Land reclamation makes otherwise inaccessible areas available for human use. Swamps, deserts, and submerged coastal lands are naturally inaccessible; surface mines, waste-disposal sites, and municipal landfills are waste areas created by human activity. The land reclaimed from such areas has been used for agricultural and forest crops, recreation, wildlife, and industrial or residential development.

RECLAMATION OF NATURALLY INACCESSIBLE AREAS

Naturally inaccessible areas are frequently the result of moisture extremes. Wet areas must be either drained or land-filled. Drainage (see drainage systems) is accomplished in several ways: by building a system of channels, by laying drainage pipes, and by pumping. In many cases embankments must be constructed to keep water out of the reclaimed areas. landfill operations require large quantities of suitable fill material such as sand, which is often obtained by dredging adjacent areas. Water is supplied to arid areas either by pumping it from underground sources or by transporting it through an irrigation system.

Reclamation of wetlands has significantly enhanced the well-being of several nations. The Netherlands is an outstanding example. Over a period of centuries the amount of arable land has been significantly increased by the construction of dikes, enclosing portions of the shallow coastal waters, which are then drained off. The Zuider Zee project, the first phase of which was a 29-km (18-mi) dike completed in 1932, has created nearly 200,000 ha (500,000 acres) of polders, which is land reclaimed from the sea. Because much of this land is below sea level, continuous pumping is required to maintain the desired water-table level.

Considerable areas in salt marshes have also been reclaimed in eastern England by constructing embankments that separate the marshes from the sea and draining the marshes both with ditches inside the embankments and through tidal sluices. Because the marshes are above sea level, pumping is not needed. Land reclaimed from the sea has such a high salt level that only salt-tolerant vegetation can be planted during the first few years. However, after several years, rain leaches out most of the sodium ions and soil conditions improve.

An example of large-scale reclamation of freshwater marshes is the drainage in the 1930s of the Pontine Marshes of Italy, a 75,000-ha (195,000-acre) region of dunes and marshes about 70 km (45 mi) southwest of Rome. The project not only opened new land for settlement and agriculture but also helped control malaria, a product of the marshes.

Reclamation of wetlands has been less actively pursued in the United States, because such areas are highly productive habitats for fish, shellfish, birds, and wildlife. Reclamation of arid lands, however, has been a major goal of the U.S. Bureau of Reclamation. The Lower Colorado River Project has transformed desert areas, such as the Imperial Valley of California, into some of the most productive cropland in the world.

The Dutch experience also points a warning, however. Although Dutch farmers have wrested some of the world's highest yields from their reclaimed lands, they have done so at considerable expense. The annual cost of drainage and dike repairs exceeds $400 million; runoff from fertilizers and pesticides adds to the burden of water pollution; the constant pumping has compressed polder soils, causing them to sink while, at the same time, it is feared that sea levels may be rising. In consequence, in 1993 the Netherlands government announced plans to reverse the reclamation process, returning over 240,000 ha (600,000 acres) to marsh, lake, and forest.

RECLAMATION OF ARTIFICIALLY CREATED WASTE AREAS

The major problems associated with waste areas that are the result of human activityÑindustry, mining, and waste disposalÑare slope instability, chemical leachates, and soil nutrient deficiencies. Such waste areas occupy only a small fraction of the land area, but they are frequently concentrated in highly populated regions and, in addition to their ugliness, often cause air and water pollution over widespread areas. In such cases the need for reclamation is particularly pressing; but when it is accomplished, it results in healthier environments as well as useful land. Slope instability can be reduced by reshaping the waste areas into landforms with gentler slopes that will conform with the surrounding landscape features. Erosion is prevented through water-control measures and the establishment of a vegetative cover.

The Aberfan disaster in Wales in 1966Ñin which 170 people, mostly schoolchildren, were killed when a coal-refuse bank collapsedÑresulted in one of the largest reclamation projects of derelict land. The piles of black wastes that were formerly so common in many of the urban areas of England and Wales have been transformed into landscaped parks and preserves. Because of their proximity to heavily populated areas, costs have been high, but large numbers of people have benefited from the vastly improved environment.

Many disused mine-waste piles dot the landscapes of the older coal-mining regions of the United States, particularly in the East. Although most cause serious environmental problems, few have been reclaimed.

Reclamation of Surface-Mined Land

Of much greater magnitude in terms of the amount of land involved are the scars left by surface-mining operations, especially where coal has been mined. Federal and state laws now require the reclamation of land disturbed by strip-mining operations, and a concerted effort is underway to reclaim land disturbed in past operations. Most commonly mine operators are required to restore the land to a use at least as good as that which existed prior to mining. This restoration may involve stockpiling the upper soil layers, segregating and burying potentially toxic material, reshaping the piles to approximately the original contour, respreading the soil, and establishing a vegetative cover. Such reclamation is most efficiently done as part of the mining operation. Reclamation of old abandoned surface mines is more difficult and more costly.

Reclamation of surface-mined areas in the western United States and Canada is even more difficult because of the arid climate and, in some cases, high elevations. Nevertheless, surface mining will probably expand rapidly there in the next few decades, not only for coal but also for oil shale and oil sands.

Reclamation of Chemically Polluted Land

Methods used in alleviating problems of chemical pollution vary, depending upon the nature of the chemicals involved. High concentrations of soluble salts can be reduced by leaching the salts from the surface layers of the soil with water. Acidity can be lessened by applying calcium-containing material, such as pulverized limestone, to the soil. The improvement may be only temporary, however. Mine wastes often contain large quantities of pyrite (FeSM), which reacts with oxygen and water to form sulfuric acid and other toxic products. Acid is thus continuously produced, and a continuing need exists for periodic treatment following the initial reclamation.

The chemical and physical properties of the waste are sometimes so adverse to plant growth that the only satisfactory reclamation measure is to cover the waste with a thick layer of soil material. In other cases it may be possible to improve conditions by applying another waste material, such as the fuel ash produced by coal-burning electric-generating stations or sewage sludge from municipal treatment plants.

Landfill Reclamation

The most common reclamation problem throughout the world involves the disposal of urban wastes. Although most such wastes are inert or biodegradable and seldom contain hazardous toxic materials, they can constitute public-health problems. Many attempts have been made to reclaim valuable materials from the waste and to produce energy or new products from it; nevertheless, most of it is still disposed of on land. Ideally, such disposal sites are isolated from surface and subsurface waters, the wastes are compacted and covered with soil, and a vegetative cover is established. Unfortunately, there is a shortage of suitable sites, especially near large cities (see waste disposal systems).

In addition to urban wastes, reclamation problems are created by highway and reservoir embankments, pulverized fuel ash, and wastes resulting from the removal and processing of such materials as sand and gravel, building stone, limestone, bauxite, china clay, iron ore, gold, and a variety of heavy metals.

Reclamation usually involves the establishment of vegetation. Selection of species and strains that are tolerant of adverse conditions can reduce site-modification costs and improve the chances for success. Where possible, time-tested methods of site preparation and plant establishment are used. For example, success is more likely if lime and fertilizer are incorporated into the upper layers, a seedbed is prepared, seed is drilled into the soil, and a mulch is applied.