Identifying Ice-Jam Flooding Events through the Application of
Dendrogeomorphological Methods
Abstract
In this research, we explore whether a dendrogeomorphological assessment
of tree scarring can accurately summarize past ice-jam flooding events
occurring at a given reach of a river. A sample site was chosen with a
history of ice-jam flooding located in close proximity to a river gauge
station. Samples were collected along a 200-metre stretch of riverbank
to capture the variation in elevations and possible different ice-jam
flooding events. Disk samples were collected from trees with visual
scarring evidence that indicated they had endured a past ice-jam event.
Tree cores from an adjacent stand were collected to create a master
chronology for each of the sampled species. Tree disks and cores were
analyzed under a microscope using a Velmex stage system, then visually
and statistically crossdated using the program COFECHA. Based on the
last year of tree growth, years of individual injury events were
established. The years of injury event dates were compared against the
years of highest instantaneous maximum water elevations from gauged
river data. The two data sets correlated, as years with highest recorded
injury event dates were also the years of highest instantaneous water
level elevations. The most common years of injury event dates were
directly reflected in the top five years of highest river instantaneous
water level elevations. In addition, the year of 2020 had the highest
water elevations in the past 27 years, which was again reflected in the
dendrogeomorphological data as the injury event year of 2020 was
recorded on over 90% of the sampled tree disks. The correlation found
between the gauged river data and the dendrogeomorphological data
strongly suggests that past ice-jam flooding event dates can accurately
be determined through the analysis of trees in riverbank stretches that
have been impacted by ice-jams. The relationship of the gauged river
data to the dendrogeomorphological data will therefore allow researchers
to determine ice-jam site histories in remote areas where no gauged data
exists. The site histories can provide information such as the years or
heights that past ice-jam flooding occurred, which could then be used in
ice-jam flooding hazard assessments.