Mine landform design using natural analogues

Current practice for landscape reconstruction following opencast mining relies on topographic reconstruction, adaptive land management and botanical characterisation. Environmental processes may be altered where reconstructed landforms have significant relief. Consequently, environmental outcomes in cases where there is large scale land forming are unpredictable. Moreover, landscape restoration lacks an integrated methodology, and while many mine closures have detailed ecosystem and biodiversity objectives based on natural analogue areas there has been no reliable way to design these objectives into mine landforms. The methods used in landscape restorations to describe reference conditions are based on generalised environmental factors using regional information and incorporating conceptual models. Such models lack the precision and accuracy required to understand and restore hillslope environmental pattern at mine sites. However, methodological integration and statistical inference models underpinning the spatial inference methods in conservation and landscape ecology, and pedology may be applied to solve this problem. These inference models utilise digital terrain models as the core environmental data incorporating ecological theory to predict biodiversity and species distribution. Also, numerical mass balance models such as water and solute balance, which have been applied to understand environmental processes in landscapes, can be used to assess mine landform design. The objective of the work reported here was to investigate environmental variation, with sufficient accuracy and precision, in natural landscapes to design mature mine landforms and to demonstrate the capacity to predict ecological outcomes. This would extend current best practice - designing mine landforms with predictable hydrological and geotechnical outcomes needed to protect off-site environmental conditions – to the on-site environment after closure. The specific aims of this thesis were to: (i) evaluate the predictability of ecosystems based on regional ecological mapping: (ii) develop and evaluate quantitative, site specific environmental mapping and natural analogue selection methodology; (iii) evaluate a trial final landform cover (reconstructed soil) using water balance, water chemistry monitoring; (iv) design and evaluate a conceptual mine landform through the assessment of environmental processes in natural analogue areas; and (v) make valid predictions of revegetation outcomes on the conceptual landform. In meeting these aims, links between ecological theory, landscape analysis and the current practice in mine landform design were identified. The first phase of the thesis involved environmental investigations and surveys of extensive savanna environments on the Tiwi Islands (7320 km-2) and similar environments in the vicinity of Ranger uranium mine (150 km-2) in northern Australia. This first phase, reported in Chapter 3, investigated the reliability of conceptual landscape models used in regional ecological mapping in predicting ecological patterns in terms of vegetation and soil. The Tiwi Islands was selected because of the relatively uniform parent material and its simplified climate. This allowed the study of physiographic control of soil and vegetation patterns. The results identified correlations between vegetation pattern and landform that were confounded by a subjective and complex land unit model of ecosystems. This investigation enabled the development methodological approach to analogue selection and ecological modelling at Ranger uranium mine – a site that will require a restoration approach so as to meet environmental closure objectives. The second phase is the methodological development – involving an initial reconnaissance, is presented in Chapter 4. This phase was aimed at selecting natural analogue areas for mined land restoration. Environmental pattern recognition involving classification, ordination and network analysis was implemented based on methods of conservation ecology. This led to quantitative landscape model to identify natural analogue areas and design ecosystem surveys. This quantitative landscape model incorporated a grid survey of vegetation and soil variation into a nearby analogue landform that matched the area of mine disturbance. This analogue landform encapsulates the entire ecosystem types observed on rocky substrates in the broader reconnaissance survey. The natural analogue selection incorporated a combination of digital terrain analysis and k-means clustering of primary and secondary terrain variables to classify habitat variation on hillslopes. Landscapes with similar extent to the mine landscape were identified from numerical similarity measures (Bray-Curtis) of fine grained habitat