3.4 Connectivity Regimes
Across the 2018 study period, sites identified as stable (Cdur = 0% or 100%; Outflow, Main-Mid, & Pond-Iso) had generally unimodal distributions of connectivity strength with modes at high or low values (Figure 6). In contrast, distributions of connectivity strength at the remaining seven sites with intermittent connectivity, had wide spread and a dominant mode at lower connectivity values and a secondary mode at high connectivity values (Figure 6). Within the intermittent target sites, some sites such as Side-03 and Pond-Con-02 exhibited rapid shifts between modes with few observed sample dates with intermediate connectivity strength while others including Pond-Con-01, Side-01, and Side-02 exhibited more gradual behavior with intermediate connectivity strength values for a larger proportion of the study period (Figures 3 & 6).
Aggregating site specific results to the river-floodplain system reveals transitions in system connectivity. At high flows, conditions are more homogenous and there is relatively high connectivity across the entire river-floodplain system (Figure 7a & b). Conversely, there was a bimodal distribution of river-floodplain connectivity at lower flows with some sites remaining connected and others becoming disconnected from Inflow. The mean value of σm across the river-floodplain system was positively related to Inflow stage (Figure 7c), whereas the variance in connectivity, as derived from the standard deviation of σm, was highest during intermediate flows (Figure 7d).
At the river-floodplain system scale, we also found that defining binary σm connectivity thresholds to describe the system wide behavior can be sensitive to the chosen σm threshold value (Figure 8). We varied the threshold between the 10th to 90th percentiles of σm and observed the effect on exceedance probabilities of how many sites are connected in the 2018 study period. Varying σm thresholds between 0.4 to 0.6 generated small shifts in the exceedance probabilities distributions. Outside that range, exceedance probability distributions exhibited larger changes in their shape (Figure 8).