Change Detection on Abandoned Mine Lands Using Unmanned Aerial Systems

Abstract:

Erosion, transport, and weathering of waste rock in abandoned mine lands (AML) can degrade downstream environments and contaminate surface and groundwater resources through exposure to heavy metals and acid mine drainage (AMD). Current AML monitoring techniques rely on time intensive field measurements, which make it difficult to quantify erosion and map downstream deposition of potentially contaminated sediments. We present a case study of the Perry Canyon, NV AML to explore the use of Unmanned Aerial Systems (UAS) as an easy-to-deploy platform utilizing structure from motion photogrammetry techniques to quantify geomorphic change. We created a 29-month time series composed of six seasonal UAS flights and differenced consecutive mm-scale three-dimensional point clouds. We quantified cm scale geomorphic surface changes on a waste rock pile and the adjacent creek and mapped downstream deposition of waste rock. We found that the majority of change occurred during the particularly wet winter and spring of 2018/2019, primarily through undercutting of the waste rock pile by Perry Creek and subsequent slumping of the waste rock cut slope. During this period of high runoff ~33 m³ of cover and waste rock were eroded, which was the majority of the cumulative sum, 47 m³, of cover material removed over the total 29-month study. We also measured continued incision of the distinct rill network in the waste rock cover incising at rates of at least 3.8 cm/yr. This highlights that erosion concentrated in the rill network with current depths on the order of decimeters are actively removing cover material. In total, these results show that the use of UAS in environmental research can increase the spatial and temporal coverage and the accuracy of monitoring efforts in AML, as well as provide high resolution data sets to calibrate and test erosion and transport models for more accurate predictions of cover maintenance and design.