4.1 Translating people-land-water connectivity evidence into
targeted mitigation actions
The modelled flow lines between different catchment areas map indicate
direct hydrological connection between severely eroded pastoral land in
the mid and lower slope regions of the catchment (Figure 6e) with
upslope runoff generation on cultivated plots. Connectivity is enhanced
through interconnection of major tracks with natural flow convergence
lines, where downslope gully onset was often initiated directly below
road channels entering the rangelands (exemplified again in Figure 6e).
The whole catchment view of this study is critical in underpinning
community-led action. These observations also have important
implications for track management and planning of runoff drains that can
release water and eroded sediment and nutrients back into the fields.
Within plot improvements in soil infiltration capacity to reduce
overland flow generation (Kuyah et al., 2019; Nishigaki et al., 2017) is
key as is improvement of and aggregate stability, e.g. with amendment by
organic matter, to reduce risk of soil capping/crusting (Laker and
Nortjé, 2019; Smith et al., 2019) and improve overall soil health
(Belayneh et al., 2019; Mesfin et al., 2018). While such within-plot
actions can be locally beneficial, analysis in this study has shown that
different agricultural plot terraces on the same slope are chained to
each other. At the edge of plots, implementation or augmentation of
features that can attenuate or slow overland flow to retain soil within
the plots are important but poor practice upslope, however, can generate
significant overland flow that overwhelms the integrity of downslope
plot terraces, even if the latter uses conservation agriculture
practices that promote infiltration and good soil health. Herein slope
length is a key factor (Gourfi et al., 2018). This is exemplified in
zone B1 and B2 where slope length was high (< 800 m) and the
relatively recent conversion of the land with under-developed boundaries
meant that attenuation features could not cope with the amounts of
overland flow generated. This allowed an extensive and well-connected
rill network to develop and link all plots to each other and the main
track (Figure 6b). This was augmented by a large proportion of plots
cultivating crop rows in the direction of slope even though the plots
themselves, and their boundaries, were aligned across the slope.
Off-contour cropping is widely known to enhance rill development (Ayele
et al., 2018). In contrast, visual evidence of rilling was markedly
lower in the longer established plots (e.g. zone D) where farmers have
used contour ploughing and the plot boundaries themselves are more
closely aligned with contours. While the upper slope angle is still
high, the hilltop steep land has been left in natural vegetation both
reducing run-on from the upslope contributing area and effectively
reducing the overall length of the slope segment. With the longer-term
establishment of plot boundaries there is further resilience to
development on connected rill networks due to edge-of-plot barriers that
are not overwhelmed by any overland flow that does occur under extreme
rainfall conditions. The strong influence of the direction of crop lines
is further exemplified by comparison of the two valley sides of Zone A
(Figure 6a).
Comparison of the longer-established cultivated plots and recently
converted land in this study highlights a problem in the initial phase
of slow-forming terraces, as not enough time has passed for the buffers
to become effective in stopping flow and the slope gradients to
decrease, giving almost free reign to erosive processes. The community
picked up the key issue of plot boundary integrity and flow retardation
by natural vegetation, wherein suggestions of planting trees and
permanent grasses were made. The integration of people, land and water
into one connectivity framework exposed a direct chain of cause and
effect that can promote cooperative community-led mitigation to stop the
downstream propagation of runoff. This is potentially facilitated by the
agro-pastoral structure of the community, wherein farmers are both
dependent on cropland and on the rangelands for livestock grazing,
presenting an opportunity for integrated catchment management.