Athabasca River Avulsion Underway in the Peace‐Athabasca Delta, Canada

Abstract

Avulsions change river courses and transport water and sediment to new channels impacting infrastructure, floodplain evolution, and ecosystems. Abrupt avulsion events (occurring over days to weeks) are potentially catastrophic to society and thus receive more attention than slow avulsions, which develop over decades to centuries and can be challenging to identify. Here, we examine gradual channel changes of the Peace-Athabasca River Delta (PAD), Canada using in situ measurements and 37 years of Landsat satellite imagery. A developing avulsion of the Athabasca River is apparent along the Embarras River-Mamawi Creek (EM) distributary. Its opening and gradual enlargement since 1982 are evident from multiple lines of observation: Between 1984 and 2021 the discharge ratio between the EM and the Athabasca River more than doubled, increasing from 9% to 21%. The EM has widened by +53% since 1984, whereas the Athabasca River channel width has remained stable. The downstream Mamawi Creek delta is growing at a discharge-normalized rate roughly twice that of the Athabasca River delta in surface area. Longitudinal global navigation satellite systems field surveys of water surface elevation reveal the EM possesses a ∼2X slope advantage (8 × 10 −5 vs. 4 × 10 −5 ) over the Athabasca River, and unit stream power and bed shear stress suggest enhanced sediment transport and erosional capacity through the evolving flow path. Our findings: (a) indicate that a slow avulsion of the Athabasca River is underway with potentially long-term implications for inundation patterns, ecosystems, and human use of the PAD; and (b) demonstrate an observational approach for identifying other slow avulsions at river bifurcations globally.Plain Language Summary Avulsions shift river courses and move water and sediment to new channels, which affect infrastructure, floodplains, and ecosystems. Slow avulsions take decades to develop and are more difficult to identify. Using on-the-ground measurements and 37 years of Landsat satellite imagery, we analyze gradual channel changes in the Peace-Athabasca River Delta (PAD), Canada. The Athabasca River is changing course such that more of its water enters its westernmost outlet, the Embarras River-Mamawi Creek (EM) channel. Multiple lines of evidence demonstrate that the EM channel has been gradually opening since 1982. Between 1984 and 2021, the water entering the EM channel increased from 9% to 21% of the river's total flow. Since 1984, the EM channel has widened by 53%, while the Athabasca River channel has remained stable. The delta forming at the EM mouth (i.e., Mamawi Creek delta) has grown twice as fast as the Athabasca River delta. Field measurements of water surface elevation show the slope of the EM channel is twice as steep as the slope of the lower Athabasca River (8 × 10 −5 vs. 4 × 10 −5 ). Because water tends to flow down the steepest slope, we expect more water to flow down the EM channel in the future. Our findings indicate a slow capture of Athabasca River water into its EM channel, with potenti...

Effects of Climate Change on Navigability Indicators of the Lower Athabasca River, Canada

“…The latter result indicates that this period of interest was historically not always ideal for boating, which is further supported by the findings that the revised Aboriginal Extreme Flow (AXFR; 500 m 3 s −1 ) exceedances (POT500) after week 34 have been generally decreasing, which aligned with a general decline in the Fall Aboriginal Navigation Index In addition to climate impact on streamflow magnitude and timing, fluvial geomorphological processes that shape water movement within deltaic environments warrant monitoring the water depth at key sites (i.e., pinch points), which currently and may yet pose problems to navigability. Such an example is channel avulsions in the early 1980s that re-routed Athabasca River water and sediments towards the heart of the delta and led to navigability issues identified as part of community-based monitoring [42,71,72].…”

“…In addition to climate impact on streamflow magnitude and timing, fluvial geomorphological processes that shape water movement within deltaic environments warrant monitoring the water depth at key sites (i.e., pinch points), which currently and may yet pose problems to navigability. Such an example is channel avulsions in the early 1980s that re-routed Athabasca River water and sediments towards the heart of the delta and led to navigability issues identified as part of community-based monitoring [42,71,72].…”