3.1 Topography and land cover
Derived land cover classes (Figure 3a) were broadly spread across cultivated plots (26%), open pastoral land (30%) including homestead farm areas with sporadic tree and shrub cover and exposed soil surfaces in and around village buildings. Areas with patchy grass and rough shrub cover, often with intermittent soil loss and vegetation disturbance due to erosion, were classed as scrub (10%). Areas of notable bare ground were observed in the severely eroded mid to lower slope region (Figure 4) that receives much of the concentrated overland flow from the hillslopes above.
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Figure 3: (a) land cover classification and (b) derived mean slope for cultivated plots
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Figure 4: Severely degraded pastoral land in the mid to lower region of the catchment (photos Carey Marks/University of Plymouth, taken March 2017)
The cultivated plots occupied the east and southeastern side of the catchment upland zone and hence represent potential overland flow contribution areas to the mid and lower slope gullied zones. The group of cultivated plots to the east of the system are the most recently converted (from open grazing to cultivation) land (ca 1-3 years prior to survey) with boundaries set to shallow ditches and bunds akin to ‘slow-forming’ terrace approaches (Chapagain and Raizada, 2017; Dercon et al., 2003). Vegetation along these boundaries was largely immature grasses. The cultivated plots to the south were more established (over 7 years) with notable establishment of edge-of-plot bunds and mature vegetation along boundaries. In both areas of cultivation, uppermost plots showed steeper slopes (Figure 3b) graduating to more gentle slopes toward and on the open pastoral land.
The cultivated land plots are interconnected with unmetalled trackways commonly used to drive livestock and for pedestrian and motorbike access. All tracks are incised to varying degrees with notable incision on downslope reaches of tracks from upper cultivated plots. Severe erosion of pastoral land originates from apparent overland flow spill over and concentration from track in centre west of the study area (Figure 3b). Severe gully erosion has resulted in upslope relocation of the track on more than one occasion.