HARBOUR

also spelled Harbor, any part of a body of water that is sufficiently sheltered from wind, waves, and currents to be used by vessels for safe anchorage or the discharge and loading of cargo or passengers. A harbour is distinguished from a port in that a harbour does not necessarily have facilities for the transfer of cargo that a port always has. The most important aspect of a harbour is the amount of shelter it provides. Some, such as the harbours of New York City and San Francisco, are naturally sheltered from the open sea by narrow straits and land barriers. Many harbours, however, have open sides, called exposures, that permit wind and waves to blow in from the exposed directions. Barriers built to protect exposed harbours are called breakwaters, which consist of an exterior protective layer of large stone or concrete boulders or of interlocking armour plates and an interior filled with rubble and small rocks. On some open coasts, such as Madras, India, harbours have literally been created by building breakwaters. An equally important criterion is the depth of the harbour. The size of modern ships requires that harbours have designated ship routes, or channels, sometimes with depths in excess of 30 m (100 feet). Since few natural harbours have such depths, periodic channel dredging is needed. For many years the main piece of dredging equipment was the bucket-ladder dredge, which is a vessel that temporarily moored itself at the dredging site and dropped a ladder with a belt of continuously moving scoops to the desired depth. The scoops brought up material from the bottom and dumped it over the top of the ladder into a chute. Newer suction dredges pull bottom silt along with water into hoppers where the silt settles and the water runs off. Dredged silt is either taken out to sea and dumped or used as landfill in reclamation projects ashore. Most harbours are charted according to what is called a controlling depth, which indicates the shallowest areas that may be encountered. Ships are directed along the channels by colour-coded floating buoys, which may also be used to alert ships to the presence of navigation obstructions like shallow water, rocks, and submerged wrecks. Inside a harbour, ships may be deployed in a number of ways. Some harbours have areas for anchorage only, where ships drop anchor at a distance from other docking facilities. These areas must have what is called holding ground, a bottom in which a ship's anchor can be embedded well enough to hold the ship against the pull of wind or current. Most docking facilities are used for the transfer of cargo and are built in a variety of ways. Concrete gravity walls, filled with earth from behind, rely on sheer weight for stability. This can be enhanced by sinking deep foundations with concrete monoliths or precast caissons. Piers built on piles of timber, reinforced concrete, or steel that have been driven deep into the bottom are called piled jetties and exhibit great durability. A more recent development is the sheet-piled quay, which is a seawall made of deeply corrugated steel sheets that interlock together and provide great strength. The great shipping ports are lined with cargo piers and related facilities. The combined shorelines of New York Harbor are more than 773 km (480 miles) long, but this distance is increased by about 240 km if the berthing piers of the port are included. Besides traditional docks, some harbours provide for the bulk transfer of petroleum from giant tankers, which need large amounts of space and bottom clearance. Bulk terminals are set offshore from other port activity, and only a light pier is needed to carry a pipeline to them. Among other facilities found in major ports are dry docks, which are enclosed locks that can be emptied of water so that repairs can be made to the hulls of ships. Harbours have played an important role in civilization for as long as people have gone to sea in boats. Throughout history, great cities have risen to power based on their ability to utilize their access to the sea. The Phoenicians built artificial harbours at the cities of Sidon and Tyre in the 13th century BC. A large harbour stood at the entrance to ancient Alexandria and was marked by Ptolemy's famous lighthouse, Pharos. The Mediterranean harbours of the ancient Greeks and Romans were also vital to their empires. Most harbours are natural, and although there are examples of artificial-harbour construction dating back thousands of years, the vast majority were neither altered nor improved upon until the mid-1800s. Early ships were small, and the natural harbours of the world were adequate. With the growth of trade and commerce that accompanied the Industrial Revolution, however, ships also grew in size, necessitating the enlargement and deepening of harbours by artificial means. Modern harbours range from small enclosures crowded with pleasure craft to commercial ports covering thousands of acres.