variation and summarised using a dendrogram. The range in hillslope ecosystem types were described from stratified environmental surveys of vegetation and soils along environmental gradients in selected analogue landforms. The results show that the mapped environmental factors in close correlation with water and sediment distribution were strongly associated with observed vegetation patterns in analogue areas at Ranger uranium mine. Environmental grain size and landform extent concepts were therefore introduced using landscape ecology theory to integrate different scales of environmental variation in a way that provides direct context with the area impacted by mining. Fine-grained environmental terrain attributes that describe runoff, erosion and sediment deposition were derived from a digital elevation model and classified using non-hierarchical multivariate methods to create a habitat class map. Patch analysis was used to aggregate this fine-grained environmental pattern into a grid that matched the scale of the mine landform. The objective was to identify landforms that were similar in extent to the reconstructed mine landscape. Ecosystem support depends on soil as well as geomorphic factors. An investigation into critical environmental processes, water balance and solute balance, on a waste rock landform at Ranger uranium mine is presented in Chapter 5 to characterise waste rock soils and investigate cover design options that affect environmental support. This involved monitoring of water balance of a reconstructed soil cover on a waste rock landform for four years and the solute loads for two years. A one dimensional water balance model was parameterised and run based on 21 years of rainfall records so as to assess the long-term effects of varying cover thickness and surface compactness on cover performance. The results show that the quality of runoff and seepage water did not improve substantially after two years as large amount of dissolved metal loads persisted. Also, tree roots interacted with the subsoil drainage-limiting layer at one metre below the land surface in just over two years - and thus altering the hydraulic properties of the layer. Further, the results of water balance simulations indicate that increasing the depth to, and thickness of, the drainage-limiting layer would reduce drainage flux. Increasing layer thickness could also limit tree root penetration. It was also found that surface compaction was the most effective means of limiting deep drainage, which contained high concentrations of dissolved metals. However, surface compaction creates an ecological desert. Therefore long-term rehabilitation of the cover will be required to allow water to infiltrate for it to be available for ecosystems. A cover that can store and release sufficient water to support native savanna eucalypt woodland may need to be three to five metres deep, including a drainage limiting layer at depth so as to slow vertical water movement and comprise a well graded mix of hard rock and weathered rock to provide water storage and erosion resistance. The resulting waste rock soils would be similar, morphologically to the gradational, gravelly soils found in natural analogue areas. The study then shifted from mined land back to a selected natural analogue landscape at Ranger mine in Chapter 6. The fine grained variation in terrain attributes is described to support a landform design that allowed for mine plan estimates of waste rock volumes and pit void volumes. A process of developing and evaluating the landform design was put forward, in the case of Ranger, that begins with key stakeholder consultation, followed by an independent scientific validation using published landform evolution and integrated, surface-groundwater water balance modelling. The natural analogue and draft final landforms were compared in terms of terrain attributes, landform evolution and eco-hydrological processes to identify where improvements could be required. The results of the independent design reviews are contained in confidential reports to Ranger mine and in conference proceedings that are referenced in Chapter 6. Independent validation will be a key element of an ecological landform design process and the application of published eco-hydrological and landform evolution models at the Ranger mine case study site are presented as an example of current best practice. Also, detailed assessment was made of environmental variation and soil and geomorphic range in the selected analogue landscape to support the landform design process with the mining department. Ecological modelling of the distributions of framework species in the reconstructed landscape is proposed as an additional assessment tool in this thesis to validate an ecological landform design methodology. To this end, a detailed