Short-term response of a mountain stream to a sediment pulse and a major flood

Fojtik, Alexander Christian

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https://hdl.handle.net/2142/108416 Copy

Description

Title

Short-term response of a mountain stream to a sediment pulse and a major flood

Author(s)

Fojtik, Alexander Christian

Issue Date

2020-06-08

Director of Research (if dissertation) or Advisor (if thesis)

Cienciala, Piotr

Department of Study

Geography & Geographic InfoSci

Discipline

Geography

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

fluvial geomorphology, remote sensing, dam removal, sediment pulse

Abstract

Sediment pulses in river systems can result in massive inputs of sediment compared to background transport rate. Large floods, on the other hand, temporarily bolster a river’s sediment transport ability. Both phenomena occurred in the Sullivan Creek watershed of northeastern Washington within the span of a few months. The removal of the Mill Pond dam (a ~17 m tall impoundment dam) generated a sediment pulse, and was shortly followed by a large freshet flood, with a return interval estimated to be between 10 and 50 years. To understand the nature of the stream’s response to these events, I took advantage of two close-range remote sensing techniques, terrestrial LiDAR (TLS) and Structure-from-Motion (SfM). Data collected during two subsequent summers enabled me to map two reaches of Sullivan Creek and detect and track morphological change that took place between the surveys. I also carried out a comparative analysis of the capabilities of both techniques and assessed their compatibility for data fusion. Although other studies have successfully conducted fusion of these data types, the characteristics of the study site presented various challenges that complicate both data collection and quality. I found that, because of the presence of high canopy, extensive vegetation, and wood, TLS exhibits superior performance over SfM in the subaerial environment, by generating accurate “bare earth” topography. SfM can, on the other hand, generate bathymetric data, critical for the understanding of bed changes within the wetted channel. I found that, like other studies of sediment pulses, the channel bed reacted by fining substantially. However, even though I detected some substantial channel changes, the study stream did not experience massive aggradation or transformation of reach-scale morphology to the degree reported in many other channels subject to sediment pulses, including cases of other dam removals. Similarly, the extent of channel erosion in Sullivan Creek was much less than what would be expected given the magnitude of the freshet flood. These findings may provide insight into the morphological adjustments generated by future dam removals, especially under extreme flow conditions.

Graduation Semester

2020-08

Type of Resource

Thesis

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Copyright 2020 Alexander Fojtik

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