Mine site reclamation and closure involve reforming and/or covering waste material to minimize erosion by rain and wind storms. When exposure and transport of the waste material regularly occurs, mining companies can face significant perpetual costs associated with restoring the cover material.
UArizona has partnered with a mine in Arizona to understand where closure designs are succeeding and where persistent erosion has become a costly problem at closed mine sites throughout Arizona. UArizona seeks to expand this collaboration to other companies seeking cost-effective closure designs. The specific objective of this research initiative is to improve two-dimensional numerical erosion prediction models for application to erosion prone tailings embankments to improve erosion resilience following mine closure.
We welcome new industry partners to join this research cooperative. Please contact us for additional information. The contract Scope of Work (SOW) can be found below.
Image caption: Numerical model created by Dr. Pelletier helps designers and engineers understand how water is eroding slopes by identifying where waterways run through the structure.
Mine site reclamation/closure involves reforming and/or covering waste material to minimize erosion by rain and wind storms. When exposure and transport of the waste material regularly occurs, mining companies can face significant perpetual costs associated with restoring the cover material. At San Manuel, Arizona, some areas of the tailings embankment that were closed in 2007 are eroding nearly every year. UA has partnered with BHP to understand where covers are succeeding and where persistent erosion has become a costly problem. UA seeks to expand this collaboration to other companies seeking cost-effective closure designs. The specific objective of this research initiative is to improve two-dimensional numerical erosion prediction models for application to erosion prone tailings embankments to improve erosion resilience following mine closure.
At the San Manuel tailings embankments, deep gullies existed in some portions of the tailings embankment prior to closure. The closure process did not completely fill in these gullies and other features of the pre-closure topography, leaving subtle depressions that now focus runoff during rainstorms. Even the largest pieces of rock cover are eroded nearly every year in these depressions. If the closure design had filled in these gullies just a few more feet, the depressions and the persistent erosion associated with them would likely have been avoided.
The experience at San Manuel points to the need for closure designs to be evaluated before they are constructed using two-dimensional numerical models that predict erosion using input data for topography, rainfall, and cover-material characteristics. Nearly all of the widely used computer models for predicting erosion on reclaimed mine sites are one-dimensional, however – they model water and sediment flow down the slope but do not capture the focusing of flow into small depressions.
In response to this need, UArionza has developed a computer model, ROCKSTAB2D, that predicts the erosional stability of existing and/or alternative future cover designs, including the two-dimensional focusing of flow into small depressions that is driving erosion at the San Manuel tailings embankment. ROCKSTAB2D is paired with novel remote sensing data analysis techniques developed by UA, including the ability to map spatial variations in the threshold water flow required to trigger erosion related to variations in rock cover particle diameter and vegetation. The result is a workflow that allows high-resolution spatially distributed data for topography, rainfall, vegetation, and cover material characteristics to be integrated into an assessment of the likely cover performance under current and future climate scenarios. This workflow allows mining companies to see how changes to proposed cover designs may or may not lead to cost-effective improvements in long-term cover-design performance. In addition, current operations may benefit from making small changes to minimize the reforming of waste materials that might otherwise be needed to achieve a stable closure design.
Deliverables for participating companies:
- Initial planning meeting: A site visit will be conducted to identify the study area of most interest to each company, the questions to be addressed at this study site, all available remote sensing or geospatial data that can inform the questions to be addressed, and the data analyses and numerical modeling to be conducted.
- Remote sensing analysis: All available geospatial data layers will be compiled and statistical analyses will be performed to identify the dominant controls on erosion (for study areas that have experienced erosion).
- Numerical modeling: ROCKSTAB2D will be applied to each study site to evaluate the dominant controls on erosion by flowing water. For completeness, these results will be compared to more widely used models (e.g., The Revised Universal Soil Loss Equation (RUSLE), and the Water Erosion Prediction Project model (WEPP)) that are limited to one dimension.
- Annual report: Results for all of the participating companies will be summarized in an annual report available to all participants.
- Wind erosion: If requested, UA can apply data analysis and numerical models (i.e., Wind Erosion Prediction System or WEPS) designed to predict wind erosion to the study sites.