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.
<< INSERT FIGURE 5>>
Figure 5: Potential overland flow convergence pathways, major
trackways and summary first order observed rill density in
cultivated plots.