Application of laser scanning and photogrammetry in the evolution process of slope erosion

Soil erosion on a slope is one of the most serious soil degradation that caused by the complex dynamic process of water draining down the slope. Quantitative monitoring of the slope erosion process is of great practical significance to clarify the erosion mechanism for the better models in the recent years. A non-contact measurement has been widely used, such as the laser scanning or photogrammetry, due to the high efficiency and accuracy. However, it is still lacking on the accuracy and applicability evaluation in the process of slope erosion, especially for the rill morphology characteristics. In this study, the laser scanning and photogrammetry were selected to monitor the evolution of soil slope erosion under the indoor artificial rainfall, in order to quantitatively explore their accuracy and applicability. The red soil was collected with the granite parent material from the Changting County, Hubei Province, China. The test material was then selected as the leaching, sedimentary, and parent material layer from the bottom to the top at the sampling point. The soil trough was used with the size of 4.0 m (length) × 2.0 m (width) × 0.60 m (height), particularly with the depth of soil filling of 0.50 m. The soil was then filled with the 0.15 m thick parent material layer, 0.20 m sedimentary layer, and 0.15 cm leaching layer before the test. The soil tank was subjected to the multiple cycles of drying and wetting. The static settlement was set at least two months, in order to make the soil layers and particles as close as possible to natural conditions. The whole duration was 1 h for the single-field simulated rainfall or runoff test after the runoff on the slope surface. The total rainfall was 100 h, where the interval was 24 h between each two intermittent rainfall. The rain intensity was also set to (90±5) mm/ h. The sediment ocean was then collected during the rainfall. After that, the 3D laser scanning and close-range photogrammetry were employed to record the micro-topographic and surface morphology of the slope at each rainfall interval. As such, the digital point cloud was obtained on the slope surface after the rainfall. At the same time, the length, width and depth of each rill on the slope were measured at the intervals of 10 cm, in order to determine the evolution of the morphological characteristics of the slope rill. The characteristic parameters of rill morphology were calculated to collect the runoff sediment and measurement. A comparison was also made on the laser scanning and photogrammetry technology in the erosion monitoring test. The results show that: 1) The slope erosion process was divided into the sheet erosion, rill development and maturity stage, according to the different dominant erosion. 2) Both non-contact measurement methods performed better to accurately measure the slope erosion. Specifically, the maximum relative error was -16.82% for the process of sediment production. The better applicability was also achieved in the measurement of slope erosion quality. 3) The close-range photogrammetry technology was superior to the 3D laser scanning in the monitoring slope erosion and sediment production, rill depth measurement, and slope micro-topography simulation. Therefore, the digital expression was realized for the evolution process of slope erosion, in order to promote the high efficiency and high precision of slope erosion monitoring. The finding can also provide the strong reference in the technology selection for the soil slope erosion.