Human interventions have altered almost all the river systems of
the world. These interventions include channelization,
alteration of stream courses, construction of levees, building of
drainage channels, construction of dams and locks, installation
of river training works, flow diversions, changes in land use,
and many more. River systems respond to such changes through
changes in flow, stages, gradients, or sediment supplies and
through attempts to attain a new dynamic equilibrium suitable to
the changed conditions. However, the time frame for obtaining a
new dynamic equilibrium in response to an altered regimen ranges
from a few years to decades or more. There are numerous examples
of such alterations of large river basins and of the consequent
responses of the rivers. In almost, all cases, the intervention
is associated with a changed regimen of sediment delivery. The
amount of sediment that is delivered either increases as a result
of changed land use or decreases as a result of the construction
of some form of sediment retention devices. Such devices may be
created by an act of nature or intentionally, such as in the case
of the construction of locks and dams. This paper presents three
brief case studies, one each for the Kankakee, Mississippi, and
Illinois River basins in the midwestern part of the United States
of America. The drainage areas for these river basins at the
locations where the case studies were conducted are 1920 square
miles, 118,900 square miles, and 14,200 square miles,
respectively. The impacts of channelization are illustrated by
the case study of the Kankakee River, and the impacts of lock and
dam construction for commercial navigational purposes are
illustrated by the case studies of the Mississippi and the
Illinois Rivers.
