Doctoral Dissertations

Date of Award

5-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Geography

Major Professor

Carol P. Harden

Committee Members

Liem Tran, John Schwartz, Robert T. Pavlowsky

Abstract

Large woody debris (LWD) has become universally recognized as a key component of the ecological and geomorphological function of river systems. The use of LWD as a restoration tool in Midwestern river systems is widespread, yet LWD-related restoration strategies are primarily supported by research from the Pacific Northwest or other physiographically similar regions. The purpose of this dissertation research was to investigate the longitudinal arrangement patterns of LWD and to characterize LWD and its effects on sediment storage within the Big River, a Midwestern river system located in the Missouri Ozarks. I adopted a multi-scale approach to analyze (1) large-scale longitudinal patterns of LWD arrangement, (2) potential geomorphic and riparian control mechanisms of LWD arrangement, (3) reach-scale characteristics of LWD, and (4) reach-scale relationships between LWD and sediment storage.

The results of this research demonstrate that the longitudinal arrangement of LWD along the Big River is not random. Along many segments of the Big River, LWD density is spatially periodic. Periodicity showed a strong positive association with gravel bar spacing and meander wavelength, although there were insufficient data to statistically confirm the relationship. Furthermore, reaches that exhibited strong periodicity yielded stronger relationships between LWD density and the geomorphic/riparian independent variables tested. Analyses consistently identified valley width and sinuosity as being associated with LWD density.

Wood loads in the Big River were low relative to those in streams located in the commonly studied Pacific Northwest, and high relative to other low- to mid- gradient river systems. In general, wood piece size was large relative to those of other river systems, and may suggest, along with field observations, that bank erosion is the dominant wood recruitment mechanism. Furthermore, the contribution of LWD to reach-scale sediment storage was low relative to other in-channel sediment stores.

These results provide a baseline characterization of LWD for a semi-confined-meandering river system. This will help provide a directive for LWD-related management in stream restoration ventures in semi-confined meandering river systems and provide a first step toward developing more accurate models of LWD dynamics.

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