New insights into the spring flood history of the lower Peace and Athabasca Rivers, Northern Canada

Abstract

Terrace floodbed sediments provide a key to understanding riverine flood history but to date floodbed chronologies have been limited in their temporal resolution. This study reconstructs the spring flood frequency, magnitude, and sediment delivery of the Peace and Athabasca Rivers at the Peace-Athabasca Delta (PAD), northern Canada, for the past four centuries through an algorithm that relates time to total organic matter accumulation in terrace floodbeds. The floodbed chronology is then compared to the historic flood record. Flood frequency, floodbed thickness (flood magnitude), and sediment accumulation histories were site-specific and therefore required integration across sites to produce cogent histories. Floodbeds record a lower flood frequency than the historic record because they tend not to register small or moderate floods that may not overflow the high terraces. Over the past 400 years, the Athabasca River experienced secular trends of increasing flood frequency and sediment delivery and a multicentury fall then rise in flood magnitude. Peace River flood frequency and sediment delivery peaked sometime early in the 20th century while flood magnitude peaked in the late 1800s. The temporal pattern for flood magnitude of the Peace and Athabasca Rivers was negatively correlated. Athabasca River decadal flood frequency and magnitude were positively correlated. Trends of declining Peace River flood frequency, magnitude, and sediment delivery expressed over much of the 20th century may have reversed in the past 20 years. Since year 2000, flood frequencies of the Peace and Athabasca Rivers have exceeded their 20th century averages. Predictions of ecological changes and the fate of the Peace-Athabasca Delta need to be grounded in data. Hopefully these findings will help to dispel misconceptions about the PAD's history and serve to tether predictions about its future to reality.