HR: 0830h
AN: H51D-1113    [PDF]
TI: A numerical landscape-evolution model that simulates river width dynamics and consequent geomorphological features (braided river dynamics, terrace formation, .)
AU: * Davy, P
EM: Philippe.Davy@univ-rennes1.fr
AF: Geosciences Rennes, Campus de Beaulieu, Rennes, 35042 France
AU: Castelltort, S
EM: Sebastien.Castelltort@univ-rennes1.fr
AF: Geosciences Rennes, Campus de Beaulieu, Rennes, 35042 France
AU: VandenDriessche, J
EM: Jean.Van-Den-Driessche@univ-rennes1.fr
AF: Geosciences Rennes, Campus de Beaulieu, Rennes, 35042 France
AB: We present a landscape evolution model that explicitly considered lateral stream erosion to simulate river width dynamics. The numerical code (_ros) is a walker-based method which solves the tectonic/erosion/deposition mass balance for a stochastic distribution of climatic events. The erosion flux is assumed to depend only on water flow and on topographic slope. According to the recent literature, we use the stream power-law model with threshold. The deposition flux is assumed to be proportional to suspended-sediment concentration; the proportionality factor is a sediment-transport distance $\xi$ whose value fixes the nature of mass balance equation: transport-limited if $\xi<<1$, detachment-limited if $\xi>>1$, and even any intermediate case. Lateral erosion is applied to domains (pixels) at the immediate vicinity of the walker route. As a first approximation, we assume that lateral erosion is proportional to basal erosion flux and to the height of river bank. _ros well reproduces the observed downslope widening of rivers. Clearly the river width is not a univocal function of discharge area as stated by most of the existing landscape evolution models; it has its own dynamics which mainly depends on erosion flux, and so on topographic disequilibrium. _ros also reproduces the classical river typology, braided, straight or sinuous, but not meandering whose physics is not yet included in the model (no dependency of lateral flux with river curvature). Braided rivers form during aggradation phases while a sinuous river mark the equilibrium stage. It is worth noting that lateral erosion favors river instability either in response to an external change of the hydraulic or tectonic conditions, or as a purely internal chaotic process. For instance autocyclic transitions between braided and sinuous shapes are observed in the simulations although no external parameter is modified. This instability is also responsible of terrace formations with also both deterministic causes (climatic or tectonic perturbations) and chaotic ones.
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 3220 Nonlinear dynamics
SC: Hydrology [H]
MN: 2003 Fall Meeting