Coevolution of hydrodynamics, vegetation and channel evolution in wetlands of a semi-arid floodplain
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2015-04
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EGU General Assembly 2015
Resumen
The Macquarie Marshes are located in the semi-arid region in north western NSW, Australia, and constitute part
of the northern Murray–Darling Basin. The Marshes are comprised of a system of permanent and semi-permanent
marshes, swamps and lagoons interconnected by braided channels. The wetland complex serves as nesting place
and habitat for many species of water birds, fish, frogs and crustaceans, and portions of the Marshes was listed as
internationally important under the Ramsar Convention.
Some of the wetlands have undergone degradation over the last four decades, which has been attributed to
changes in flow management upstream of the marshes. Among the many characteristics that make this wetland
system unique is the occurrence of channel breakdown and channel avulsion, which are associated with decline
of river flow in the downstream direction typical of dryland streams. Decrease in river flow can lead to sediment
deposition, decrease in channel capacity, vegetative invasion of the channel, overbank flows, and ultimately result
in channel breakdown and changes in marsh formation. A similar process on established marshes may also lead to
channel avulsion and marsh abandonment, with the subsequent invasion of terrestrial vegetation. All the previous
geomorphological evolution processes have an effect on the established ecosystem, which will produce feedbacks
on the hydrodynamics of the system and affect the geomorphology in return.
In order to simulate the complex dynamics of the marshes we have developed an ecogeomorphological
modelling framework that combines hydrodynamic, vegetation and channel evolution modules and in this presentation
we provide an update on the status of the model. The hydrodynamic simulation provides spatially distributed
values of inundation extent, duration, depth and recurrence to drive a vegetation model based on species preference
to hydraulic conditions. It also provides velocities and shear stresses to assess geomorphological changes. Regular
updates of stream network, floodplain surface elevations and vegetation coverage provide feedbacks to the
hydrodynamic model.
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Palabras clave
Hydrodinamic, vegetal and channel evolution, Wetlands, Semi-arid floodplain, Macquarie Marshes