OFFSHORE cities, each with a population of 30,000 or more, and providing all the facilities and amenities of land-based ones, seem like a fantasy from science fiction, yet they could become a reality in a matter of years.

Detailed plans for such man-made island centres have been produced, and some authorities see this idea as an answer to the problems besetting the world as a result of the everincreasing population. Within the foreseeable future the great oceans of the world, together covering no less than three-quarters of the world's surface, must inevitably carry industrial centres and afford a permanent home to some of the population.

Civil engineers, scientists, and other experts have been tackling the problem, and have produced a project for sea cities in various parts of the world. Moreover, they have built a scaleddown prototype, showing what such a city would look like and demonstrating the amenities it would provide. This model is envisaged as representing a city in the North Sea, but shoal water covers nearly one-tenth of the world's seabed, offering many suitable sites for developments of this kind.

The North Sea site selected for the present project is 15 miles offshore from Great Yarmouth.

The blueprint shows a 16-storey amphitheatre on piles, with a central lagoon warmed by waste heat from the city's industries.

Clusters of floating islands carry houses, schools and public buildings.

The main structure is protected on the seaward side by an encircling breakwater, and this outer structure is broken at one point—at the south-east corner, to provide a narrow harbour entrance. To create the real city, piles brought from the mainland would be driven into the seabed in rows, 20-30 feet apart, to form the base structure. Reinforced concrete deck sec-tions, precast ashore, would be towed to the site, jacked up on guide rails between the rows of piles, and then locked in position at the top of the piles to form a continuous slab.

Resting on the completed base, and starting 30 feet above sea level, the superstructure would consist of concrete cells joined together at the corners and mounted one above another on spacer units. These spacers would form ducts for gas, water, electricity, and sewage. Each concrete cell unit would be stressed down on to the one below, thus forming a completely stable structure like a monster stone block.

The islands in the lagoon would be made up with triangular concrete pontoons 60 feet wide, and held in position by anchor chains. Linked by flexible couplings to allow for water movement, these rigid sections could be easily separated and re-coupled to form islands of different shapes and sizes. The top platforms would carry lightweight glass-fibre reinforced plastic buildings up to three storeys high.

The North Sea city would incorporate a number of intriguing features, including measures to control winds and rough seas. A wide 'moat' of calm water, created by a protective breakwater, would surround the site.

Cylindrical coated-fabric bags, 90 per cent, full of fresh water and lying side by side, would form the breakwater.

The bags would be anchored fore and aft in groups of three, and would be allowed to float awash. Then, when struck by an oncoming roller, they would generate a secondary, rebounding wave inside. This wave, rebounding against the end of the bag, would meet the following sea and protect the outer walls of the city.

Another idea, to maintain the calm of the inner lagoon in bad weather, would be to create a curtain of compressed air bubbles across the entrance by means of undersea pipelines, thus breaking up the waves still more.

The 180-foot high curved wall of the amphitheatre has been designed to protect residents of such an oean city from wind. Its shape—like a monster letter 'S' leaning slightly outwards— is the result of wind tunnel tests at Leicester University. They have shown that the shape deflects the wind upwards and leaves the area below relatively calm.

The blueprints foresee the city being supplied with natural gas from under the North Sea.

High-speed gas turbines would be coupled to generators producing electricity, and waste heat from the turbine exhaust gases would be used to run the sea-water desalinating plant, as well as for domestic and industrial heating and refrigeration. Finally, the hot cooling water would be emptied into the lagoon to raise the temperature of the water there.

About 21,000 residents, most of them daily commuters between the sea city and the mainland, would have their homes in the 16 storeys of the terraced city wall. Other inhabitants would have individually designed houses on islands, these homes having up to seven rooms and most of them adjoining a terraced garden.

The city would, in fact, be much more than just a dormitory for people who work on the mainland. It would include shops, clubs, restaurants, gardens, and churches for different denominations. These, like the flats within the city wall, would be served by escalators, moving pedestrian pavements, and covered walkways.

Internal travel, and commuter journeys to and from the mainland, have also been carefully worked out. The project provides for electrically-powered boats and water buses to operate within the city, the bus service being at five minute intervals and making a circuit (with stops at strategic points) in 25 minutes.

Visiting craft would not be allowed to enter the inner lagoon, but would be moored outside the city wall near the lagoon entrance.

Specially designed articulated container ships would bring supplies from the mainland, and ample storage would be provided, although the residents are unlikely to be cut off for long periods. Even now, hovercraft can travel safely at 30 knots in strong winds and over 10-foot waves.

Commuting between the sea city and the mainland would be by helicopter or helibus.

The latter type of aircraft is still undergoing development, but such a plane would take off and land like a helicopter. Once in the air, however, the rotors would fold into the top of the fuselage, and the plane would then continue its flight like a conventional fixed-wing aircraft.

The social life of this city of the future would follow the lines of many land-based places, as would the municipal services, Nursery, primary and secondary schools would be among the public buildings on the floating islands. A onemile walk would take residents to any part of the city via a network of footpaths and bridges across the islands.

The medical service would include a 200-bed hospital, clinics, and dental services. The city would become part of the Post Office communications network by telephone and telegraphic underwater cables running to the mainland.

Social and cultural facilities envisaged for the ocean city include community centres, open air tea-gardens, youth clubs, theatres, libraries, cinemas, an art gallery and a museum.

There would be provision for sportsmen of all ages, the centre basin of the lagoon being reserved for water sports, during a season lengthened by the artificially warm climate.

Tennis courts, bowling greens, netball courts, croquet lawns, and even a full-sized football pitch would be provided, too.

The football ground would be on top of the power complex.

A permanent offshore centre like this would be important in developing specialist marine industries. A college of marine studies here— with submarine laboratories, observation post in a marine zoo, and on-the-spot research vessels—is seen as a first step towards a University of the Sea and an international centre for oceanography and underwater studies. And most certainly a Y.L.A. office.

In the war against world food shortages, sea cities could make a big contribution by being centres of efficient fish farming industries.

Investigators report that the yield from such a farm would at least equal that of any similar sized warm water farm operating in America or Europe, where an acre normally produces five tons of fish a year.

In recent years, roads have been built across bays, and other projects no less demanding than the sea city idea have been carried out successfully.

Sooner or later, sea cities may offer the only answer to the shortage of living space..