Mine closure plans in Alberta’s oilsands are being made with a new advisor in mind: Mother Nature.
In the drive to build post-closure environments that are sustainable and reduce burdens for ongoing maintenance, one of the principles being considered is geomorphic design. This is based on the idea that while natural systems change over time, they are inherently stable. Their resilience is in stark contrast to many of the existing landscapes and watercourses developed by the resource industry, which have a tendency to fail and require repair and monitoring.
With resource companies seeking “walk-away closure,” or at least a way to minimize their ongoing monitoring and maintenance costs, an active area of research and development is around better design of post-closure environments. As well as in traditional hard-rock mining, these issues are being felt in oilsands reclamation and closure.
Traditionally, “structural” engineered watercourses tend to be more linear and rely on stone armour to control erosion. Over time, and perhaps when a larger-than-design storm occurs, the watercourses may fail, resulting in increased erosion and sedimentation in receiving streams. In some cases, such as in hard rock mines,
the sediment contains acids, salts, metals and other contaminants. There is little in the way of “self-healing” in these watercourses, meaning that work crews must be dispatched to repair the damage to the armouring.
Geomorphic watercourses, by contrast, use a variety of methods including sinuosity (meanders), riffles and pools to control erosion and create diverse aquatic habitat. It is important to understand that just as natural watercourses experience change over time, the goal of geomorphic design is not complete stability as it is with structural design, but rather dynamic stability. There may be erosion after a major storm, but there is long-term stability.
Geomorphic design involves understanding what designs work in nature, and then as much as practical, imitating those designs in engineered environments. The key is that while these environments are designed to imitate Mother Nature, it must be Mother Nature as she appears locally.
Natural watercourses evolve to meet a complex set of local factors including the underlying geology, precipitation patterns and topography. A watercourse with given characteristics including width, depth, sinuosity, riffle and pool size, roughness and other factors, which works well in one area, might not work as well elsewhere.
This is why geomorphic design involves up-front investment in researching local systems to determine their characteristics, with a view of replicating these characteristics in engineered watercourses in the reclaimed areas, located in the same region.
This research can be used in two ways – one being the “analogue” method, in which the characteristics of a nearby natural channel are replicated in a new location or reclamation area, based on comparable terrain, sediment transport and hydrology. The characteristics of the natural channel are recorded and used to guide the creation of a new stream.
In some circumstances, such as when no natural analogue stream can be found that meets the required criteria, a step-by-step process must be followed in which empirical relationships based on local data for relevant key parameters – including channel width and depth, sinuosity, slope and bed-material size – are used to design streams with attributes like those found in that environment.
Geomorphic watercourse design is part of geomorphic landscape design, in which landforms are designed with characteristics similar to those naturally found in the area. This often includes curves rather than straight lines, slopes that are steeper at the tops of hills than at the bottom, so the topography follows an S-curve, and small hilltops with sharp rather than flat peaks, to prevent excessive ponding of water.
Geomorphic design may represent a new challenge, requiring more up-front research to find appropriate designs for watercourses in the specific area being discussed. Also, developing skills in designing these watercourses and then producing them on the ground with heavy equipment may take some time.
It helps if those doing this work understand why the work is important. Also, it may be necessary to allow some extra time and
budget for the inevitable learning curve to be completed.
It is also important to communicate that while there may be higher up-front costs in geomorphic design, the long-term payoff is significant and includes reduced ongoing costs for maintenance, as well as legal liability.
Benefit also comes through a less-stringent regulatory approval for geomorphic design. Alberta’s Energy and Resources Conservation Board, which regulates some aspects of oilsands development including the design of landforms in reclaimed areas, has indicated that geomorphic design meets its objectives regarding post-closure environments. Alberta Environment, which is responsible for sustainable-use water and land, and the federal Department of Fisheries and Oceans, in charge of sustainability of aquatic resources, also look favourably on the geomorphic design approach.
Implementing geomorphic design in the oilsands will take time, particularly with a typical mine development having a lifespan of over 20 years, and a size of 60 sq. km to 100 sq. km. Total E&P Canada, and its parent Total, believe that geomorphic approach for watercourses and landscape design is a positive step in reclaiming oilsands mined areas.
– Femi Ade, Ph.D., P.Eng., is a Senior Environmental Advisor (Water Lead) with Total E&P Canada, based in Calgary, Alta. Contact: email@example.com; Tel. +1 (403) 536-8110. This article is based on a workshop and paper to which the author will be contributing at the Mine Closure 2011 conference (www.mineclosure2011.com), to be held Sept. 18-21, 2011, in Lake Louise, Alta.
Field research guides stream design
France’s Total participated in a geomorphic research study conducted by the Environmental and Reclamation Research Group of Canadian Oilsands Network for Research and Development. This research involved a survey of a representative array of watercourses including a variety of creek sizes, upland and lowland streams, and creeks located in a variety of geological conditions. This was necessary for understanding and characterizing natural alluvial channels in the oilsands region (OSR), so they could be replicated as part of mine closure.
Over two years, detailed geomorphic surveys were conducted at 54 representative stream reaches to collect channel dimensions, channel slope, sinuosity, bed material composition and instantaneous discharge. This dataset was augmented with data available in oilsands environmental reports and regional maps, and flow modelling results of the selected stream reaches and their basins.
The resulting dataset was used to produce region-specific regime relationships relating reach-averaged channel parameters for width, depth and slope to discharge. Relationships were provided to reflect the variations in channel variable within a reach, and recommendations were provided for meander wavelength and meander belt width.
Roughness caused by large wooden debris and other obstructions such as active and inactive beaver dams was found to have a significant effect on channel morphology. This effect can be mimicked, prior to beaver colonization, by placing roughness elements across the constructed channels at specified intervals using a design tool developed for this purpose.
A step-by-step design procedure for replicating natural analogues or using the regime approach is provided to as
sist in designing alluvial channels in OSR mine closure landscape. The research results have been used in the conceptual closure drainage designs for a number of Oilsands mine developments, including Total’s Joslyn North mine.