Geomorphic study
In order to obtain a large set of data points, active channel width was
measured using current orthophotos with GIS software (ArcMap 10.5,
2017). Active channel width was measured between the channel banks,
perpendicular to the downstream direction, every 50 m. Several other
geomorphic factors were also recorded, including the process domain as
identified from the orthophoto, the surficial geology, and proximity to
glacial features (e.g., eskers, moraines). Surficial geological deposits
were recorded in four different categories (bedrock, peat, subglacial
and deltaic fine sediment (including postglacial clay, silt and sand and
subglacial sands), coarse till). Using a 2-m digital elevation model, we
determined the channel slope and the drainage area at each measured
transect, the latter of which was used as a proxy for bankfull
discharge. We then plotted the power relationships between drainage area
and channel width for all transects and each process domain separately
to determine whether the stream networks conform to expected downstream
hydraulic geometry relationships.
To predict channel width we used multiple regression models, based on
drainage area distance downstream from lake, channel slope, proximity to
glacial feature, and type of surficial geology deposits (categorical).
Selection was based on lowest AIC with backward-step selection. The
relationship between channel width and drainage area were analysed using
power regressions. Multiple linear regressions were used to determine
logged values of power regression. All statistical analyses were
performed in R studio version 3.6.0 (R Core Team, 2021).