3.2 Process connectivity framework and observed erosion
In terms of process connectivity overland flow enhancement factors,
on-the-ground measures of soil infiltration capacity and soil
erodibility (aggregate stability) across the different agricultural
plots was beyond the scope of this drone survey-based study. We
hypothesised, however, that at a higher level, correlation of plot
cultivation direction with high density of rill erosion could be
illustrative of cultivation controls on potential overland flow
generation in the context of process connectivity concepts that
encompass impacts on overland flow generation and slope length.
<<< Insert Figure 6
>>>
Figure 6: Aerial photographs of key illustrative zones showing field
boundaries, cropping practice and incidence of rill erosion.
Zones of different time since plot establishment, configuration and
within plot practice showed different degrees of rill density and
network development (Figure 6). In zone B, where the greatest density of
rill erosion was observed, there were two main rill networks (labelled
B1, B2, Figure 7) connecting upper slope to lower and discharging onto
the main track running E-WSW which ultimately spills across the pastoral
land at E. The agricultural plots in B1 are oriented across slope so
boundaries traverse any potential flow lines in accord with local ‘good
practice’ but cultivation lines within the plots are largely in the
direction of slope (indicated by amber and red arrows, Figure 7), with
the exception of the lowermost plots. On top of that, the higher plots
are also developed on very steep slopes (>12°). In zone B2,
again the plots themselves are largely and appropriately orientated
across the slope but within plots, there is a mosaic of cultivation
directions. The rill network on this slope is well developed and crosses
all cultivated plots connecting them to the main track way. It is also
important to note that the slope length on these plots is also longer.
<< INSERT FIGURE 7 >>
Figure 7: Comparison of first order rill density data and orientation of
cultivation with respect to slope
Zones A and D contrast with the situation of zone B. Both zones A and D
show more moderate observation of rill density (Figure 6). In zone A,
the plots are contoured around a valley head. Plots to the northern side
have crop lines contoured with plot boundaries (green arrows, Figure 7)
and little evidence of rill erosion. To the southern side, crop lines
show some alignment to slope (amber arrows, Figure 7) and there is
moderate rill erosion in the lower plots (Figure 6). In Zone D, plot
boundaries are more exactly contoured to topography than zone B (Figure
6) and there is only one incidence of cultivation lines being with the
slope, the remainder being intermediate or contoured. Rills in this area
do not display the same level of development and connectivity as zone B.
Zone C offers a different scenario where while cropping lines are
contoured, moderate rill erosion was determined (Figure 7) and
apparently concentrated along plot boundaries before overtopping
edge-of-field bunds (Figure 6). The extensive erosion of gentle to
moderately sloped pastoral land, zone E (Figure 6), occurred at the
outlet of the track fed by extensive rill erosion in zone B with some
contribution from zone C.