TECHNIQUES FOR CREATING MINING LANDFORMS WITH NATURAL APPEARANCE

Transcription

1 Reprint TECHNIQUES FOR CREATING MINING LANDFORMS WITH NATURAL APPEARANCE Gord McKenna Senior Geotechnical Engineer BGC Engineering, Vancouver Tailings and Mine Waste 09 Banff 2009 Gord McKenna, PhD, PEng, PGeol Senior Geotechnical Engineer # Howe Street Vancouver, BC V4K4S4 Canada or Phone Citation: McKenna, G. (2009) Techniques for creating mining landforms with natural appearance, Proceedings of Tailings and Mine Waste 09 Conference. Banff, Alberta. November 1 4, The University of Alberta Geotechnical Centre, Edmonton.

2 TECHNIQUES FOR CREATING MINING LANDFORMS WITH NATURAL APPEARANCE Gord McKenna, Senior Geotechnical Engineer BGC Engineering, Vancouver ABSTRACT Building on the successes of mine reclamation, some mining companies, regulatory agencies, and stakeholders are starting to require that reclaimed mining landscapes and mining landforms have a more natural appearance. At present, there is little guidance on meeting this new requirement. While most stakeholders aren t clear just what they want, they are often vocal in expressing what they don t want monuments to mining such as terraced pyramid-like waste rock dumps, long linear drainage ditches, peneplain plateaus, trees planted in straight lines ( plants on parade ), rectangular ponds, and flume-like wetlands. Fortunately several strategies and tools are available to designers and operators to create reclaimed landscapes that better meet society s expectations for natural appearance. One such approach, landform design, offers a more holistic approach to design of mining landscapes that incorporates a variety of specialists including geotechnical, surface water, groundwater, soils, vegetation, and wildlife. The landform design toolkit includes tools like landform grading, use of natural analogs, terrain analysis for anthropogenic landscapes and new surface water design and construction techniques that result in more sustainable landscapes that more closely resemble natural ones ideally where form follows function. One tool is a cafeteria-style list of elements that can be incorporated into reclamation designs. Many of these elements are simple and costeffective to incorporate into designs and help to provide greater landscape diversity and variety and contribute to breaking up some of the linear and planar patterns inherent in mining activities. Architectural rendering techniques are being applied in the design stages to get stakeholder buy in and to better answer the question up front, Will the reclaimed landscape be natural-looking? Designers and operators need to remain vigilant that the proposed changes to designs and construction techniques do not adversely affect environmental performance (and in particular, geotechnical stability) for the sake of aesthetics. Methods, tools, and examples of successful projects are included in this paper. INTRODUCTION The notion of designing mining landscapes to be aesthetically pleasing is somewhat troubling to many miners. Perhaps it is because mine design involves constraints and trade-offs and is ultimately a compromise of performance and economics some may feel that including aesthetics means compromising on performance or cost or perhaps that it goes against the effective spartan business demeanor of many miners. Talking about industrial design, Gelernter (1997) notes that to pay money for elegant technology is to seem unserious, selfindulgent, and arguably incompetent. Perhaps concern about agreeing to create naturallooking landscapes relates to a lack of direction and experience. And while beauty is in the eye of the beholder, there is a general trend for regulators and stakeholders to ask (or require) mines to produce reclaimed landscapes that are more natural-looking to reduce the use of straight lines and planar slopes, to use native species for revegetation with trees and shrubs planted in less regular patterns and in patches of size and shape that mimic the surrounding terrain. Discussion of natural appearance is often framed in terms of visual aesthetics. Related experiences, such as auditory or olfactory aesthetics may also be important or implied. This paper minces the terms natural appearance and aesthetics, and thus overlooks the fact that an elegant concrete arch dam can have high visual appeal, very strong aesthetic appeal, but rather unnatural appearance. Rolston

