Catastrophic flooding of the Mississippi
Rivers and
floodplains
Flooding Cedar Rapids, Iowa (2008)
The Amazon basin floods every year,
an integral part of this rainforest
ecosystem. Opposite the city of
Manaus, the Amazon and Negro
Rivers flow together. The Amazon is
muddy brown in contrast to the
clearer, dark waters of the Negro.
(Top) NASA image (June 29 2009).
Floods on the Negro receded;
flooding still evident along the
Amazon (image blurred by clouds).
(Bottom) Amazon and Negro rivers
(June 7, 2004), a year when seasonal
flooding was not extreme.
Tiny white flecks along the river are
buildings. The rainforest that lines the
river is dark green, while cleared land
is lighter in color. It is quite likely that
the flood actually extended across the
entire land between the two rivers, but
the dense forest canopy rises above
the water, hiding the floods beneath.
Rivers are dynamic
features in the landscape!
The wooden steamer, the SS Sultana, was
a Mississippi paddlewheeler built in 1863
and destroyed in an explosion in 1865
resulting in the greatest maritime disaster
in U.S. history. Some 1,800 passengers
were killed when one of the ship’s boilers
exploded near Memphis, Tennessee.
The Sultana on fire, from Harpers Weekly
The ship was originally built for the lower Mississippi cotton trade and had a legal
capacity of 376 passengers. When it sank, it had more than 2,000 people on board,
mostly Union prisoners of war released from their Confederate prison camps and on
their way home (many were from Ohio).
In 1982, an expedition uncovered the wreckage of the Sultana. Blackened
wooden deck planks and timbers were found about 32 feet under a
soybean field on the Arkansas side, about four miles from Memphis. The
Mississippi River has changed course several times since the disaster.
The main channel now flows about two miles east of its 1865 position.
Restoration of streams also involves the floodplain; not only because
the river flows sideways but also because the channel naturally migrates
and creates storage. Where and when possible, “let the river be a river”.
Bottom line
• Although there are general paradigms, no two rivers and streams
are alike.
– Even within one river system, habitat is extremely diverse and
dynamic.
• Rivers flow from upstream to downstream, but they also flow
sideways.
• The watershed is critical scale for management and research.
Both require a multidisciplinary approach.
• The majority of rivers and streams in the developed world have
been ditched, diked, dredged and/or dammed.
• River floodplains are important because they
– cover large areas of earth’s surface,
– contain highly adapted fauna and flora,
– interact closely with adjacent ecosystems (and the atmosphere),
– are under rising pressure from development, and
– provide “free” ecosystem services.
Seasonally inundated bottomland
forest communities along a stretch
of the Mississippi.
Seasonally inundated floodplain
forest along Amazon River. Note
white and black water stretches
(True-color Terra MODIS image;
September 8, 2002).
Sampling equipment
Surber sampler
Seine
Flow measurement
Kick seine
Fig 4-2. Moss
Stream order nomenclature
Stream order nomenclature (see also Fig. 11.7)
River Continuum
Concept
(Vannote et al. 1980)
Hypothesis:
The biology of a
stream is adapted to
gradients in physical
(geomorphological)
features of the
stream
Fig 4-11. Moss
Osborne, 2000
Hypothesis: The biology
of a stream is adapted to
gradients in physical
(geomorphological)
features of the stream
River Continuum Concept.
Fig 2 Vannote et al. 1980
The flood pulse
concept (Junk 1989):
The flood pulse is the
driving variable of the
river-floodplain
system. Biotic and
abiotic processes in
the Aquatic-Terrestrial
Transition Zone (ATTZ)
regulate species
composition, food
webs and nutrient
dynamics.
Várzea forest during dry phase
Inundated Várzea forest
The flood pulse concept (Junk 1989) states that the flood
pulse is the driving variable of the river-floodplain system
and that biotic and abiotic processes in the AquaticTerrestrial Transition Zone (ATTZ) are primary regulators of
species composition, food webs and nutrient dynamics.
Echinochloa polystachya
(creeping river grass)
Very fast growth rates.
Annual net production
among highest for all plants.
Important food source for grazers such as
capybaras, manatees, turtles, herbivorous fish.
Echinochloa polystachya.
Well adapted to unstable environment. Stands of this grass are
replaced by forests if flooding
becomes less and by aquatic
macrophytes if aquatic phase
dominates .
• Organisms must survive
during both wet and dry phases
 lots of survival strategies
(incl. migration, dormancy, seed
and rhizome production, etc.)
• High mortality (aquaticterrestrial pulse is high stress)
 strong pressure on organisms
to have short life cycles, rapid
reproduction, high reproductive
rates  high productivity.
• Nutrient release from
sediments under anoxic
conditions during aquatic phase.
• Anoxia in water and sediment
during flood periods  CH4 (and
H2S) production  pulsed
floodplains sources of
greenhouse gases.
The impact of the flood pulse on the fishes in the
floodplains of large Amazonian rivers (Junk 1996)
Ferreira C S et al. AoB Plants 2010;2010