HR: 0800h
AN: H41D-0773    [Abstracts]
TI: Non linear bend instability theory and finite amplitude evolution of bed deformations in meandering rivers
AU: * Bolla Pittaluga, M
EM: miki@diam.unige.it
AF: University of Genova, Via Montallegro 1, 16145, Ge 16145, Italy
AU: Nobile, G
EM: gp@diam.unige.it
AF: University of Genova, Via Montallegro 1, 16145, Ge 16145, Italy
AU: Seminara, G
EM: sem@diam.unige.it
AF: University of Genova, Via Montallegro 1, 16145, Ge 16145, Italy
AB: We develop a three dimensional non linear asymptotic theory for flow and bed topography in meandering channels able to describe finite amplitude perturbations of bottom topography. The model extends a previous analysis on the equilibrium finite bed deformations, accounting here for arbitrary, yet slow, variations of channel curvature. This approach then allows us to formulate a non-linear bend instability theory, which predicts several characteristic features of the actual meandering process and extends results obtained by classical linear bend theories. In agreement with previous weakly non linear findings and consistently with field observations, the bend growth rate turns out to have a peak at some value of the meander wavenumber, typically larger than the resonant value of linear stability theory. Moreover, a feature typical of non linear waves arises: the selected wavenumber depends on the amplitude of the initial perturbation and, in particular, larger wavelengths are associated with larger amplitudes. The picture offered by results obtained through the present theory seems fully satisfactory and consistent with field observations as well as previous theoretical findings. Further substantiation of the model has been achieved by comparing predictions obtained for a test case (a reach of the Cecina river, Italy) with field observations. Finally the model is also extended to follow the evolution of bed deformations in time in order to investigate the morphological response of the river to a sequence of flood events characterized by a slow temporal variation of flow and sediment supply. Such an investigation would possibly provide a rational interpretation of the as yet loosely defined notion of formative discharge of an alluvial river.
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 1804 Catchment
DE: 1825 Geomorphology: fluvial (1625)
DE: 1826 Geomorphology: hillslope (1625)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting