Throughout history, major cities of the world have been on the shores of navigable waters - oceans, lakes and rivers. Although there is improved highway, rail and air transportation, good harbor facilities are still an important part of many city economies. Bulky freight such grain, coal and gravel is sometimes shipped most cheaply by barge on the 26,000 miles of improved inland waterways of United States.

Hydrologists help maintain navigable waters by providing information to engineers who study river currents and build physical and computer models to study sedimentation processes. These simulation experiments tell engineers where to place jetties and levees so as to minimize future silting problems.

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