Particular areas such as streams, rivers, and deep gullies, where the
vertex or elevation values appeared to be erroneous,were also corrected
manually using 3D break-lines. Finally, the DTM was hydrologically
corrected using SAGA to allow extraction of
derivatives such as slope, flow direction, specific catchment area (SCA)
and sub-watersheds. These derivatives, along with the DTM, were used
as input layers for OOA.