Separation of the stream and floodplain (by the
construction of levees, for example) denies
organisms such as fish, amphibians, and reptiles
access to backwaters and floodplain lakes-spawning
areas for some species, feeding areas for others,
slow-current refuges for still others. A floodplain
provides storage for floodwaters. By constraining
the channel, rivers will reach higher stages,
exacerbating flooding downstream.
Construction of levees tends to lower the water
table adjacent to the river. Lower water tables can
stress existing vegetation and reduce the potential
for regeneration. Levees increase stream energy
within the channel, which increases streambed
erosion and destabilizes banks. The overall effect
is impaired water quality, decreased productivity,
degraded habitats and loss of biodiversity
and Ambrose, 2003).
Without periodic flooding, river bottom forests
will degrade. Nutrient and energy cycles (in both
floodplain and river) will be disrupted due to lack
of exchange between river channel and floodplain.
The floodplain is usually a net importer of
dissolved inorganic material and a net exporter of
particulate organic matter (Ward
and Stanford, 1995). The diversity of species,
ages and successional
stages of floodplain forests depends on
seasonal fluxes of water.