HR: 1340h
AN: H43A-0367    [Abstracts]
TI: Geometric Properties of Bifurcating Delta Distributary Channels
AU: * Edmonds, D A
EM: dedmonds@geosc.psu.edu
AF: Department of Geosciences, The Pennsylvania State University, 513 Deike Building, State College, PA 16802
AU: Slingerland, R L
EM: sling@geosc.psu.edu
AF: Department of Geosciences, The Pennsylvania State University, 513 Deike Building, State College, PA 16802
AU: DeSibour, R M
EM: rmd193@psu.edu
AF: Department of Geosciences, The Pennsylvania State University, 513 Deike Building, State College, PA 16802
AB: The process of channel bifurcation lies at the heart of delta function and form, yet the geometries and stabilities of distributary diffluences, and the hydrodynamic conditions that give rise to them, cannot be predicted. To better understand this process we have collected the distributary network topologies of 26 deltas representing a broad range of climates, sediment and vegetation types, and river discharges. Channel widths, channel lengths from diffluence to diffluence, diffluence angle ($\alpha$), and the length-width ratio of diffluence pairs were measured from Landsat 5 images with 30 meter per pixel resolution using GIS tools. This resolution precluded channels narrower than 100 m; we also eliminated distributary channels that rejoined downstream. Diffluence order is here defined as the number of diffluences upstream of the current diffluence. Channel width was non-dimensionalized by width of 0$^{th}$ order channel and channel length was non-dimensionalized by the width of that channel. Results show that the distributary channel diffluence angles in our dataset are normally distributed with $\bar${$\alpha$} = 78$\deg$ and $\sigma$ = 26$\deg$ (N = 540). Channel widths and lengths are log normally distributed with $\bar{x}$ = 0.40 (N = 340) and 21.50 (N = 195), respectively. The channel width and length ratios of the bifurcate arms are square root-log normally distributed with $\bar{x}$ = 0.60:1 (N = 170) and 0.57:1 (N = 68), respectively. A statistically significant positive correlation (R$^2$ = 0.57; N = 195) exists between dimensional channel length (L) and width (W) of bifurcates such that $L = 13.33W$^{1.08}$, consistent with scaling theory. Partitioning of these properties within a delta was examined by binning the data according to diffluence order. When binned and averaged by diffluence order, diffluence angles show no trend, however there is a well-defined decrease in channel width, channel length with increasing order. Channel width and length ratios show the same trend, but are more scattered. When dimensional channel width and length are binned by order and fitted to a power law, length becomes a progressively higher order function of width with increasing diffluence order. A rational theory explaining these values remains to be proven. The diffluence angle is not easily predicted by the dynamics of turbulent plane jets, and the average width and length ratios of the bifurcate arms are opposite the ratios predicted by the theory of Bolla Pittaluga et al. (2003) for braid-bar diffluences.
DE: 4558 Sediment transport
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting