The present-day shape, form, and surficial features, and the
future directional movement and changes of the morphometry of any
large river ecosystem and its interface zones are the results of
all the natural and human interventions on the system for the last
several decades to centuries. Almost all watersheds of all major
rivers of the world have already been subjected to intense
pressures from agriculture, urban sprawl, water supplies,
transportation, and recreation. Two of the major rivers of the
United States have also experienced these major constraints, and
they have responded with changes in their morphometry and riverine
environments. Specific examples are Pool 19 of the Mississippi
River, which extends about 74 kilometers (km), and the Peoria Lake
on the Illinois River, which extends about 16 km. Both of these
river reaches have been altered by the construction of locks and
dams and also serve as the sinks and transient conduits for the
sediments and other solid matters produced on and delivered from
their altered watersheds. The present-day Pool 19 was created
when a lock and dam were constructed in 1913 on the Mississippi
River near Keokuk, Iowa. Since then, this pool has lost about 68%
of its 1903 capacity, with annual sediment deposition of 3.3
million metric tons. Consequently, the lower portion of this pool
has been undergoing a transformation from a riverine to a
lacustrine to a palustrine and then to a terrestrial environment.
Research has shown that this transition may be final by the years
2030 to 2050. Both hydrologic and man-made activities are
responsible for this change. On the other hand, the fate of
Peoria Lake in the Illinois River is much more ominous: the
conversion from riverine to lacustrine, palustrine, and then
terrestrial environments may take place even more quickly. Many
other large rivers of the world may well face similar fates as a
result of past and ongoing hydraulic, hydrologic, and human
activities. This paper demonstrates this premise through a series
of examples, citing research conducted over the last several
decades.
