ABSTRACT
Much of the previous discussion on the characteristics of rivers was related to rivers in their “natural” state. It is important to know the characteristics of natural or free-flowing rivers so that we can better manage and protect them. Also, as will be discussed in later chapters, much of the work done today is in the restoration of river systems. The National Research Council in its 1992 report, “Restoration of aquatic ecosystems” (NRC 2002), defined restoration as the “return of an ecosystem to a close approximation of its condition prior to disturbance.” In order to do so, some knowledge of the undisturbed characteristics of river systems is required so we know what to restore the system to. However, by far the majority of rivers today are regulated or controlled to some degree. Freeflowing, or undisturbed, rivers are relatively rare. According to the World Wildlife Federation, in 1986 (WWF 1986) only 18% of the rivers in North America longer than 1000 km were free-flowing, including (length in parentheses) the Mackenzie (5472 km), Athabasca (1231 km), Liard (1115 km), Yellowstone (1080 km), Fraser (1370 km), and Kuskokwim (1050 km).
