Driftcretions: The legacy impacts of driftwood on shoreline morphology

Abstract

This research demonstrates how vegetation interacts with physical processes to govern landscape development. We quantify and describe interactions among driftwood, sedimentation, and vegetation for Great Slave Lake, which is used as proxy for shoreline dynamics and landforms before deforestation and wood removal along major waterways. We introduce driftcretion to describe large, persistent concentrations of driftwood that interact with vegetation and sedimentation to influence shoreline evolution. We report the volume and distribution of driftwood along shorelines, the morphological impacts of driftwood delivery throughout the Holocene, and rates of driftwood accretion. Driftcretions facilitate the formation of complex, diverse morphologies that increase biological productivity and organic carbon capture and buffer against erosion. Driftcretions should be common on shorelines receiving a large wood supply and with processes which store wood permanently. We encourage others to work in these depositional zones to understand the physical and biological impacts of large wood export from river basins.

The pulse of driftwood export from a very large forested river basin over multiple time scales, Slave River, Canada

“…We placed a wood event at 1933 because a historic photo shows wood in transport during this date. We chose 1954 because this was a high water year, coupled with evidence from the Great Slave Lake that large amounts of drift piles germinated in the early 1950s [ Kramer and Wohl , ]. We chose 1960 because this was the first year of high flows after 5 years of a decreasing pattern of flows similar to the pattern preceding 2011 (see section 4.4).…”

“…Correspondence between different lines of evidence for “return interval” of wood floods on the Slave River suggests that periodicity in wood flux is real and not an artifact of a particular data set or method of analysis. Succession of driftwood deposits from large wood floods like 2011 are a primary driver of outer deltaic morphology and vegetative patterns in the Slave River Delta [ Kramer and Wohl , ]. Tree core dates on trees growing on drift piles suggest that discrete driftwood berms are deposited every 30–50 years [ Kramer and Wohl , ], which corresponds fairly closely with the wood flood recurrence interval of ∼27 years from the log raft.…”

“…Furthermore, vegetated drift piles identified by Kramer and Wohl [] were clumped around the 1930s, early 1950s, mid‐1960s, late 1970s, and early 1990s. These dates correspond well with evidence from the Pelican Islands, log raft, and historic photos.…”

“…Most of the wood transported through the Slave River is sourced from the banks of the Peace River and deposited along the shores of Great Slave Lake [ Kindle , ], where the wood interacts with sediments and vegetation to create complex shoreline morphologies [ Kramer and Wohl , ]. In a write‐up of a field excursion in 1917, Kindle [] writes “there is probably no lake in North America which receives anything like the amount of driftwood which is poured into the Great Slave Lake, chiefly through the Slave River” (p. 358).…”

Logjams are not jammed: measurements of log motions in Big Creek, Idaho

“…Logjam studies have been conducted in steep, single-threaded mountainous settings [Wohl and Beckman, 2014] and low-gradient alluvial settings where wood-floodplain interactions are important [Wohl, 2013;Collins et al, 2012]. Logjams which grow to a size such that they span the entire channel width and are of significant length are referred to as 'log rafts' -these features can occur in low-gradient alluvial settings [Boivin et al, 2015], behind reservoir dams [Moulin and Piégay, 2004;Le Lay and Moulin, 2007;Fremier et al, 2010] and along coastlines [Kramer and Wohl, 2015]. To date, no studies have explored large, channel-spanning 'log rafts' in steep, mountainous, single-threaded reaches.…”