Dredging

Dredging is an excavation activity or operation usually carried out at least partly underwater, in shallow seas or fresh water areas with the purpose of gathering up bottom sediments and disposing of them at a different location. This technique is often used to keep waterways navigable.

It is also used as a way to replenish sand on some public beaches, where sand has been lost because of coastal erosion. Dredging is also used as a technique for fishing for certain species of edible clams and crabs, see fishing dredge.

A dredger (or “dredge” as is the general usage in the Americas) is any device, machine, or vessel that is used to excavate and remove material from the bottom of a body of water. For example, a scoop attached to the end of a rope or pole by which a man can draw sediments up from the bottom of a pond is a dredger. Developing this idea further, a motorized crane equipped with a drag bucket or clamshell (grabber) that is used to scoop material from the bottom of a body of water is also a dredger. The crane could be located on the bank, or perhaps mounted on a barge. If the crane is mounted on a barge, the entire vessel is referred to as a dredger.

The process of dredging creates spoils (excess material), which are carried away from the dredged area. Dredging can produce materials for land reclamation or other purposes (usually construction-related), and has also historically played a significant role in gold mining. Dredging can create disturbance in aquatic ecosystems, often with adverse impacts.

The Panama Canal (Spanish: Canal de Panamá) is a 48-mile (77.1 km) ship canal in Panama that connects the Atlantic Ocean (via the Caribbean Sea) to the Pacific Ocean. The canal cuts across the Isthmus of Panama and is a key conduit for international maritime trade. There are locks at each end to lift ships up to Gatun Lake (85 feet (26 m) above sea-level). The Gatun Lake was used to reduce the amount of work required for a sea-level connection. The current locks are 110 feet (33.5 m) wide. A third, wider lane of locks is being built.

France began work on the canal in 1881, but had to stop because of engineering problems and high mortality due to disease. The United States (US) later took over the project and took a decade to complete the canal in 1914, enabling ships to avoid the lengthy Cape Horn route around the southernmost tip of South America (via the Drake Passage) or to navigate the Strait of Magellan. One of the largest and most difficult engineering projects ever undertaken, the Panama Canal shortcut made it possible for ships to travel between the Atlantic and Pacific Oceans in half the time previously required. The shorter, faster, safer route to the US West Coast and to nations in and along the Pacific Ocean allowed those places to become more integrated with the world economy.

During this time, ownership of the territory that is now the Panama Canal was first Colombian, then French, and then American; the United States completed the construction. The canal was taken over in 1999 by the Panamanian government, as long planned. Annual traffic has risen from about 1,000 ships when the canal opened in 1914, to 14,702 vessels in 2008, the latter measuring a total of 309.6 million Panama Canal/Universal Measurement System (PC/UMS) tons. By 2008, more than 815,000 vessels had passed through the canal, many of them much larger than the original planners could have envisioned; the largest ships that can transit the canal today are called Panamax. The American Society of Civil Engineers has named the Panama Canal one of the seven wonders of the modern world.