Canal

Canal is an artificial waterway dug across land. Canals have served as important means of transporting goods and water for thousands of years. Canals are usually used for shipping large quantities of goods when speed is not important. In such cases, canals are cheaper than such alternatives as railroads or trucks.

There are two major types of canals: navigation canals and water conveyance canals. Navigation canals link bodies of water, enabling vessels to travel between them. Water conveyance canals, which include irrigation canals and drainage canals, carry water from one place to another. Such canals are often referred to as aqueducts or irrigation structures. This article deals mainly with navigation canals.

Navigation canals may connect two bodies of water, such as two lakes, or a lake and a river. Navigation canals also link oceans with seaports that lie near, but not directly on, the oceans. In addition, many navigation canals are parts of canalized rivers. Canalized rivers have their navigable stretches connected by a series of dams and locks. These structures adjust for different water levels and help traffic avoid waterfalls, shallow areas, snags, and other navigation hazards. Such major inland waterways as the Mississippi and Ohio rivers in the United States and the Rhine and Seine rivers in Europe are canalized rivers.

Early canals were ditches. They measured about 3 to 5 feet (0.9 to 1.5 meters) deep and 15 to 40 feet (4.6 to 12 meters) wide. They were built for shallow barges towed by horses or mules. Through the years, boats and canals have become larger. The Panama Canal, first opened in 1914, was expanded in the early 2000’s. Its largest locks are 1,400 feet (430 meters) long and 180 feet (55 meters) wide, with a minimum water depth of 60 feet (18 meters).

Most navigation canals are built and operated by government agencies. The U.S. Army Corps of Engineers designs, builds, and maintains the navigation canals of the United States. These waterways are used by industry and by private citizens. But many water conveyance canals are privately owned. They are used by such agencies and businesses as irrigation districts and public utilities.

Planning and building a canal

When planning a canal, engineers study the terrain. They determine the course of a canal and decide whether it will need locks. The width and depth of a canal are based on the size of the vessels it will handle. Environmental specialists also consider how a canal will affect surrounding plant and animal life. For example, a canal might disrupt the migration of certain animals and alter their food supply. Water conveyance canals sometimes have crossover bridges to allow for animal migration. However, such bridges may be impractical for large ship navigation canals.

The construction of a canal primarily involves the digging and moving of earth and rock. Such materials as clay or crushed rock may be added to a canal to reduce leakage and prevent erosion. Some canals are lined with asphalt or concrete.

Canal locks

Canal locks are rectangular chambers that enable ships to move from one water level to another by varying the amount of water in the lock. Most locks are made of stone or concrete and have watertight gates at each end. Water flows in and out of locks by gravity. No pumps are needed. Locks do, however, require a supply of water at the upper level of the canal. As a result, some locks have special reservoirs and auxiliary canals to ensure an adequate water supply.

Locks are used to adjust for changes of elevation along the course of a canal and variations in tide level near a seacoast. To move a vessel upstream, where the water level is higher, the water level in the lock is lowered to that of the water just downstream. The downstream gates are opened. The ship then moves slowly into the lock. After the ship is tied down and secured, the gates close. Valves open to fill the lock with water from upstream. The flow of water is carefully controlled to prevent the ship from colliding with another vessel or from ramming the gates. As the lock fills, the ship rises to the level of the water upstream. The upstream gates open, and the ship passes through. To move a ship downstream, the process is reversed. After a ship enters the lock, the water is drained out. The ship is lowered to the downstream level.

Major canals of the world

The Panama and Suez canals

are the most important canals in the world. Both of them provide valuable navigation short cuts. Both have figured prominently in military affairs and international politics.

The Panama Canal links the Atlantic and Pacific oceans. It extends from Limón Bay on the Atlantic to the Bay of Panama on the Pacific. The total distance is about 51 miles (82 kilometers). The Panama Canal is the busiest canal in the world. More than 13,000 ships pass through it annually.