3 (1998) and especially Cronon (1995) provide good philosophical discussions of our historic and modern meaning of the words nature and natural and explore the implications for policy and decision making that are important to understanding such topics as environmental protection, mine reclamation, and have bearing on the present topic. This paper provides some background to the issue, discusses the need for a more holistic and multidisciplinary approach to landform design, and more practically provides a cafeteria-style list of landform design elements that can be employed to make mining landforms have a more natural appearance. Most of these elements are also useful in creating habitat and diversity in the landscape embodying the idea of form follows function from architecture and industrial design. Learnings that went into this paper are largely based on hands-on experience at two large oil sands mines in northern Alberta (Syncrude Canada and Suncor Energy), and reclamation tours at about 100 mines in North America, Australia, and Europe. The author has been influenced by numerous colleagues, notably Horst Schor of HJ Schor Consulting, Les Sawatsky of Golder Associates, Marie Keys of Syncrude Canada, Andy Robertson of Robertson Geoconsultants, and Professors Dave Sego and Nordie Morgenstern of the University of Alberta. Artwork in this paper is provided by provided by Derrill Shuttleworth of Studio Two in Edmonton. STATE OF PRACTICE Most mining landforms (dumps, dykes, tailings ponds, channels, open pits) are designed for geotechnical stability and efficiency of construction (McKenna, 2002). They usually consist of rectangular shapes, evenly-spaced benches (terraces) with linear crests and toes, with angleof-repose slopes between them, and constant elevation crests (peneplains). Reclamation involves regrading the intermediate slopes between the berms to constant planar slopes (say 2H:1V or 4H:1V), smoothing out any irregularities, covering with constant thicknesses of soil, and planting vegetation at constant densities (stems per hectare), often in long rows. Surface water drainage features, where employed, are usually retrofit during reclamation or afterwards, and consist of long, linear, trapezoidal channels, often of constant grade, often lined with uniform riprap. However, most mines have at least one location that breaks these rules. For example, a roughened and sculpted dump slope, rockpiles placed haphazardly on the landscape to provide rodent habitat, a wetland with a shallow irregular shoreline, a grove of shade trees, or a meander in a watercourse. Usually individuals (artisans) are responsible and take pride for these special areas. These areas are often featured in a mine s promotional materials. A few mines have adopted natural appearance criteria in the design of all new landforms. See Table 1 for examples of each. Table 1. Examples of mines using natural appearance Location Examples of elements employed *Anaheim residential, Landform grading CA Falconbridge, ON Preservation of historic areas Faro, YT Roughening Highland Valley Roughening, meandering creeks Copper, BC Island Copper, BC Sculptured shorelines, snags *Line Creek Coal, BC Dump roughing, sculpted coal waste piles *MiBrag Coal, Sculpted shorelines for pit lakes Germany Millennium Slash spread on reclaimed areas Chemicals, W. Aust. Molycorp, NM Angle of repose planting *Premier Coal, W. Sculpted beaches, natural Aus. revegetation planting *Price Coal, UT Slope roughening, diagonal swales SF Phosphate, UT Slash *Suncor, AB Landform grading, ridge mounds, irregularly shaped wetlands, native vegetation *Syncrude, AB Landform grading, roughening, ridge mounds, rockpiles, native vegetation *TransAlta Highvale, Landform grading, irregular AB ridgelines, tailored planting * indicates sites where most new landforms are designed to have natural appearance.

4 Why natural appearance? There are several reasons for trying to create mining landforms that have natural appearance: to meet promises made to stakeholders to meet regulatory requirements for public relations value to create diversity in the landscape which in turn promotes resiliency a useful element of landscape performance (Holling, 1973) to follow a mantra of form follows function a landscape that is design to exhibit similar landscape performance (function) as the natural environment ought to look natural too (form). access to read and redrill geotechnical instruments. Avoiding geotechnical instability. There may be instances where slopes that are marginally stable could be affected by changes in slope geometry any changes for the purposes of natural stability must honour the need for geotechnical (and erosional) stability. Often natural appearance and stability will go hand in hand, if done well. Hardrock pit walls. Most benched pitwalls are generally considered too expensive to reclaim and remain as unusual scenery. The idea that form follows function was coined by Sullivan (1896) while reflecting on the design of high-rise office buildings. Sullivan explains, It is the pervading law of all things organic and inorganic, of all things physical and metaphysical, of all things human and all things superhuman, of all true manifestations of the head, of the heart, of the soul, that the life is recognizable in its expression, that form ever follows function. Slightly more down to earth, Gelernter (1997) states, a useful object has a natural form which when it is in complete harmony with its function is perceived as having a special rightness or fit that borders on art its shape seems less designed than at long last discovered. And why not? There are cases where designers may chose to build landforms that don t have natural appearances: Non-natural land uses. While many mine landscapes are reclaimed back to natural areas for wildlife habitat or forestry, some are reclaimed to gardens, industrial areas, or held for later remining. In these cases, natural appearance may be undesirable. Preservation of historic resources. Miners are often proud of the pits and dumps they have constructed, and value their anthropogenic nature above hiding them with regrading and vegetation. Similarly, ruins of mining buildings are often preserved as historic facility as a reminder of a previous age. Ease of monitoring dams. In some cases, planar slopes with linear crests, with slopes simply grassed are easier to monitor that sculpted landforms with diverse swales and large trees. Similarly, flat benches provide Pitwalls are generally left unreclaimed Other objections include: too expensive (not usually the case), that beauty lies in the eye of the beholder (yes, but there is often general agreement on whether a particular design is acceptable), efforts would be unmeasurable (yes, though there have been attempts, doesn t show once trees have grown (often largely true, but can be considered in design), and people like the mining look (as some miners do), and that one will never be able to fool everyone (but this is not usually the intent). Trends Some regulatory agencies are mandating activities to improve aesthetics. This is accomplished by requiring mines to present closure plans showing what final reclamation will look like, and then requiring public approval for the plans. If the proposal does not meet the approval of stakeholders, the mine must adjust the plan. This is one mechanism to address the subjectiveness of aesthetics. Typically it is found that building for natural appearance has the same cost as traditional reclamation, can be done with medium

