The term reclamation applies both to the rework­ing of land that has been damaged by people - as a result of mining, for example - and also to land won from the sea.

The principles and techniques of land reclamation vary according to the setting, but the common reason is that land is a scarce and valuable resource which should be made available for productive or beneficial use wherever possi­ble.

Reclaimed land can be used for agriculture - for arable or pastoral farming - as sites for new towns and villages, for transport systems such as new airports, harbor facilities or road networks) and for industry.

Usually the most pressing need is for more living space, and many of the world's most ambitious reclamation schemes have been carried out in countries (such as the Netherlands and Japan) that have high population densities.

Reclaiming Land from the Sea

The most spectacular schemes to reclaim land are those that have been carried out in coastal zones. In the Netherlands, land has been reclaimed from the sea since the seventh and eighth centuries when the first dykes were built in Zeeland and Flanders, and about a quarter of the present land area of the country has been created in this way.

At first earth embankments or dykes were con­structed to enclose shallow, sheltered areas of water, and wind-driven pumps were installed to transfer the water from the enclosed lagoons into drainage channels.

More recently, and on a much larger scale, the Zuider Zee project was begun in the 1920s. A barrier dam was built to enclose the Ijssel Meer so that it could be turned into a freshwater lake, and several areas behind the dam were drained and eventually brought into agricultural use.

These reclaimed areas, called polders, lie below sea level and require continual pumping and protection from encroachment by the sea.

Other, less ambitious, forms of land reclama­tion have been carried out on the other side of the North Sea, in eastern England. Some areas of coastal marsh (which lie just above mean sea level, but are at least occasionally inundated at high tide) have been protected by earthen sea walls. In this way the marsh is cut off from salt water and, as happens in the Dutch polders, any remaining salt in the soil is gradually washed out by the rain.

Grass is planted eventually and after some years of grazing cattle or sheep the soil may be suitable for crops, and heavy yields can be obtained from the fertile, silty soil. Land reclamation from the sea has been on only a small scale in England, but has been carried out to such a large extent in the Netherlands that new farms, villages and road networks have been established on land that was once permanently under salt water.

Reclamation of land from the sea has also been carried out elsewhere in Europe: in Belgium, northern Germany and Denmark, north-western France, and in parts of the Mediterranean.

In Italy, the scale of the operation has been larger than in the Netherlands; reclamation has been concen­trated in the deltaic areas of the Adige, Po and Reno rivers, where the Plain of Lombardy meets the Adriatic Sea. A large reclamation project was also completed in Japan in 1966, using Dutch technical aid. The new polder is now densely settled and used for rice growing and fish farming.

Reclamation of Wasteland

The reclamation of land that is laid waste by min­ing or industry poses quite different problems. Such waste materials are often rocky and infertile in nature, and in the absence of a proper mantle of soil, it is difficult to establish a vegetation cover.

Rock waste usually holds little water, and plant nutrients are often either unbalanced or totally absent. Wastes from mining or the processing of metals such as copper, zinc and lead may be toxic. In the lower Swansea valley in Wales, for exam­ple, waste tips are still toxic as a result of non-fer­rous smelting activities in the past two hundred years, though much has been accomplished in recent years to clean up the area.

The reclamation of land damaged by poisonous waste is usually a slow and costly process. Gener­ally the most effective treatment is to spread a layer of good soil on top of the rocky waste.

If top-soil is available from a neighboring development site, then in one operation a fully developed soil of adequate structure, texture and nutrient status can be quickly established. But to be really effec­tive, a blanket of at least 10cm of topsoil is required on the waste; if trees and shrubs are to be grown on the reclaimed area, a far greater thickness is needed.

Because of the cost and lack of availability of topsoil this treatment is not always possible, and other less effective solutions may have to be employed.

Sewage sludge, pig slurry or peat may be used to improve the fertility of the soil, and in some cases one waste material is used to counter­act the damaging effects of another.

Hydraulic seeding - the application of grass seed mixed in water with fertilizers and soil stabilizers such as latex - may also be used in the treatment of sloping banks of waste material, for example, or on exposed land which is suffering from soil erosion.

Desert Reclamation

Many arid and semi-arid regions have fertile soil the potential of which for supporting crops is not achieved because of the lack of water. But in the Middle East, for example, traditional methods of irrigation have been used to cultivate land such as pumping up water from wells sunk into wadi beds. In addition, many desert areas, such as the Negev desert in Israel, have a heavy dewfall which is sufficient to be collected and used to water plants. More sophisticated methods of irrigation include water-carrying pipelines.