environmental survey is presented in Chapter 6 of the soils and vegetation in a selected natural analogue area of Ranger mine to identify common and abundant plant species and their distribution in a similar landscape context to the mined land. This work supported ecological modelling of species distributions in reconstructed and natural landscapes in the following chapter. The results of species distribution models for reconstructed and natural landscapes at the Ranger mine site are reported in Chapter 7. The aim was to predict the distribution of common and abundant native woodland species across a landscape comprising a sculpted, post mining landform within a natural landscape. Species distribution models were developed from observations of species presence-absence at 102 sites in the grid survey of the natural analogue area that was reported in Chapter 6. Issues related to optimising predictor selection and the range of environmental support were investigated by introducing survey sites from the broad area reconnaissance survey reported in Chapter 4. Added to these are the published species abundance data from an independent regional biodiversity survey of rocky, well drained eucalypt woodlands, used as analogues of mined land. Plant species responses to continuous and discrete measures of environmental variation were then analysed using multivariate detrended correspondence analysis and canonical correspondence analysis to select independent variables and assess the relative merits of abundance versus presence absence observations of species. Then, generalised additive statistical methods were used to predict species distributions from primary and secondary terrain variables across the natural analogue area and a reconstructed post-mining landform. This analysis was completed with an assessment of the effect that survey support has on model formulation and accuracy. The scale of the mine landscape was found to provide important context for the stratified environmental surveys needed to support predictive modelling. Extending the geographic range of survey support did not improve model performance, while survey sites remote from the mine introduced some degree of spatial autocorrelation that could reduce the prediction accuracy of species distributions in the mine landscape. Further work is needed to address uncommon species or species with highly constrained environmental ranges and aspects of landform cover design and land management that affect woodland type and vigour. The combined studies reported in this thesis show that the predictability of mine land restorations is dependent on the landscape models used to characterise the natural analogue areas. It is demonstrated that conceptual ecological models developed for regional land resources survey, commonly used to select natural analogue areas, are subjective, complex and unreliable predictors of vegetation and soil patterns in hillslope environments at particular sites. It was recognised that environmental patterns are subject to terrain and hillslope environmental variation across an extensive areas. The landform model for selecting natural analogues was refined by introducing grain size and ecological extent concepts, used to describe ecological scale in landscape ecology, to address these effects. These refined concepts were adapted to define environmental variation in the context of natural analogue selection for mining restoration, rather than home range habitat conditions for native animals as was their original purpose. It is demonstrated here that the grain size and extent of environmental variation in the natural landscape can be used to select natural analogue landforms, develop ecological design criteria and design field surveys that support the capacity to predict the distributions of common and abundant woodland species in a reconstructed landscape. In conclusion, it is worth noting that an integrated ecological approach to landscape design can be applied to closure planning at mine sites where cultural and ecological objectives are critical to the success of the mine rehabilitation. Furthermore final landform trials could be used to support a restoration approach — providing an understanding of the interactions between critical physical and ecological processes in the soil layers and environmental processes at catchment scales. The accuracy of the inferences made is dependent on the understanding of hydrological processes in natural and constructed landforms. However, the natural analogue approach provides a clear landscape context for these trials. In a world where species extinction resulting from habitat loss is one of the most important global ecological issues, mine rehabilitation offers unique experimental opportunities to develop capability in ecosystem rehabilitation

