3.2 Structural connectivity framework and observed erosion
Comparison of potential flow pathways (grey convergence lines, Figure 5) and observed density of rills (white-grey-black shaded plots in Figure 5) reveal a disconnect in potential and actual development of rill erosion in some plots. Plots coloured white have a low (<0.0005 m2 m-2) density of rill features observed in the drone survey and there are several notable examples where the topography-driven model predicts flow convergence but no rill erosion features were observed (e.g. northeastern sector, labelled A, Figure 5). Equally, however, there are plots where topography predicts flow convergence which correlated with observations of high-density rill erosion (> 0.007 m2 m-2) (e.g. south eastern sector, area B, Figure 5). Herein there is a notable strip plot showing no erosion features that had apparently been cultivated shortly before the drone survey (see Figure 2a) highlighting potential limitation in the approach with respect to cultivation duration and timing prior to survey. Area C is notable again for lack of erosion features given potential convergence line density wherein these fields also have limited potential for overland flow run-on given track along upper slope. These areas can be compared to area E in the open pastoral land where severe erosion was observed, linked to overspill from the track (Figure 4). In comparison to area B, cultivated area D is notable for lack of erosion features given potential for higher order flow convergence routing wherein observational evidence of crop growth indicates potential rill features have not been cultivated out in this instance. It is also noteworthy that the area upslope of these plots remain under semi-natural vegetation cover compared to area B and that there is no major difference between area D and B in terms of slope angles (Figure 3b). In the more recently converted plots of area B, ca 90% of the area with potential for flow convergence showed moderate or high density of rill erosion features. In area D, the established agricultural plots, ca 40% of the area with potential for flow convergence showed moderate rill erosion density.
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Figure 5: Potential overland flow convergence pathways, major trackways and summary first order observed rill density in cultivated plots.