Why do port authorities need to dredge?
A. Over 90 percent of the nation’s top 50 ports in foreign waterborne commerce require regular maintenance dredging. Together these ports move nearly 99 percent of U.S. overseas trade by weight and 61 percent by value. Many deep draft seaports in the United States are located at the mouths of rivers where upstream runoff collects sediments which are carried down river and deposited on harbor bottoms. Most ports are not naturally deep harbors; they are man-made through a process of dredging and landfilling. In parts of New York harbor, for example, the navigation channels are naturally only 18 feet deep, while sections of the Mississippi are only 6 feet deep. Today’s modern ships can require drafts of up to 45 or 50 feet. Sediment also has to be removed to provide turning basins for ships and adequate water depth along waterside facilities. Without routine dredging, areas of navigation channels could change from 40 to 35 feet in one year. Such a dramatic change would prohibit many ships
