Floodplain stratigraphy of the ice jam dominated middle Yukon River: a new approach to long‐term flood frequency

Abstract

Abstract:Floodplain stratigraphy is used as a new method for reconstructing ice jam flood histories of northern rivers. The method, based on reconstruction of the sedimentary record of vertically-accreting floodplains, relies on stratigraphic logging and interpretation of floodplain sediments, which result from successive ice jam floods, and radiocarbon dating of inter-flood organic material for chronology. In a case study along a reach of the Yukon River that straddles the Yukon-Alaska border, the method is used to develop a record of ice jam flooding for the last 2000 years. Detailed chronostratigraphic logs from three sites along the Yukon River indicates that the long-term recurrence interval varies depending on location, but ranges from approximately once in 25 years to once in 38 years (or a probability of ca 3-4% in any given year). This is broadly similar to the 4Ð5% probability of recurrence calculated from archival and gauged data at Dawson City, Yukon Territory, for the period 1898-2006. Two of the three study locations, with sufficient chronology, suggest a decrease in flood frequency in the last several hundred years relative to the preceding period at each site, broadly corresponding to the Little Ice Age, suggesting climate exerts some control over long-term ice jam flood frequency. This study demonstrates that the floodplain sedimentary record offers the potential to extend records of ice jam flooding in remote, ungauged northern rivers and provides a broader temporal context for assessing the frequency and variability of ice jam flooding.

Application of Floodplain Stratigraphy to Determine the Recurrence of Ice-Jam Flooding Along the Lower Peace and Athabasca Rivers, Alberta

“…Floodplain sediments have been used extensively to reconstruct paleoflood frequency in a wide variety of physiographic and climatic settings (Brackenridge, 1981;1988;Kochel and Baker, 1982;1988;Baker et al, 1983;Ely and Baker, 1985), but only recently has the method been applied to ice-jam floods. Along the Yukon River Livingston et al (2009) showed that floodplain exposures containing repetitive overbank flood-deposited sediment layers separated by organic material can be used to reconstruct long-term ice-jam flood frequency. The sediment layers (flood beds) are slackwater deposits that accumulate on the floodplain surface during high magnitude ice-jam floods.…”

“…In a recent study Livingston et al (2009) used floodplain stratigraphy to reconstruct a 2000-year ice-jam flood history of a segment of the Yukon River straddling the Yukon-Alaska border. The method is based on the recognition of distinct, repetitive overbank flood-deposited sediment layers (beds) separated by organic material.…”

“…The method developed by Livingston et al (2009) was used to reconstruct the ice-jam flood history of the lower Peace and Athabasca Rivers and thereby extend the record of ice-jam flooding within the PAD beyond the current limit of 300 years. This investigation addresses a key research gap concerning the natural variation of icejam induced flood extent and frequency (Peterson, 1995, p. 86).…”

“…Here, the floodplain sedimentary archive is investigated as a stratigraphic proxy indicator of ice-jam flooding along the lower Peace and Athabasca Rivers, Alberta. This relatively new method involves stratigraphic logging and interpretation of floodplain sediments resulting from successive ice jam floods and radiocarbon dating of inter-flood organic material for chronology (Livingston et al, 2009). At six sites the method is used to extend the record of ice-jam flooding by up to 1500 years, providing the longest temporal framework for assessing the recurrence of ice-jam flooding in the Peace-Athabasca Delta (PAD) to date.…”

“…Ici, les archives sédimentaires de la plaine inondable sont étudiées en tant qu'indicateur de substitution stratigraphique des inondations causées par les embâcles le long du cours inférieur des rivières de la Paix et Athabasca, en Alberta. Cette méthode relativement nouvelle fait appel à la diagraphie stratigraphique et à l'interprétation des sédiments de la plaine inondable qui résultent des inondations successives causées par les embâcles ainsi qu'à la datation au carbone 14 de la matière organique entre les inondations à des fins de chronologie (Livingston et al, 2009). À six sites, la méthode est employée afin de faire remonter jusqu'à 1500 ans l'enregistrement des données sur les inondations causées par les embâcles, ce qui constitue le cadre temporel le plus long pour l'évaluation de la récurrence des inondations causées par les embâcles dans le delta des rivières de la Paix et Athabasca à ce jour.…”