5 to large equipment, and is usually simpler than traditional reclamation. Results are always appealing to stakeholders and regulators, staff and management. Thus the trend is for more and more sites to desire or require design and construction for a more natural appearance and the need to defend traditional approaches in some situations. Open vistas High, steep terrain Colourful terrain Open water and rivers, especially clear water Exposed bedrock, riverbanks Rapids, falls Rare or scarce scenery Historic features It is perhaps ironic that unreclaimed mining landforms and landscape will often score quite high in quantitative visual appeal systems, especially when they offer scarce historic scenery in otherwise natural areas. In contrast, a mining landscape that is reclaimed to have a natural appearance will often be indistinguishable from natural landscapes to the casual observer, particularly in forested regions. Time to move the goalposts again! ASSESSING NATURAL APPEARANCE There have been numerous attempts to score natural appearance systematically and quantitatively. The literature offers guidance for those interested. Among the more famous, Leopold (1969a,b) developed a system for rating natural appearance of river valleys using 46 factors in three broad categories (physical factors, biologic and water quality factors, and human use and interest factors) and rated these factors on a scale of 1 to 5. See also Carlson (1977), Litton et al., (1974) and Wilson-Hodges (1978) for other systems. Quantifying visual appearances has been examined for other industries. For example, highway engineering, transmission lines, quarries, barriers and walls, and cell phone towers. While much of the effort is directed towards halting proposed projects or litigation with respect to real estate values being degraded, the literature offers advice on public perceptions and provides landform designers with useful design information. Much of the most useful information for miners is available in methods and tools of mitigating visual impacts of logging (e.g. British Columbia Ministry of Forests, 1995). Items that score highly in some of these schemes include: Because most people know what they don t want, and aesthetics is highly personal and cultural, the author has found it more useful to take a qualitative approach using visual aids to communicate what the landscape will look like when reclaimed and seek input from stakeholders and regulators. Accepting input, and making changes, usually leads to acceptance of plans, with a new onus on the miners to deliver what is promised. Such a system forms the basis for approval of municipal developments architectural renderings of the proposed designs are presented, modified, and if approved, the owner is responsible to live up to the presentation. Renderings of often done in watercolours, or three-dimensional models, or more recently computer-generated artwork. The mining industry uses all of these approaches, but inconsistently. DESIGN AND CONSTRUCTION APPROACHES There are several approaches to creating landscapes with natural appearances. Artisan approach At most mines, there are one or more individuals (often biologists, reclamation specialists, or heavy equipment operators) that create areas in the reclaimed landscape that are natural-looking and have high aesthetic appeal for most visitors and staff. Examples are provided in Table 1. These examples tend to be one-off approaches to a few areas of the mine site. Many are done under the

