Rates and Mechanisms of Coastal Erosion in the Bay of Fundy

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Coastal erosion associated with rising sea levels and increased storminess threatens infrastructure in Canada and around the globe. Models of risk are evolving to incorporate the episodic nature of coastal erosion, but these efforts to establish firmer, evidence-based definitions of risk require frequent, high-resolution surveys of the coast, which until recently have been costly and logistically difficult. The emergence of Structure-from-Motion (SfM) technology, however, enables rapid, low-cost, accurate surveys of the coast, which is opening new avenues for investigation of episodic erosion. SfM constructs 3-D surfaces from overlapping photographs. The name comes from the ability of SfM to use images collected by a moving camera with positions that are unknown at the time of image capture. This ability has enabled the use of unmanned aerial vehicles (UAVs) for collection of photographs for SfM reconstruction of coastal morphology. The use of UAVs to conduct low-cost repetitive coastal surveys with SfM forms the core of the measurement approach in the proposed research. The specific focus of the research is on rates and mechanisms of coastal erosion in the Minas Basin of the Bay of Fundy, Canada. Two projects will measure cliff erosion rates and the factors that control them, and another will examine rates and mechanisms of sediment storage and removal from side channels during periods of low and high stream discharge. Cliff erosion in the Minas Basin threatens infrastructure, but it also determines the ecologically important sediment texture of the seabed. A recent study in my group showed that cliff retreat rates over the past 20 years are almost 50% larger than during the previous 30 years. I plan to employ frequent UAV-based SfM surveys, combined with measurements of rainfall, wind, and water level to investigate the underlying causes of observed increases in the rate of coastal retreat. Suspended sediment concentration in the Minas Basin affects habitat in the water column by influencing the light field. Sediment concentration increases fivefold in the winter for reasons that are under investigation. One potential source of sediment to the Basin is erosion of mud from side channels during periods of high stream discharge. It is difficult to estimate volumes of sediment released during high discharge events with conventional methods, because the muds in side channels are dangerous to traverse. I plan to use UAV-based SfM surveys of the Belmont River in Nova Scotia to constrain conditions under which significant erosion and infilling occur in side channels and to constrain the volume of sediment involved. Canada is faced with accelerating rates of coastal erosion. The proposed research will benefit Canada by developing and implementing new strategies for low-cost surveying of coastal morphology that are essential to building informed understanding of the rates and mechanisms of coastal change.