Monitoring geomorphic and hydrologic change at mine sites using satellite imagery: The Geita Gold Mine in Tanzania

• We assess geomorphic and hydrological change using multi-date DEM data.
• DEM change mapping reveals accurate depictions of gold mining activities in Tanzania.
• Substantial hydrologic change to streams is predicted.

Large surface mining operations typically involve not only multiple pits but also the creation of new “mountains” of tailings. These operations dramatically change the local watershed topography and expose downslope agricultural fields and forest to tailings runoff. Given that most mine tailings expose large quantities of surface area to oxidation and transport by water, any heavy metals associated with the deposit are mobilized to move along with the runoff. In Tanzania, the Geita Gold Mine (GGM) area is such a site and the Government of Tanzania has yet to develop a water monitoring network to protect villages adjacent to the mines. As a result, mining company data are the only data available to monitor water supply and quality. Typically in mining and oil sand extraction, geospatial data are used to report and monitor land reclamation at the mining site, and while these efforts are useful, they do not consider hydrologic changes and risks. In this paper we evaluate the use of Digital Elevation Model (DEM) data from the Space shuttle Radar Topography Mission (SRTM) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) in an effort to identify the changes in local topography and surface hydrology around the GGM and assess the implications these changes have for the potential increased mobility of tailings and their effects upon farmers, village water supplies, and community forests using a hydrologic flow model. Results reveal that over 13 million m3 of material has been removed from the main mining pits at GGM while over 81 million m3 of material has been deposited elsewhere in tailings piles and waste dumps. These topographical changes have had a profound influence on the local surface hydrology, with some stream channels shifting up to 3 km from their original paths. Overall, approximately 37 km2 of cultivated land is within the watersheds associated with potentially polluted streams and that future mining operations could impact up to 63 km2 of cultivated land.