6 radar. Some win awards. These approaches can be effective, sometimes costly, but are difficult to apply at the landscape level (in other words, across the whole minesite). Landform design If we argue that to achieve a natural appearance that involves aspects of geotechnical, surface water, groundwater, soils, vegetation and wildlife, a multidisciplinary approach is needed. In many cases, the integration of surface water drainage into the design of dumps and dykes and their associated plateaus, along with the use of revegetation species found in the local environment and planted logically (moisture-loving plants in the swales, plants that tolerate drier conditions on the ridges) following ecosite patterns similar to the natural environment, will produce largely natural-looking landscapes as an output of the design (rather than an explicit input). Landform grading The multidisciplinary landform design team Landform design (McKenna, 2002) is one such approach to the design and construction of mining landscapes. Beyond the specialists listed above, it also involves mine planners and operations people and other specialists. The focus is on setting clear, simple, and achievable landscape performance goals, then involving designers, planners, managers, and operators to build landscapes that can be reasonably expected to meet these goals. This paper argues that one of the goals that deserves to be considered is natural appearance. Landform grading was invented by Horst Schor a generation ago and is applied to various large residential and mining projects (Schor and Gray, 1995; Schor and Gray, 2007). Landform grading attempts to mimic stable natural hillslopes and involves shaping slopes to have natural geomorphic patterns (swales and ridges) that fit with the local geography and climate, supported by vegetation compatible with slope hydrogeology. Landform grading has been extended in the oil sands region to also include dump plateaus and tailings beaches, shaping these otherwise nearly flat and planar features to having nested watersheds and drainage patterns to support the local land uses, vegetation, surficial hydrology and groundwater hydrology. Landform grading is one of the major tools employed by landform design teams. Experience has shown landform grading to be practical and indistinguishable in cost from conventional grading. It results in mining landforms that have natural appearance and landscape performance that is similar to the natural surrounding environment. Landform design draws heavily on practical mine reclamation experience, but also brings to bear such disciplines as geomorphology, soil science, wildlife science. The use of natural analogs (Keys et al., 1995) is an important design tool the idea is to design mine plateaus, slopes, and streams to mimic natural features in the region, arguing that the natural features are products of the local materials, climate, and processes over thousands of years. This formal approach to the design of landforms and landscapes offers transparent and integrated efforts, drawing on the weight of the engineering design approach and the knowledge and creativity of a wide variety of specialists. Landform grading includes sculpting slopes into microwatersheds using swales and ridges. Landform grading applied to civil project often required very tight survey control and extensive

7 monitoring and sign-off. In a mining environment, there is more flexibility; much of the finer features (swales, ridges, planting schemes, etc) can be (and should be) field fit by a qualified field supervisor and conscientious operators. While the field construction costs are typically no higher with landform grading, the level of engineering design can be about double that of conventional design, but still a tiny fraction of the project cost. Landform grading of a small mine dump DESIGN ELEMENTS Table 2 provides design elements that can be used as a cafeteria-style list for the design of landforms with natural appearance. Some typical dimensions are provided. All elements need design (either in the office or the field) by qualified individuals and signoff that regulations will be met, geotechnical stability is assured, and that the elements will work well together to provide the promised landscape performance. Table 2. List of landform design elements for natural appearance Item Example 1. Meandering Irregular m wavelength, creek Minimum amplitude = 1 to 2 2. Connect swales with natural watercourses 3. Coversoil and revegetate bare areas, creek widths Drain swales into adjacent watercourses. Carry vegetation patterns from natural gullies up onto the dyke or dump slopes. Opportunity for aggressive reclamation of exposed areas near roads and creek slopes Item creeks 4. Watershed berm at crest 5. Irregular ridge mounds 6. Reslope benches 7. Wetlands at toes 8. Tailored planting 9. Swales on slopes Example allow early reclamation and general greening up of area. Push up dump material and round the downstream crest as final design feature. Horizontal wavelength 200 to 400 m, zigzag 0 to 20 m, vertical height 2 to 4 m, 2.5 to 4H:1V sideslopes with 3 to 5 m crest width Australians call these bunds. They can be built by using large mining trucks and later shaping the resulting line of spoil piles. To add diversity to skyline profile, add irregularly shaped mounds at the downstream crest Mounds can be 3 to 5 m high, 3H:1V sideslopes or flatter, 20-30m wide, 30-80m long (2000 to 10,000 m 3 each) Consider planting schemes to enhance appearance. Mound heights should be designed to be 5-15% of the landform height to break up sightlines. Mounds can be placed near the crest acting like false storefronts in a Western town. When finished with benches, reslope by regrading substrate or adding additional reclamation material. Make sure that access to place reclamation material is left. Enlarge toe ditch (toe creeks!) to create shallow wetland, 2 m deeper than toe ditch invert (where ditch invert is shallow) Consider m wide, 30 to 60 m long ( m 3 ) Use irregular shoreline, very shallow slopes, create mounds with spoil Follow ecosite planting schemes tailor the planting to fit conditions Consider planting swaths of trees for visual patterns on slopes Use this scheme to mimic natural vegetation patterns elsewhere Construct swales and ridges of slopes to carry runoff safely to the toes of dumps. Use diagonal, elbow, and curvilinear shapes. Hydrologic design required above threshold watershed

