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Geomorphic landform design and long-term assessment of tailings storage facilities in the Athabasca oil sands
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- Author / Creator
- Slingerland, Neeltje
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In stark contrast to historic mine abandonment, current international best practices in mine reclamation call for geomorphic designs and stability (physical and chemical) for a minimum of 1000 years. Current regulations in Alberta state that post-mining landforms shall be maintenance-free with equivalent land capability to pre-mining conditions, in line with accepted sustainability principles. However, external tailings storage facility (TSF) design in Alberta presently does not assess geomorphic changes due to erosion, nor has this potential risk been evaluated for the design life required. As the first of the oil sands TSFs prepare for closure, a quantitative estimate of erosion risk, and geomorphic assessment of present TSF closure design is necessary to evaluate long-term stability. Using a TSF in the Athabasca oil sands (AOS) within Alberta, Canada, as a study site, this research included five core components: 1) Geomorphic design for closure of the TSF using current best practices in the region, 2) identification, classification, and quantification of erosion on the active TSF using remote monitoring methods and subsequent evaluation of methods for potential use in closure monitoring, 3) proposed integration of geomorphic stability assessment in the tailings dams design process, 4) parameterization and application of the CAESAR-Lisflood LEM to the study site and a section of the dam slope to assess long-term geomorphology with three future climate change scenarios, and 5) assessment of five erosion mitigation design options for tailings dam slopes through stress-testing using CAESAR-Lisflood.
Both wind and water erosion were identified on the TSF dam slopes in the form of deflation, rills, and gullies. Using LiDAR and ‘Purview’ software with digital stereo aerial photography, the estimated annual soil loss from dams is 48.5 Mg/ha which falls into a ‘very high’ soil erosion hazard class. Neither of these remote methods provided all necessary information for post-closure erosion monitoring; however, in conjunction the methods were effective in identifying areas at risk, cause, and extent of erosion. Present design strategies for closure of TSFs in the AOS retain active dam slopes unaltered, which were found to be actively eroding at a high rate. Using CAESAR-Lisflood to simulate landform evolution, recent historic climate and a future climate scenario as represented through climate only and through cumulative effects (climate and vegetation change) generated large gullies that could pose a threat to dam stability. The cumulative climate change simulation resulted in greater soil loss over an extended time frame and erosion rates failed to stabilize over 100 years, while historic climate inputs lead to erosion rates reaching an equilibrium within about 20 years on the dam section modelled. When the entire TSF is simulated equilibrium erosion rates are attained within about 50 years. These results suggest that the current estimates for active dam maintenance and monitoring post-closure of less than 20 years are under-estimated. The majority of predicted erosion occurred on dams, with minimal impact to the geomorphically designed central plateau of the TSF. Integration of geomorphic design into the tailings dam downstream slope, followed by stress-testing, resulted in substantially less erosion than in other mitigation options simulated, including the geomorphic design with channel armouring. This indorses the concept that long-term stability of these landforms is best achieved by designing with nature rather than against it. -
- Graduation date
- Fall 2019
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- Type of Item
- Thesis
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- Degree
- Doctor of Philosophy
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- License
- Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.