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| Titel |
Sediment accumulation and net storage determined by field observation and numerical modelling for an extensive tropical floodplain: Beni River, Bolivian Llanos |
| VerfasserIn |
Arved Schwendel, Rolf Aalto, Andrew Nicholas |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250095971
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| Publikation (Nr.) |
 EGU/EGU2014-11450.pdf |
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| Zusammenfassung |
| Lowland floodplains in subsiding basins form major depocentres responsible for the storage
and cycling of large quantities of fine sediment and associated nutrients and contaminants.
Obtaining reliable estimates of sediment storage in such environments is problematic due to
the high degree of spatial and temporal variability exhibited by overbank sediment
accumulation rates, combined with the logistical difficulties inherent in sampling locations far
away from the channel. Further complexity is added by the high channel mobility,
which recycles sediment and reconfigures the relationships between channel and
floodplain morphology, sediment transport and overbank sedimentation. Estimates of
floodplain accretion can be derived using a range of numerical sedimentation models
of varying complexity. However, data required for model calibration are rarely
available for the vast floodplains associated with tropical rivers. We present results
from a study of channel-floodplain sediment exchange fluxes on the Rio Beni, a
highly dynamic, tropical sand-bed tributary of the Amazon in northern Bolivia. The
Beni transports high concentrations of suspended sediment, generated in the river’s
Andean headwaters, and disperses this material across an extensive floodplain wetland
that experiences annual inundation over an area of up to 40000km2. We utilise
estimates of overbank sedimentation rates over the past century derived from 210Pb
analysis of floodplain sediment cores collected along a 375km length of channel,
including sampling a range of channel-floodplain configurations within the channel
belt and on the distal floodplain (up to 60km from the channel). These data are
used to investigate spatial and temporal variations in rates of floodplain sediment
accumulation for a range of grain sizes. Specifically, we examine relationships between
sedimentation rate and distance from the channel, and characterise within channel belt
variability in sedimentation linked to patterns of channel migration and associated
levee reworking. Field data are used to inform a hydrodynamically-driven model of
overbank sedimentation and to derive uncertainty-bounded estimates of total floodplain
sediment accumulation. Sediment exchange due to planform channel mobility is
quantified using a numerical model of meander migration, calibrated using analysis of
remote sensing imagery to determine rates and geometry of channel migration. Our
combined data and model analysis allows the construction of a mean annual sediment
budget for the Beni, which suggests channel-sediment exchange fluxes in the order of
100Mta-1, equivalent to 10% of the sediment load of the mainstem Amazon. |
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