The Panama Canal reduces the sea route between New York City and San Francisco by more than 9,000 miles (14,400 kilometers). Without the canal, ships traveling between the two cities would have to pass around the southern tip of South America. The Panama Canal played a strategic role during World War II (1939-1945). It enabled United States naval forces to move quickly and easily between the Atlantic and Pacific oceans.

The Suez Canal extends for about 120 miles (193 kilometers), including entrance channels at both ends. The canal stretches between Port Said, Egypt, and the Gulf of Suez, an arm of the Red Sea. The Suez Canal allows ships to move directly between the Mediterranean and Red seas. It serves as a major water link between Europe and Asia. For example, the canal shortens sea voyages between the United Kingdom and India by about 5,000 miles (8,000 kilometers). Without the canal, ships traveling between the two countries would have to pass around the southern tip of Africa. The Suez Canal was blocked by sunken ships in 1967, during the Arab-Israeli war. Sea traffic between Asia and Europe was disrupted. Egypt reopened the canal in 1975.

Major canals in the United States and Canada

include the Soo Canals, the Chicago Sanitary and Ship Canal, and the All-American Canal. Canals also form an important part of the St. Lawrence Seaway and other major waterways.

The Soo Canals, on the United States-Canadian border, connect Lakes Superior and Huron. The Chicago Sanitary and Ship Canal enables ships to travel between Lake Michigan and the Mississippi River. The ships move via the Chicago, Des Plaines, and Illinois rivers. The All-American Waterway, in southern California, carries water from the Colorado River to the Imperial and Coachella valleys, important agricultural areas.

The St. Lawrence Seaway consists of a system of canals and locks, the St. Lawrence River, and several lakes. It links the Great Lakes and the Atlantic Ocean. The system extends for about 450 miles (724 kilometers) from the eastern end of Lake Erie to Montreal, Quebec. The seaway includes the Welland Ship Canal.

Major canals in other countries

include the Grand Canal in China and several canals in Russia and in Western Europe. The Grand Canal is a system of canals and navigable sections of rivers. It includes the Yangtze and Huai rivers and the Huang He (Yellow River). It extends about 1,000 miles (1,600 kilometers) through China. It is the world’s longest artificially created waterway.

In Russia, a system of canals links the Volga River with the Arctic Ocean, the Baltic Sea, the Don River, and Moscow. Major rivers in western Europe are also connected by many canals. They include the Amsterdam-Rhine Canal in the Netherlands and the Albert Canal and Brussels-Charleroi Canal in Belgium. The Kiel Canal in Germany connects the Baltic and the North seas. Germany’s Main-Danube canal links waterway systems between the North and Black seas.

History

People have built and used canals for thousands of years. The oldest canals were constructed in the fertile area between the Tigris and Euphrates rivers known as Mesopotamia. The earliest Mesopotamian canals date from around 4,000 B.C. The ancient Egyptians constructed a navigation canal around a waterfall on the Nile River before 2000 B.C. The Chinese began construction of the Grand Canal during the 500’s B.C. The ancient Greeks may have invented the lock, by which the water level is adjusted, as early as the 300’s B.C.

Important European canal systems were built in the 1100’s and 1200’s in the region that includes present-day Belgium and the Netherlands. The Canal du Midi, completed in 1681, became an important waterway in France. The Canal du Midi enabled ships to travel from the Mediterranean Sea at Sête to the Bay of Biscay. The ships moved by way of Toulouse and the Garonne River. Today, however, the canal’s size permits only small barge and tourist traffic.

The first ship canals in the United States were begun in 1793 on the Connecticut River in Massachusetts and between the Santee and Cooper Rivers in South Carolina. The Erie Canal in New York, completed in 1825, opened up the Great Lakes region to ships from the Atlantic Ocean. It also helped make New York City the nation’s financial center. In addition, the success of the Erie Canal led to a great burst of canal building in the country. During the 1830’s, however, railroads began to replace canals as a means of transporting goods. Goods could be moved faster by railroad than by canal. Nevertheless, canals still play an important role in shipping goods, especially in Belgium, the Netherlands, and other European countries. Today, tourism has brought increased traffic to canals that pass through scenic countryside.