Shape of a River - Geomorphology
A river's shape is determined over time through
the continuous interaction between water and the
landscape. Rivers and streams of all shapes and
sizes have a tendency toward dynamic equilibrium,
where the energy of the system is expressed in its
pattern, dimension and profile.
While the largest floods move large amounts of
sediment over short periods of time and shape the
valleys and floodplain, they are relatively rare.
Research over the past 50 to 60 years has
increasingly demonstrated the importance of
bankfull flows in defining a river's shape.
The term bankfull refers to the water
level stage that just begins to spill out of the
channel into the floodplain. Bankfull flows tend to
occur fairly frequently, on the average every two
out of three years. Because bankfull floods occur
frequently, they move the most sediment over time
and shape the stream channel itself. The range of
forces-from major floodplain-forming events to
recurring bankfull flows-are necessary for healthy