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| Titel |
Floquet theory of river ecomorphodynamics |
| VerfasserIn |
Matteo Bertagni, Paolo Perona, Carlo Camporeale |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250150835
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| Publikation (Nr.) |
 EGU/EGU2017-15347.pdf |
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| Zusammenfassung |
| Most of world population lives close and depends on freshwaters and related ecosystems. As
dramatic consequence, 48% of all rivers worldwide are hydrologically altered. Although
mankind lives by and controls river systems since millennia, a complete physically-based
understanding of the links among the various processes involved still remains elusive. Three
fundamental aspects control the physical state of natural rivers: flow stochasticity,
sediment transport and vegetation dynamics. The present work tries to shed light on the
bonds among these processes, following a temporal flow for the river dynamics.
During a particularly extreme flood event any previous ecomorphological pattern is
erased by the flow. However, sediment transport triggers the formation of migrating
bedforms, called free bars. Through a nonlinear analysis, with center manifold
projection, a long analytical expression is obtained for the bars amplitude, thus
completely defining bars geometry in the parameters space. Once the formative
event is extinguished, the flow rate decreases and the recently formed bars can
partially emerge from water. At this point vegetation develops over the bare bars
depending on flow stochasticity. As a realistic model for the flow stochasticity the
compound Poisson process is considered. However, in order to make the computation
analytically feasible, the stochastic time series for the discharge is replaced with an
equivalent periodic one, obtained as a sequence of a typical average event of the
stochastic series. In this manner, the new periodic streamflow signal, preserves the same
statistical properties of its stochastic correspondent. The periodic equation for the
vegetation dynamics can thus be spatially solved through Floquet theory, gaining which
portion of the bar is asymptotically colonised by vegetation. In conclusion, this
is the first theoretical work linking the trend of the vegetated area with the flow
parameters, and confirming that high flow variability hardens vegetation growth. |
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