Earth and Planetary Sciences ETDs

Publication Date

1-30-2013

Abstract

Much of the current literature on ancient fluvial systems is based on studies of modern rivers, but fails to differentiate between degradational and aggradational systems. That is a problem because degradational systems are not preserved and therefore are not representative of fluvial systems found in the rock record. Current research is attempting to rectify this shortcoming by exploring distributive fluvial systems (DFS) in active sedimentary basins, which have the highest likelihood of being preserved. DFS are sediment deposits that occur when rivers exit the confinement of mountain valleys and become laterally mobile in broad sedimentary basins. They are characterized by a radial pattern of channels from an apex of channel networks. The main mechanisms through which channel networks on DFS evolve are bifurcation and avulsion. Instabilities in river channels that lead to bifurcation and avulsion are related to the 1) slope of the river channel, 2) the slope of the ground perpendicular to the channel, and 3) the ratio of the slope of the floodplain or valley perpendicular to the channel-belt, relative to the down-stream or down–valley slope of the existing channel (Mackey and Bridge, 1995; Jones and Schumm, 1999; and Karssenberg and Bridge, 2008). This study sought to find a correlation between bifurcation and slope on large (>30 km) braided DFS by measuring long-profile slopes, cross-profile slopes, and slope ratios along active distributive channels. Using digital elevation models and Landsat images, a database of 1,253 long-profile slope values, 1,245 cross-profile values, and 1,112 slope ratios along 98 large DFS was compiled to gain a better understanding of slope relationships along large braided DFS and to determine if there is a correlation between bifurcation and slope. This study found a high statistically significant difference between slope ratios of non-bifurcating and bifurcating areas. Non-bifurcating areas were also found to have shallower gradients than bifurcating areas. Cross-profile slope is greater for non-bifurcating areas in proximal regions of the DFS and greater for bifurcating areas in the medial regions, indicating a change from avulsion-dominated channel migration to bifurcation-dominated migration across these regions. Further work needs to be carried out to look at the role incision plays on slope ratios on DFS, particularly in proximal regions. Additionally, a small number of long-profile slopes had positive values. More research is needed to determine what is causing these positive slope values and to what extent they interfere with the study of the relationship between slope and bifurcation.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Meyer, Grant

Project Sponsors

NSF CI 0753336 "CI-TEAM Implementation Project: Advancing Cyberinfrastructure-based Science through Education, Training, and Mentoring of Science Communities"; NASA NNS04AB25G "Center for Rapid Environmental Assessment and Terrain Evaluation (CREATE) Research Studies"; and by the Department of Earth and Planetary Sciences

Language

English

Keywords

slope, bifurcation, distributive fluvial system, DFS

Document Type

Thesis

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