavily indebted countries. Recognising the country’s problems, Graham Cook, project leader for the British consultant Sir William Halcrow and Partners on the Essequibo Sea Defence Project, suggested dispensing with the conventional concrete sea walls and revetments. He proposed a cheaper and more appropriate technology based on the ‘rip-rap’ design, which relies on boulders to dissipate the energy of the waves.

Cook’s design employed a geotextile, in this case a tough synthetic polymer, buried in the 1 in 3 slope. The polymer is permeable to water but not to the particles in the sling mud nor to the fine sand of the foreshore. It therefore acts as a filter, preventing the loss of fine material underlying the revetments as the waves recede. Cook covered the polymer with 1-metre layer of crusher run, small stones readily available from Guyanese quarries. On top of this he placed granite boulders, also taken from Guyanese quarries. He replaced the expensive steel piles at the toe with large boulders of granite. Only the geotextile had to be imported. The boulders are surprisingly effective at dissipating the energy of the waves. By the time they reach the vertical sections of the wall they have no force.

Mahadeo Persaud, acting deputy chief hydraulics officer in Guyana, has modified the rip-rap design to make it even cheaper, and also uses it to repair small sections of sea wall that have collapsed. The essential changes are that his slope is less steep, there are fewer boulders and the geotextile is replaced. Persaud’s substitute for the filter layer is 30 centimetres of loam covered with 30 centimetres of white sand and then 30 centimetres of crusher run. The boulders are then placed, 8 tonnes per foot, on top of these layers. ‘Rip-rap results in the accretion of sand and sling mud between the boulders. We are building up the foreshore at the same time,’ Persaud explained.

Up to the mid-1980s, rip-rap looked like the cheapest and most effective answer to Guyana’s problem of sea defence. The rock is abundant in Guyana, as is the loam and white sand. But the price of locally quarried boulders has increased threefold between 1985 and last year.

There is now, said Latchmansingh, very little to choose between building rip-rap and concrete sea walls. Persaud, however, remains convinced of the superiority of rip-rap defences: ‘Rip-rap is everlasting.’ His view is borne out by the section of rip-rap that Halcrow built in the 1970s, which still shows no sign of deterioration.