Modified and traditionally unstable channels eventually undergo a process of adjustment
to reach stability. Channel adjustments might include such changes as aggradation,
degradation, bend migration, and bar formation. These channel adjustments are often
predictable.
 Where modified channels are over widened, shear stress decreases and deposition occurs.
Where modified channels are over-deepened, large flows are contained within the channel
and begin to undercut banks.
The graphic below shows a typical channel evolution following modification for
agricultural drainage.
Through a process of downcutting, bank erosion, and redeposition in the channel, a new
bankfull capacity channel and active floodplain are formed at a lower elevation. The
original floodplain has been abandoned and is now termed a terrace.
Deposition and erosion processes within some low-gradient and straightened channels
eventually lead to pool-riffle and meander formation.
(Adapted from Brookes and Sear 1996; and
Thompson 1986)
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