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JANUARY 25, 2021
JANUARY 25, 2021
conditions: low flow, snow present on floodplain
Site summary
swift-moving channels characterized by a series of pools, riffles, and scattered gravel bars
LB: roughly meter-tall, near-vertical banks comprised of fine sediment that show evidence of recent erosion
RB: large, low gravel bar
significant evidence of historic and recent beaver activity
hydroelectric dam located just downstream
Top left: Mountain Whitefish present in a pool within the reach.
Bottom left: Rounded clasts are present on gravel bar.
Right: West-facing view looking downstream taken from the tail-end of a gravel bar. Two flows converge here to form form a main flow that is actively scouring the right bank. A low-angle gravel bar dominates the left bank, with some flow-rafted wood present.
Above: Not the world's finest field sketch.
Geomorphic units: Gravel bars, beaver-made structures, pools, riffles, etc
Processes: Bank erosion (resulting in lateral movement of the channel), fine sediment deposition resulting from beaver-made structures, bar formation behind the larger beaver structure
Above: East-facing view of the reach taken from a submerged gravel bar between two main flows. The difference in color, caused by the presence /absence of algae, serves as an effective indicator for relative flow velocities at this location. An abandoned beaver dam is present in the background.
Eroding Banks
Banks comprised of mostly fine sediment
Rapidly and actively eroding
Thoughts: Banks of fine sediment suggest historic slackwater conditions. This condition is not present in this reach today. Consequently, the free-flowing channel is now actively eroding into these banks. In many areas, the erosion seems to have the most lateral extent nearest to the bed. Large blocks of the bank also appear in the channel. This suggests that the banks are eroding through a calving process.
Evidence of Beavers
Evidence of old and new beaver activity
Thoughts: In the future, beaver may be successful in damming one of the channels to a greater extent than what is currently present. Evidence for a more robust historic structure is present, but it has not been maintained to be able to pond water despite evidence of newly-incorporated materials.
Additional Site Notes
Third Dam (the third impoundment on the Logan River) is just downstream from this reach, which I believe caused the historic slackwater conditions. At some point, the crest height of the dam must have been changed, causing incision through the former reservoir deposits. A recent article said that plans to "dredge" the former reservoir sediment may come to pass in the next few years, dependent on funding.
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