Modelling sediment storage times in alluvial floodplains

Soil erosion rates are accelerating worldwide as climate change effects and human population pressures, including agricultural expansion, degrade the land surface. Fluvial systems transfer sediments from uplands to depositional landforms and basins downstream. However, only a fraction of eroded material will ultimately transfer to catchment outlets – a phenomenon termed, “the sediment delivery problem”. Thus, sediment fluxes to the coast are declining in many river catchments, as a result of storage behind dams and within landforms such as floodplains and alluvial terraces. Storage time allows us to measure the timescale of storage and removal of sediments from floodplains, which, given their spatial extent (8 x 105 to 2 x 106 km2 of all land area), are significant in interrupting the transmission of soil erosion fluxes downstream. While sediment storage times in alluvial floodplains have been quantified before, this thesis presents the first attempts to model the impacts of various environmental and experimental conditions on sediment storage behaviour using the CAESAR-Lisflood landscape evolution model. The thesis tests the following hypotheses: i) Removal rates from storage decline with increasing floodplain age; ii) the distribution of sediment storage times is sensitive to reach-specific characteristics, vegetation cover types and changes, changing river flows, and measurement frequency; and iii) a non-linear function can be fitted to the distribution and parameterised using readily quantifiable variables. A detailed literature review synthesised our current understanding of sediment storage times, including variables that have been quantified or hypothesised as possible controls. This culminated in a conceptual model of major controls and their interactions which was used to support the development of experiments tested in this thesis. A review of quantification techniques, including “black-box”, one-dimensional mass balance modelling approaches, and methods that calculate storage times directly from timings of geomorphic changes, justified adopting a landscape evolution modelling approach. CAESAR-Lisflood was applied to conduct this research, as it can simulate variable channel widths, divergent flow, and both braided and meandering planforms – capturing a wider range of channel-floodplain evolution processes than models previously used to simulate storage times. Ten 1 km-long reaches of river valleys from the north of England were used to calibrate the model, test the transferability of calibrated parameters, and verify the accuracy of simulated historical channel changes against mapped reconstructions. These simulations replicated mapped erosion, deposition and lateral migration rates reasonably well overall. Floodplain turnover times, estimated by extrapolating erosion rates, increased confidence that calibrated parameters were representative over longer timescales and revealed that all sediments stored in the floodplain would undergo exchange with the channel within 1000 years. Using CAESAR-Lisflood, an ensemble of 9 simulations, incorporating 3 of the 10 calibrated reaches and 3 vegetation cover scenarios (forest, grass and unvegetated) – each spanning 1000 years of river channel changes – was run. Together with measuring channel changes over four different frequencies (10, 20, 50 and 100 years), a total of 36 storage time distributions was modelled, with the age and storage times of floodplain sediments calculated from timings of deposition and erosion. This was done to test whether distributions were best fit by either an exponential or a heavy-tailed decay function, with the former indicating constant erosion rates over space and time, while the latter implies that removal rates from storage decay with increasing deposit age. As well as uniform vegetation conditions, a further 15 simulations, incorporating changes in vegetation cover or flow magnitudes over time, were run, to test how storage time dynamics respond to disturbance. This thesis demonstrates that sediment erosion rates decline with increasing floodplain age in most cases, with the strength of this relationship dependent on reach, floodplain erodibility and frequency of recorded measurements. A lognormal function can be fitted to distributions of sediment storage times in most cases, and it is possible to parameterise this function using the median storage time and measurement time-step. Coupling this storage time function with a model of stochastic sediment transport could generate predictions of decontamination times for a valley corridor enriched with polluted sediments (e.g. from mining). However, some environmental disturbances can be great enough to invalidate this storage time model – a challenge that merits further attention before application to practical environmental management contexts

Adapting to climate risks and extreme weather: guide for mining - minerals industry professionals

AbstractExtreme weather events in Australia over recent years have highlighted the costs for Australian mining and mineral processing operations of being under-prepared for adapting to climate risk. For example, the 2010/2011 Queensland floods closed or restricted production of about forty out of Queensland’s fifty coal mines costing more than $2 billion in lost production.Whilst mining and mineral professionals have experience with risk management and managing workplace health and safety, changes to patterns of extreme weather events and future climate impacts are unpredictable. Responding to these challenges requires planning and preparation for events that many people have never experienced before. With increasing investor and public concern for the impact of such events, this guide is aimed at assisting a wide range of mining and mineral industry professionals to incorporate planning and management of extreme weather events and impacts from climate change into pre-development, development and construction, mining and processing operations and post-mining phases. The guide should be read in conjunction with the research  final report which describes the research process for developing the guide and reflects on challenges and lessons for adaptation research from the project.The Institute for Sustainable Futures, University of Technology Sydney (UTS) led the development of the guide with input from the Centre for Mined Land Rehabilitation, University of Queensland and a Steering Committee from the Australasian Institute of Mining and Metallurgy’s Sustainability Committee and individual AusIMM members, who volunteered their time and experience. As the situation of every mining and mineral production operation is going to be different, this guide has been designed to provide general information about the nature of extreme weather events, and some specific examples of how unexpectedly severe flooding, storm, drought, high temperature and bushfire events have affected mining and mineral processing operations. A number of case studies used throughout the guide also illustrate the ways forward thinking operations have tackled dramatically changing climatic conditions.Each section of the guide outlines a range of direct and indirect impacts from a different type of extreme weather, and provides a starting point for identifying potential risks and adaptation options that can be applied in different situations. The impacts and adaptation sections provide guidance on putting the key steps into practice by detailing specific case examples of leading practice and how a risk management approach can be linked to adaptive planning. More information about specific aspects of extreme weather, planning and preparation for the risks presented by these events, and tools for undertaking climate related adaptation is provided in the ‘Additional Resources’ section