8 Item 10. Reclaim erosional fans and gullies in place 11. Irregular shoreline Example areas and slope gradients. Once gullies are stabilized, instead of erasing them, simply repair them in place Allows increased diversity, reduced cost Need to remove the cause of the gully prior to fixup in most cases Irregular shoreline should be integrated with construction for lakes, wetlands, marshes, and fens. 12. Littoral zone Build large littoral zones (typically less than 2m deep) into design of lakes 13. Add additional fill at toe 14. Mounds on plateaus, benches, slopes 15. Brushpiles / snags Adding fill at toe to break up straight lines and add topographic diversity may be desired Similar effect achieved by reclaiming erosion fans in place Expensive if not a short haul / short overhaul Small mounds on berms and slopes for topographic diversity Can be pushed up or placed or cut/fill from other projects Typically m diameter, 3-5 m high ( m 3 ) Field fit where practical. Temporary habitat improvements can be made by having small brush piles for small animals or standing snags for raptors 16. Rockpiles Build rock piles from siltstone for animal habitat 6 to 15 m diameter, 2 to 4 m high 17. LFH placement 18. Microtopogra phy 19. Coversoil diversity 20. Access controls 21. Viewing platforms / Place forest floor salvage in islands to promote early biodiversity Slash (coarse woody debris) also enhances diversity and habitat. Roughen slope to create microtopography to enhance soil moisture and diversity Use different prescriptions in different areas to enhance diversity Establish a plan for long-term access to area Provide good access, but restrict number of roads and type Use aesthetic design principles from trail guides to guide designs. Install viewing platforms for tours and future recreational Item photo locations FINAL COMMENTS Example opportunities. Creating natural-looking mining landforms and mining landscapes is a creative challenge. Successful reclamation of these landscapes will involve a multidisciplinary team using a variety of design tools and analyses. The results are rewarding personally, for the team, the mining company, and society. Formal design processes are needed for many elements to avoid triggering unintended consequences and for managing costs. Ideally form will follow function, and the landscapes will be both more visually appealing and exhibit better landscape performance. REFERENCES British Columbia Ministry of Forests, Visual impact assessment guidebook, British Columbia Ministry of Forests, Victoria, BC. Carlson, A.A., On the possibility of quantifying scenic beauty. Landscape Planning, 4: Cronon, W. (Editor), Uncommon ground: toward reinventing nature. W.W. Norton & Co., New York, 561p. Gelernter, D.H., Machine beauty: elegance and the heart of technology. MasterMinds. Basic Books, New York, 166p. Holling, C.S., Resilience and stability of ecological systems. Annual Review of Ecology and Systematics, 4: Keys, M.J., McKenna, G., Sawatsky, L. and Van Meer, T., Natural analogs for sustainable reclamation landscape design at Syncrude. In: COGEMA Resources Inc (Editor), Environmental Management for Mining, Saskatoon. Leopold, L.B., 1969a. Landscape esthestics: how to quantify the scenics of a river valley. Natural History(October): Leopold, L.B., 1969b. Quantitative comparison of some aesthetic factors among rivers, U. S. Geological Survey, Reston, VA, United States. Litton, R.B., Tetlow, R.J., Sorensen, J. and Beatty, R.A., Water and landscape: an aesthetic

9 overview of the role of water in the landscape. Water Information Center, 314p. Rolston, H., Technology versus nature: what is natural? Journal of the University of Aberdeen Centre for Philosophy Technology and Society, 2(2). Schor, H.J. and Gray, D.H., Landform grading and slope evolution. Journal of Geotechnical Engineering, 121(10): Schor, H.J. and Gray, D.H., Landforming: an environmental approach to hillside development, mine reclamation and watershed restoration. John Wiley & Sons, Hoboken, NJ. 354p. Sullivan, L.H., The Tall Office Building Artistically Considered, Lippincott's Magazine. Wilson-Hodges, C., The measurement of landscape aesthetics. Working paper - Institute for Environmental Studies, University of Toronto ; no. 2. University of Toronto, Institute of Environmental Studies, Toronto, 52p