Figure 1.3. Sinuosity vs. slope with constant discharge.
Changes in sediment and water discharge at a particular point or reach in a stream may have
an effect ranging from some distance upstream to a point downstream where the hydraulic and
geometric conditions will have absorbed the change. Thus, it is necessary to consider a
channel reach as part of a complete drainage system. Artificial controls that could benefit the
reach may, in fact, cause problems in the system as a whole. For example, flood control
structures can cause downstream flood damage to be greater at reduced flows if the average
hydrologic regime is changed so that the channel dimensions are actually reduced. Also,
where major tributaries exert a significant influence on the main channel by introducing large
quantities of sediment, upstream control on the main channel may allow the tributary to
intermittently dominate the system with deleterious results. If discharges in the main channel
are reduced, sediments from the tributary that previously were eroded will no longer be carried
away and serious aggradation with accompanying flood problems may arise.
An insight into the direction of change, the magnitude of change, and the time involved to
reach a new equilibrium can be gained by:
Studying the river in a natural condition
Having knowledge of the sediment and water discharge
Predicting the effects and magnitude of future human activities
Applying knowledge of geology, soils, hydrology, and hydraulics of alluvial rivers
The current interest in ecology and the environment have made people aware of the many
problems that humans can cause. Prior to this interest in environmental impacts, very few
people interested in rivers ever considered the long-term changes that were possible. It is
imperative that anyone working with rivers, either with localized areas or entire systems, have
an understanding of the many factors involved, and of the potential for change existing in the
river system.
1.8
Previous Page
