Ports and Harbors (Water Science)

Peoples of ancient civilizations often built their cities on the shores of natural harbors. A harbor is place on the coastline that is protected from the full effects of tide and currents (a steady flow of ocean waters in a prevailing direction). Harbors are often shaped like horseshoes. They are surrounded by land with a narrow opening through which ships can pass. Man-made harbors use structures such as walls or barriers built into the water to protect anchored ships from tide or storm damage.

Building cities near harbors permitted the construction of ports for trade. A port is a place on a shoreline for the loading and unloading of cargo from shipping vessels. Ports can be located on the ocean coast or on the shores of lakes and rivers. Cities with working ports are also called seaports or port cities.

Many of the great cities of the ancient world were seaports. Seaports allowed cities to grow and flourish. Trade made them wealthy. Ports also sheltered ships of war, sometimes a necessity to guard desirable seaports from invasion. The ancient seaport of Alexandria (Egypt), located along a man-made harbor along the Mediterranean Sea and the end of the Nile River, thrived for centuries. Alexandria was invaded several times and ruled by the Egyptians, Greeks, and Romans. The modern city of Alexandria, Egypt, is located a few miles (kilometers) from the underwater ruins of the ancient seaport.

Modern ports and harbors

Improvements in technology has allowed ships to travel faster, carry more cargo, and load with greater ease. Ports have grown in size to accommodate today’s bigger, faster ships. However, many parts of modern ports closely resemble their ancient counterparts.

In modern day, there are over 185 seaports in the United States. Trade with other nations, called overseas trade, is important to a nation’s economy. Two types of overseas trade occur, imports and exports. Imports are goods and materials that are shipped into United States from other countries. Exports are goods and materials from the United States that are shipped to other nations. Ships move most U.S. overseas trade, and shipping on waterways remains one of the least expensive means of transporting goods.

Modern ports have several special structures that help with the movement of cargo between land and ships. Navigation channels or ship channels that ships travel into port are marked "roadways." Docks and piers permit vessels to moor (secure to the dock) and for cargo to be loaded and unloaded from ships. Cranes and ramps aid the movement of cargo. On land, ports have large warehouses to store cargo. The waterside port area is connected to inland transportation systems such as roads, railways, pipelines, and airports. This allows cargo from ships to be loaded onto trucks, trains, or airplanes for transport to inland destinations. Cargo is often stored in containers that can be loaded from trucks to trains to ships. For example, metal boxes on railroad cars can be detached and loaded directly onto barges or ships. Liquid cargo, such as oil or gasoline, can be piped from large reservoirs onboard ships into tanker trucks or tanker train cars.

Building and maintaining successful ports

Modern ports must be built to accommodate several types of ships, from oil tankers and tugboats, to barges and passenger ships. Ports not only aid trade; they are also important centers of travel for people. Passenger ferries and cruise ships carry people from one port to another. Ports usually have separate docks, piers, and places to moor for passenger vessels.

Even if a port is located in a natural harbor, river, or lake, the waterways must be maintained. Ship channels must be kept sufficiently deep to permit the passage of ships, barges, and tugboats. Dredging makes waterways deeper by removing the silt (tiny particles of rock, soil, and plant material) and mud that clogs channels. Docks, piers, and jetties (protective rock barriers) need continual maintenance. The U.S. government and local port authorities oversee daily operations at United States ports.

Problems, concerns, and the future of ports

Ports are vital to the economies of the cities in which they are located. However, the warehouses, docks, cranes, and shipyards of a working port are generally not considered attractive. Ports occupy large amounts of land near waterways. Commercial ships, vessels used for trade, are large and difficult to navigate. They can pose a danger to small recreational boats. Laws often prohibit or limit recreational boats in ship channels and other key port waters. Thus, ports can sometimes restrict individuals’ use of shorelines, coastal areas, and waterways. City planners work to carefully balance the needs of the port with the interests of citizens and businesses.

The Port of Hong Kong

A junk, a form of boat popular in the waters, sails into the port of Honk Kong, China.

A junk, a form of boat popular in the waters, sails into the port of Honk Kong, China.

Hong Kong, China, is one of the major ports of the world. A large natural harbor with deep waters and several barrier islands (narrow coastal island parallel to the mainland) protect the city of Hong Kong from the tides. The port serves commercial, military, and passenger vessels. During the year 2001, nearly 40,000 seagoing vessels used Hong Kong’s port.

(In the nineteenth century, Great Britain took control of Hong Kong. In 1898, a treaty with China gave Great Britain control of Hong Kong for 99 years. On July 1, 1997, the treaty expired and Hong Kong reverted to Chinese control.)

Over the past century, Hong Kong grew into one of the wealthiest most productive ports in the world. When the port was established, it had a sparse population and no industry. In modern day Hong Kong is a major industrial center and one of the most densely populated cities in the world. Hong Kong must import raw materials for construction and manufacturing. However, the city prospers because of its factories that produce clothing, shoes, toys, electronics, plastics, and jewelry for export to other countries.

Ports also pose special challenges for marine (ocean) and coastal environments. The constant presence of large vessel traffic can disturb plants, animals, and microorganisms that live in port and harbor waters. The construction of jetties and breakwaters changes the effect of tides and currents within a harbor or port area. This alters the water chemistry of water within the jetties. Water chemistry is the balance of temperature, minerals, salts, and even pollutants in water. Even a slight change in the temperature, muddiness, or salinity (saltiness) of water can harm marine life.

As ships require fuel to operate, port areas have to store and transport large amounts of gas and oil. Leaks, spills, and shipwrecks damage underwater and coastal habitats. Ports also increase the amount of other types of pollutants, such as litter. However, ships produce less air pollution than airplanes, trucks, or trains loaded with the same tonnage of cargo.

Transportation systems are always changing and improving. Ships, trains, and airplanes are becoming bigger, faster, and more efficient. Trucks and airplanes, only invented a century ago, are already essential means of moving goods and materials. Yet a port, an idea centuries old, remains an efficient link for land and ocean transport.


Barrier Island: Long, narrow coastal island built up parallel to the mainland.

Export: Raw materials or goods that are shipped, traded, or sold to other nations.

Import: Raw materials or goods that are produced in a foreign country and brought into another.

Jetty: Structure built out into the sea, a lake, or a river to protect the harbor or shore against waves or tides.

Navigation channel: Passage in a waterway that is naturally deep or dredged to permit the passage of ships, or a defined, well-marked passage that leads from the docks to open waters; also called ship channel.

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