Feedback between erosional morphology, sediment transport and abrasion in the transient adjustment of fluvial bedrock channels

This thesis explores the dependence of bedrock channel incision on coarse sediment supply through laboratory flume experiments and quantitative field observations of evolving channel morphology. Predictions of the saltation-abrasion model (Sklar and Dietrich, 2004) for sediment flux-dependent channel incision guide our efforts although the results are not model dependent. In channels where the dominant incision process is sediment abrasion, sediment transport and erosion are inherently coupled. Flume experiments support the form of sediment flux-dependent relations proposed in the saltation-abrasion model, but also suggest that the model is incomplete: channel bed morphology adjusts due to localized erosion, and bed morphology in turn influences local flow and sediment transport. The experiments document a positive feedback in which bedload is preferentially transported in local topographic lows due to lateral transport and abrasion in turn deepens those topographic lows. Under sediment-starved conditions this positive feedback results in the incision of narrow inner channels. In the Henry Mountains of southeast Utah, we monitored channel flow and resulting bedrock incision over 2.5 years in a human-perturbed bedrock channel where erosion had incised a narrow inner channel in which sediment transport and erosion were focused, similar to the flume experiments. In addition, the flow record shows that the maximum discharge flood was much less erosive than a lower but prolonged flood due to snowmelt flow. Large flash floods can be net depositors of coarse sediment in the channel, mantling the channel bed with coarse sediment and inhibiting erosion.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2007

Author dc:creator

• Johnson, Joel Peterson

Advisor dc:contributor.advisor

• Kelin X. Whipple.

• Earth, Atmospheric, and Planetary Sciences.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/42277

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/42277