Modelling rock slope behaviour and evolution with reference to Northern Spain and Southern Jordan

The geomorphological behaviour of steep jointed rock slopes has been studied using distinct element computer models. In order to model steep slopes effectively, methodologies need to be combined from the studies of environmental modellers, geomorphologists and engineers. The distinct element method is ideal for the study of the development of jointed rock masses, where the failure is controlled by the nature of the discontinuities. Theoretical modelling identified that block size is a key control affecting the deformation of rock masses. Deformation of rock masses with smaller block assemblages is greater than for rock masses composed of larger block sizes. This is due to the increased magnitude of joint normal closure. Catastrophic failure is less likely in slopes with smaller block sizes because the shear strength is greater in a closely jointed rock mass. These slopes are more likely to undergo gradual deformations. Block-size effects are also responsible for influencing the failure mechanism of rock masses. As block size decreases, the magnitude of block rotation increases and the failure mechanism changes from sliding to toppling. The effect of slope scale on the deformation properties of the rock masses has also been investigated. Two field locations, the Picos de Europa mountains, northern Spain and Wadi Rum, southern Jordan, have been chosen to provide a link between the theoretical modelling and classic rock landforms which are controlled by the discontinuity geometry. Given the sporadic and infrequent occurrence of failure events at the field sites, a computer modelling approach has been adopted to analyse slope behaviour. In the Picos de Europa, slope deformations are deep-seated, with sliding and toppling being the dominant modes of failure. Much of the slope deformation in these mountains is a result of post-glacial rock-slope deformation. The sandstone inselbergs of Jordan show a range of morphologies from rounded hills to vertical cliffs. The morphology of the inselbergs is related to the intact rock strength; stronger Red lshrin sandstone forms vertical slopes, whereas the weaker Disi sandstone forms rounded domes. Jointing in the area is sub-vertical with horizontal bedding and computer simulations have shown that toppling is the dominant mode of failure in these inselbergs. Comparison of computer model output suggests that different failure mechanisms have distinct failure signatures. Catastrophic, deep-seated failures are characterised by a long period of acceleration as the failure propagates through the rock mass and infinite velocity is reached. Non-catastrophic slope movements, such as self-stabilising topples, are characterised by short periods of acceleration followed by small creep movements at a constant velocity. Computer modelling has indicated that scale effects do exist in the modelled rock masses from the Picos de Europa and particularly Wadi Rum. In areas where jointing is constant, the relative block size of the rock mass decreases as slope scale increases. The greater numbers of blocks along with greater in situ stresses influence the failure of the slope. Cosmogenic dating was used to temporally constrain UDEC model output and provide a better understanding of rock slope failure mechanisms in the Picos de Europa and Wadi Rum. Dating indicated delayed paraglacial adjustment was the triggering mechanism for slope failure in the Picos de Europa, whereas failures in Wadi Rum appeared to be closely linked with wetter climatic conditions

Torrent erosion in Lake District mountain catchments.

This thesis investigates torrent erosion in Lake District mountain catchments,Northern England. A nested research approach was used. Detailed investigations were undertaken at two case study sites (Iron Crag, Raise Beck) together with a survey of torrents across the Skiddaw and Helvellyn massifs. At Iron Crag an annual sediment budget was constructed by monitoring hillslope,channel and fan processes. Particle size characteristics of sediments, and the history of fan development were investigated. Results show channel and bank sediments are the main source of material supplied to the fan. Large rainfall events cause significant change in the channel, banks and fan. The impact of different meteorological conditions on sediment characteristics is complex, however a seasonal cycle of sediment production (winter) and exhaustion (autumn) exists. