2.6 Multiple Year Comparison
To compare connectivity dynamics across multiple years, we made use of
five years of seasonally monitored water levels (May through September)
at Inflow, starting in 2016 through 2020. These stage records were
collected with TruTrack Capacitance Rods and were summarized to mean
daily stage. As several data gaps in the record exist, we imputed gaps
using spline regressions with daily streamflow records from a nearby
USGS gage at the Big Thompson River below Moraine Park, Colorado (USGS
#402114105350101) (Figure S5). As seasonal hysteresis was observed in
the relationship between the North St. Vrain and Big Thompson rivers,
spline regression equations were fit separately for the rising limb and
falling limb, which were respectively defined as prior and post peak
seasonal flow at the North St Vrain.
From this five year record of Inflow stage, we used the connectivity
strength models developed for each target site within the 2018 study
period (described above) to predict daily connectivity strength values
at each target site across all five years from 2016 to 2020 between May
01 and September 30th. To examine how much inter-annual variability was
observed at target sites within the river-floodplain system, we
calculated the duration of high connectivity (σm ≥ 0.6),
intermediate connectivity (0.4 < σm< 0.6), and low connectivity (σm ≤ 0.4) at
each target site for each year. Intermediate connectivity was chosen as
between 0.4 < σm < 0.6 because
analysis of the connectivity strength functions suggest that at low
connectivity σm stabilized between 0.2 to 0.4, and at
high connectivity between 0.6 and 0.8. To examine the effects of
inter-annual streamflow variability across the river-floodplain system,
we calculated the daily fraction of target sites with high, intermediate
and low connectivity. Only the seven target sites with observed
intermittent connectivity in 2018 were included in this portion of our
analysis.
All analyses and related figures were generated in R version 3.6.1 (R
Core Team, 2016).