Dredging

Building and maintaining our underwater highways

Historically, water transportation was the key to exploration of uncharted territories. As settlement progressed, roads, railways, and eventually airways were added to become our modern, global transportation system. The man-made or maintained parts of this system are our nation's transportation infrastructure: roads, railroads, airports, locks, dams, ports, and navigation channels.

The water transportation system, operating since the early 1800s, has played a major role in the growth of the United States' economy. Today this system serves as the pillar to one of the most extensive and economically significant waterborne commerce operations in the world.

Economic Theory of Adam Smith, Water Transportation, and the Potential to Grow

The classical economist Adam Smith recognized the efficiency of water transportation in 1776, when he published his revolutionary book, An Inquiry into the Nature and Causes of the Wealth of Nations. Smith championed water over ground transportation when he analyzed why some nations are better off than others.

Smith stated:

"A broad wheeled wagon, attended by two men and drawn by eight horses, in about six weeks time carries and brings back between London and Edinburgh near four ton weight of goods. In about the same time, a ship navigated by six to eight men, and sailing between the ports of London and Leith, frequently carries and brings back two hundred ton weight of goods.

"Six or eight men, therefore, by the help of water-carriage, can carry and bring back in the same time the same quantity of goods between London and Edinburgh as fifty broad-wheeled wagons, attended by a hundred men, drawn by four hundred horses."

As a result of this comparison, Adam Smith came to a simple but important conclusion: "Countries are only wealthy when they have growth potential." This unprecedented concept was echoed in our Constitution, which empowered the United States government to form economic incentives. These incentives stimulated commerce, building the basis for the nation's economic development.

Modern Economics of Shipping

Today, wagons and 200-ton cargo ships are of times past, but we can look at modern vessels and compare their capacity efficiencies. Modern technology allows the building and operation of ever larger vessels. Worldwide automation, standardization, and advanced technology applications have made water transportation safer and ever more efficient.

Approximately 95 percent of all United States international trade moves through our ports. Our new global economy must allow for fast and efficient transportation of goods meeting consumer needs and providing the means for import and export opportunities. As world populations increase, demand for goods will also increase, requiring further expansion of our water transportation system. As global economic forces exert pressure, we must build bigger and more efficient ships, and navigation channels must be deepened and widened. The designing, building, and maintaining of these channels can be compared to building an underwater highway. The huge vessels of the future entering and exiting our harbors will need underwater super highways.

Efficiency in Size

Evolution of ships: From the time of the two-masted schooner to today's super container giants, seagoing vessels not only have increased carrying capacity but are also wider, longer, and faster and require deeper channels. Improving "productivity" of shipping means more cargo moved faster, safer, and more efficiently while consuming less energy and producing less pollution.

Evolution of shipping: From moving goods in barrels, baskets, and sea chests to the container-ship concept implemented in the 1960s was a long process. Containerization operates under the premise that durable and nondurable goods can be safely and economically shipped worldwide in standardized 20-ft-long containers (called twenty-foot equivalent units - TEUs). These containers are intermodal, can be stowed efficiently on container ships, and can be placed easily on railroad cars, in aircraft cargo holds, or on semitrailer trucks for door-to-door delivery. Other shipping methods include break/bulk, super colliers, and tankers.

Over time, container ship design evolved into a standard limited to a size able to pass through the Panama Canal. Today's container ships, however, can be more than 1,000 feet long, carry up to 6,000 TEUs, and require at least 45-foot channel depth. Ships of the future will be bigger yet and will need navigation channels at least 50 feet deep. Other nations in Europe and Asia are improving shipping channels to accommodate vessels with 60-foot drafts and deeper.

• Coastal & Hydraulics Laboratory