Effects of slope shape on soil erosion and deposition patterns based on SfM-UAV photogrammetry

• Runoff volumes and sediment yields from runoff plots changed with slope shape. • Less runoff and sediment occurred on the slope with a lower concave part and its combination slope. • Soil erosion–deposition patterns on different shaped slopes were variable. • Unmanned aerial vehicles can be used to monitor slope microgeomorphic changes. Slope shape as a consequence of erosional landform development plays a prominent role in soil erosion. Clarifying the distribution of soil erosion and deposition patterns on different shaped slopes is crucial for soil erosion control. The aim of this study was to decipher the effects of slope shape on soil erosion and deposition patterns under natural rainfall conditions based on high-resolution unmanned aerial vehicle (UAV) data and geographic information system technology. Structure from motion (SfM)-UAV photogrammetry was carried out in four runoff plots with various slope shapes during the rainy season in 2021. Digital elevation models (DEMs) were developed for each slope shape before and after the rainy season. In addition to collecting runoff and sediment, the DEMs of difference were analyzed to quantify soil erosion and deposition patterns on various slope shapes in the rainy season. Results showed that the runoff volumes and sediment yields induced by rainfall were markedly different among various slope shapes. The mean runoff volume and sediment yield from the concave-convex slope were 1.09 ∼ 2.69 and 1.33 ∼ 27.16 times those of the other three slopes, respectively, with less sediment loss from the convex-concave slope and its combination slope. Slope shape exhibited a notable effect on the type of slope erosion and deposition. All four slopes showed considerable changes in surface elevation after the rainy season. The increase and decrease in surface elevation were concentrated in the range of –0.02 to –0.007 m and 0.007 to 0.02 m, respectively, with a low proportion of changes less than –0.03 m and greater than 0.03 m. The effectiveness of SfM-UAV in monitoring the microgeomorphic changes of slopes was verified by the consistency of soil erosion amounts based on sediment collection and SfM-UAV measurements. Reference values were provided to solve the threshold problem of slope length cutoff in soil erosion prediction models based on runoff plot experiments. Findings of this study could be useful for decision-making in soil erosion control and slope reconstruction.