Dryland avulsion sequences

Dryland avulsion sequences: Insights from data-model comparison of a terminal dryland river system

Karamitopoulos, P. (TU Delft Hydraulic Structures and Flood Risk)
Donselaar, M.E. (TU Delft Applied Geology; Katholieke Universiteit Leuven)
Weltje, G. J. (Katholieke Universiteit Leuven)
van Toorenenburg, K. A. (Shell International Exploration and Production BV)

2022

An advection–diffusion model of fluvial processes was used to analyze the stratigraphic expression of avulsions in terminal river systems and understand their control on basin-fill architecture. The initial and boundary conditions of the model runs (i.e., catchment area, smoothed initial topographic surface, grain-size distribution and sediment supply rates) were extracted from the modern Rio Colorado dryland terminal river system in the Altiplano Basin (Bolivia). Water-discharge and sediment-load values were derived from global regression curves and the BQART equation, respectively. To evaluate the robustness of the simulations, the model was tested under increasing sediment-load scenarios ranging from 0.003 m³/s to 0.095 m³/s. Data-model comparison provided insights into the role of avulsions in the geomorphological evolution of terminal river systems. The observed stacking of sediments, as captured by geospatial and geochronological data from the Rio Colorado, is consistent with the high sediment-load scenarios, which start with a single-thread fluvial channel that in time radially expands over the floodplain by successive river avulsions on account of alluvial-ridge aggradation and channel-floor elevation above the surrounding floodplain. The model output shows a laterally extensive, convex-upwards lobate topography which is in agreement with the lateral and longitudinal geomorphology in the upper and lower coastal plain of the Rio Colorado. The simulated inter-avulsion period, which is the time period between two successive full (or stabilized) avulsions in the model, varies from 0.18 to 1.2 kyr and is consistent with the OSL-age determination in the Rio Colorado with inter-avulsion periods up to 1.28 ± 0.34 kyr.

Compensational stacking
Dryland river system
Fluvial geomorphology
Inter-avulsion period
Numerical simulation
River avulsion

http://resolver.tudelft.nl/uuid:40de9698-1561-4c15-bb4f-f6d8a6c9e3a1

https://doi.org/10.1016/j.sedgeo.2022.106169

0037-0738

Sedimentary Geology, 436

Institutional Repository

journal article

© 2022 P. Karamitopoulos, M.E. Donselaar, G. J. Weltje, K. A. van Toorenenburg