The characteristics of inland navigation and the purpose of various types of improvements to river navigation are described briefly. A newly implemented performance monitoring system of data collection is explained in some detail. How the operation of waterways influences the design of future improvements is also described.

• THE inland navigation system of the United States consists of apJ? rOximately 25,000 miles (40 000 km) of navigable channels, 15,000 miles (24 000 km) of which are 9 ft (2. 7 m) or more in depth. The Mississippi River and its tributaries constitute the majority of this system (Figure lL About 1,800 firms use tl1ese waters as a means of livelihood, and they transport more than 560 million tons (494 million metric tons) of commerce by shallow draft vessels throughout the United States each year. The average distance shipped by water has increased 20-fold over the past 40 years; the maximum tow size has increased from 5,000 tons (4500 metric tons)/tow to approximately 50,000 tons (45 000 metric tons)/tow.