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Mapping Temporal Changes of Erosion and Potentially Acid Generating Material on Abandoned Mine Lands using Remotely Piloted Aerial Systems
AuthorCramer, Alison Susan
AdvisorMcCoy, Scott W
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Erosion, transport, and weathering of potentially acid generating material (PAGM) on abandoned mine lands (AMLs) can degrade downstream environments and contaminate surface and groundwater resources through exposure to acid mine drainage (AMD) and secondary sulfate minerals. Current AML monitoring techniques rely on field measurements, which can make monitoring the thousands of AMLs for exposed PAGM and erosion of cover material on mine waste rock piles time intensive. Remotely Piloted Aerial Systems (RPASs) provide a platform that can be combined with remote sensing and structure from motion photogrammetry techniques to quantify erosion from mine waste covers, and to map the temporal dispersion of PAGM. Here, we explore the use of RPASs as a complementary remote sensing platform to quantify erosion and map the spatial and temporal changes of PAGM on a mine waste rock pile remediated with a soil cover at the Perry Canyon, NV, USA AML. We carried out eleven flights over 29 months. We built five different mm resolution 3D point clouds using a RPAS equipped with a standard camera. We focused on quantifying erosion of the soil cover and erosion and deposition occurring in the creek adjacent to the mine waste rock pile. From these data, cm-scale surface changes on waste rock piles, soil covers, and subsequent erosion and deposition in the adjacent stream were mapped. Quantitative differencing of point clouds showed that 10.2 m3 of soil cover and waste rock were eroded over a 29-month time period. Additionally, we measured continued incision of the distinct rill network incised into the mine waste rock pile, indicating active and focused removal of cover material. Using a RPAS equipped with a 5-band multispectral sensor measuring in the visible to near infrared (400-1000 nm), we created six different 3 cm resolution orthorectified reflectance maps. We focused on testing the ability of established supervised and unsupervised classification algorithms to map PAGM on imagery with very high spatial resolution, but low spectral sampling. The unsupervised method produced similar maps of PAGM, as compared to supervised schemes, but with little user input. Our classified multi-temporal maps, validated with multiple field and lab-based methods, revealed persistent and slowly growing 'hotspots' of jarosite, a secondary sulfate mineral, on the mine waste rock pile. The mapping methods we detail for RPASs carrying a broadband multispectral sensor can be applied extensively to AMLs. RPASs with standard cameras can provide high resolution data sets to calibrate and test erosion and transport models for more accurate predictions of cover maintenance and design. Our methods show promise to increase the spatial and temporal coverage of accurate maps critical for environmental monitoring and reclamation efforts over AMLs.