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Courtice, Gregory James

University of British Columbia

The temporary release of suspended sediment in lotic environments is a common phenomenon that can result from construction activities in rivers. Aquatic ecosystems may be harmed by exposure to fine sediments. Temporary suspended sediment releases are described by the variables of suspended sediment concentration (SSC; mg∙L⁻¹) and duration of exposure (DoE; h). Activities that induce temporary suspended sediment releases have fixed scopes of work that yield trade-offs between SSC versus DoE; managing an activity to reduce one variable will likely lead to an increase in the other. Predominant management policies prioritize reducing SSC, leading to increased activity durations (and project costs), however there is no framework to evaluate if this approach results in more desirable environmental outcomes. The objective of this thesis was to develop a framework to understand how SSC and DoE can be co-managed during temporary suspended sediment releases to improve both environmental and economic outcomes. Several steps were taken to achieve this objective. First, a common source of temporary suspended sediment releases (i.e., in-stream construction-induced suspended sediment) was characterized by exploring the abiotic and biotic factors that govern point-source suspended sediment releases and resulting adverse effects to ecosystems. Then, a categorical analysis was undertaken to reassess existing dose-response observation data for salmonids. Candidate variables of SSC, DoE, and their product, suspended sediment dose (SSD; mgh∙L⁻¹), were evaluated for their potential to explain major physiological and lethal effect outcomes. The categorical model was then adapted to quantify uncertainty and develop a management solution space, demonstrating that SSD represents mean salmonid dose-response dynamics well for a commonly used regulatory benchmark limit. The research demonstrates the value of using multilevel logistic regression to describe the categorical data structure of the dose-response dataset for salmonids. Graphical presentations of the management operating space revealed a conceptual framework for identifying improved environmental and economic exposure domains. Two practical case studies supported the theoretical conclusions. Achieving desirable project outcomes was found to require a clear operational definition to understand the necessary measurements and modeling so that management actions may be considered in terms of their costs against the costs associated with mitigation of opposing risks.

Text

2022-12-07

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/83372

Civil Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/