Doctoral Dissertations

Date of Award

5-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Civil Engineering

Major Professor

Athanasios N. Papanicolaou

Committee Members

Vasilios Alexiades, John S. Schwartz, Daniel C. Yoder, Murugesu Sivapalan

Abstract

Anthropogenic activities in intensively managed landscapes (IMLs) have significantly modified material travel times and delivery, and have led to more pronounced event-based dynamics compared to undisturbed conditions. Understanding and mitigating human impacts requires the use of both field-based observations and physically-based numerical models to tease out causal relationships and feedbacks between the relevant processes across the cascade of scales, from the plot to the watershed. Unfortunately, there are no event-based numerical models capable of adequately simulating sediment fluxes across scales in IMLs, thus hampering our ability to understand and mitigate anthropogenic impacts.The goal of this study was to develop a conceptual modeling framework for IMLs that considered all the connections and interactions between terrestrial and in-stream sources on an event basis, and to use the framework to identify a characteristic scale unit (CSU) representative of sediment flux laws within the drainage network. The CSU was considered to be a scale at which local-scale variability in landscape properties ceased to have an effect on mean trends in sediment fluxes and, thus, an appropriate scale for simulating/monitoring sediment fluxes for watershed management purposes.The framework was developed and tested in the South Amana sub-watershed (SASW), IA. An upland erosion model was coupled with an instream sediment transport model to simulate material fluxes along different pathways in SASW. A sediment fingerprinting model was also utilized to constrain the predicted contributions of terrestrial and instream sources. Modeling advances made included the incorporation of a surface roughness evolution threshold, space/time variant flow resistance representations of landscape attributes, and the stochastic representation of material origins, travel times, and delivery to the watershed outlet. The developed model was validated via an extensive field campaign performed at scales ranging from the plot to the sub-watershed.The study results revealed thresholds of influence of landscape roughness attributes, and highlighted important intra-seasonal trends in source contributions driven by the co-play of land use and rainfall. A CSU for sediment fluxes and the factors affecting it were identified. Future studies must examine the CSU as dictated by the interplay between event-based and seasonal dynamics, and the implications for watershed management.

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