Combining GPR and historical aerial photographs to investigate river channel morphodynamics, Oldman River, southern Alberta

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Labey, Katie
St. Pierre, Heather
Sundsten, Jennifer
Seaman, Oliver
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Lethbridge Undergraduate Research Journal
River channels are dynamic landforms that play an important role in regulating riparian ecosystems. At a fundamental level, river erosion and deposition produce changes in the riparian zone that lead to the creation of new habitat or reworking of existing habitat. Despite considerable riparian research along the Oldman River in southern Alberta, little is known about historical channel dynamics and the resulting implications for riparian habitat. This research paper documents long term dynamics of a segment of the Oldman River at Fort Macleod, AB. Specifically, historical aerial photographs and a ground penetrating radar (GPR) were used to reconstruct how the river channel and bar features evolved over the last 70 years. Results from the aerial photographs indicate that the channel has undergone pronounced changes since 1938, with a trend of increasing meander curvature and decreasing wavelength. Channel bank reinforcement at Fort Macleod will likely constrict further meander development and force continued downstream meander migration. Subsurface imaging of a channel bar with GPR reveals a dominant mode of vertical accretion by bedload deposition at high flow stages, indicating a compound feature formed by overlapping unit bars. Observations of other bars along the Oldman River indicate similar modes of emplacement. Overall, results from this case study provide important context for assessing recent changes in riparian habitat. Application of this approach to other river segments will be of value in assessing whether similar patterns of channel and bar dynamics exist throughout the Oldman watershed.
(Alta.) -- Channelization , Riparian ecology -- Alberta -- Oldman River Basin