Abstract
Unmanned Aerial Systems, or drones, are very helpful tools for managing open-pit mining operations and developing ecological restoration activities. This article presents a method for identifying water erosion processes in active quarries by means of drone imagery remote sensing, in the absence of pre-existing imagery or mapping for comparison. A Digital Elevation Model (DEM) with a spatial resolution (SR) >10 cm and an orthophoto with an SR >2.5 cm were generated from images captured with a drone and their subsequent photogrammetric processing. By using Geographical Information Systems tools to process the DEM, a detailed drainage network was obtained, the areas of detected water erosion were separated, and the watersheds in the gullies identified. Subsequently, an estimated DEM before the erosive processes was reconstructed by interpolating the gully ridges; this DEM serves as a reference for the relief before the erosion. To calculate the volume of eroded material, the DEM of Differences was calculated, which estimates the volume difference between the previously estimated DEM and the current DEM. Additionally, we calculated the material necessary for the geomorphological adaptation of the quarry and the slope map, which are two valuable factors closely related to the monitoring of erosive processes. The results obtained allowed us to identify the erosion factors quickly and accurately in this type of mining. In the case of water-filled quarries, it would be important to characterize the subsurface relief. Essentially, the presented method can be applied with affordable and non-invasive materials to create digital grid maps at 10 cm resolution, obtaining data ready for 3D metrics, being a very practical landscape modelling tool for characterizing the restoration evolution of open-pit mining spaces.
Highlights
The methodology used for estimating the pixels corresponding to channels and watersheds, according to a method previously tested and implemented in morphometric [43] and hydrologic [44] analysis, was applied in this research with success in drone imagery, and enabled us to construct an estimated Digital Elevation Model (DEM) (DEMT0 ) using the points of the dense point cloud located over the watersheds of DEMT1
As demonstrated in this study as well as previous literature, remote sensing using drone-acquired imagery is a very useful tool for the morphometric characterization of terrains in open-pit mining activities, especially for erosion processes related to restored areas
We described a new strategy for estimating the DEM before the erosion process by using well-known GIS techniques based on hydrologic analysis
Summary
Extracting raw materials such as sand, gravel, crushed stone, brick clays, gypsum, and ornamental stones requires intensive and extensive efforts as all of these products are obtained from open-pit mining operations [1]. Public awareness of sustainable land management has been growing, and since the 1990s, environmental policies and restoration actions have been increasingly focused on addressing environmental impacts [3]. In this type of mining, exploitation occurs in phases where the extraction of materials is linked with the ecological restoration of previously exploited areas, which generally includes geomorphological adaptation [4]. Open-pit mining can trigger erosive processes and landslides depending mainly on four principal factors (soil or substrate characteristics, vegetative cover, topography, and climate) [5]
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