Environmental Engineering Reference
In-Depth Information
3 Regulated Rivers
3.1 INTRODUCTION
Much of the previous discussion on the characteristics of rivers was related to rivers in their “natu-
ral” state. It is important to know the characteristics of natural or free-lowing 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), deined 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. Free-
lowing, 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-lowing,
including (length in parentheses) the Mackenzie (5472 km), Athabasca (1231 km), Liard (1115 km),
Yellowstone (1080 km), Fraser (1370 km), and Kuskokwim (1050 km).
Since the majority of our river systems are controlled or regulated, it is important to have a fun-
damental understanding of those regulatory or control structures in order to determine their impact
on the river's physical, chemical, and biological characteristics. The two primary sources of control
or regulation are:
Flow modiication structures, such as dams and weirs
Channel modiication such as the dredging and straightening of rivers
The practice of river regulation using these sources of control has been around for thousands of
years. The concept of “harnessing” and “controlling” rivers was the early goal of river management
and river engineering, as expressed by Benjamin Franklin:
Rivers are ungovernable things, especially in hilly countries. Canals are quiet and very manageable …
Benjamin Franklin 1772
Channelization and control were the early common goals of engineering projects in Europe and
elsewhere. For example, in 1817, the German engineer Colonel Johann Gottfried Tulla initiated
channelization of the braided Alsatian section of the Rhine, and he is often quoted as stating, “as a
rule, no stream or river needs more than one bed.” By the 1900s, virtually all of the major rivers in
Europe had been channelized.
Most of the early efforts were directed toward small rivers or sections of rivers. It was not until
the last two centuries, and notably the last century, that complete control of rivers was commonly
achieved, due in large part to advances in dam-building technology. The 1940s to the 1980s was
the construction era of water resource management in the United States (Wurbs and James 2002).
The period from 1950 to 1980 included the peak of dam building worldwide and during that period
in North America over 200 large dams (over 15 m high) were constructed per year. While in more
recent years the rate of construction of large dams has decreased dramatically, large dams have
and are being constructed, such as the Three Gorges Dam in China, which became fully opera-
tional in 2012. Plans for even larger dams, such as in the Congo, are being considered.
 
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