Modeling Floodplain Depositional Patterns under Variable Flood Regimes
Abstract
One of the more difficult aspects of predicting riverine fluxes to the ocean is intermediate storage in lowland floodplains. This storage is significant: floodplain deposition maintains and builds up low-lying lands along rivers and on deltas. Especially in deltas it is one of the processes that counteracts sea-level rise and maintains stability of the deltaic coast. AquaTellUs is a 3D floodplain architecture model that uses a nested model approach; a 2D longitudinal profile, embedded as a dynamical flow path in a 3D grid-based space. We model the main channel belt as a 2D longitudinal profile that responds dynamically to changes in channel profile geometry, water discharge, sediment load, grain-size distribution and sea level based on first-order, physics-based principles. Sediment flux is described with a modified Exner equation by separate erosion and sedimentation components. Erosion flux along the main flowpath depends on river discharge and channel slope, and is independent of grain-size. Depositional flux along the channel path as well as in the lateral direction into the floodplain depends on the local stream velocity, and on grain-dependent settling rates. Lateral depositional patterns are informed by analysis of remote-sensing imagery of recent flood deposits and by comparison to SRTM and ASTER GDEM2 elevation data of floodplain topography. Floodplain deposition is an event-driven system — only peak discharge events cause overbank flow, crevasse-splays, and potential channel avulsion. The computational architecture of AquaTellUs preserves stratigraphy by event, allowing for preservation of flood layers of variable thickness and composition. We here present depositional cross-sections and pseudo-wells resulting from numerical experiments that show the pronounced effect of different probability density functions for river discharge and sediment load, i.e. flooding recurrence times on the resulting floodplain aggradation. AquaTelllUs distinctly shows a more exponential geometry of elevated channel belts under highly variable flood regimes, with potential implications for breach dynamics. In addition, the model predicts that natural levee complexes are distinctly higher near the apex of delta plains and the levee heights taper off towards the coastal plain.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMEP34A..01O
- Keywords:
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- 0545 COMPUTATIONAL GEOPHYSICS / Modeling;
- 1616 GLOBAL CHANGE / Climate variability;
- 1820 HYDROLOGY / Floodplain dynamics;
- 1856 HYDROLOGY / River channels