HR: 14:40h
AN: H53D-05    [Abstracts]
TI: Experimental investigation on the formation of alluvial cut terraces
AU: * Meunier, p
EM: meunier@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, Laboratoire de dynamique des systemes geologiques Boite 89, 4 place Jussieu, PARIS, 75252 France
AU: Metivier, f
EM: metivier@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, Laboratoire de dynamique des systemes geologiques Boite 89, 4 place Jussieu, PARIS, 75252 France
AU: Guises, r
EM: guises@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, Laboratoire de dynamique des systemes geologiques Boite 89, 4 place Jussieu, PARIS, 75252 France
AB: In order to better understand the formation of alluvial terraces, experiments were conducted on a micro scale experiment. 22 braid plains (with varying control parameters such as input water, bedload and initial slope), were reproduced and their evolution in time monitored. In each case boundary conditions remained constant during each experiment and were set so the system is initially in a disequilibrium state that favors erosion of the braid plain. These experiments reveal that, as the system relaxes towards equilibrium, incision and terrace abandonment occurs in a complex manner. In several cases the rivers homogeneously and continuously cuts into its bed leaving only one paired terrace. In other cases the systems apparently destabilizes and successions of asynchronous phases of widening and incisions are observed. Series of terraces both paired and unpaired are abandoned. Analysis of mass transport and of the topographic evolution of the network enables to define two relevant parameters: the space occupation ratio corresponds to the hypsometric integral of the braid plain, whereas the effective stream power index defines the ratio of excess stream power to bedload input. A threshold of effective stream power is then shown to exist below which continuous incision occurs and above which autogenic cycles of terrace formation develop.
DE: 4558 Sediment transport
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting