Due to the interpolation the land surface is very smooth and does not show any geomorphic details such as the dam, its breach or the gully cut through the sediments. DTM A still allows to recognize main geomorphic features, such as the slope and riverbed, but it is unsuitable for our badland volume analysis. Due to internal algorithms the resolution of the generated DTM generalized to a cell size of at least five times the GSD (in our case: 5 × 3.12 cm per pixel). This is two and a half times the resolution of the DTM B (derived from the UAV imagery): 0.1562 × 0.1562 m per pixel. DTM A (derived from the contour lines) has a resolution of 0.383 × 0.383 m per pixel. As presumed, they differ in their resolution and level of detail.
Two DTMs were created, one based on the 20 m contour lines from NGO Service of South Africa (DTM A) and a second one based on the UAV imagery directly produced by the Pix4Dmapper Pro software (DTM B, Fig.
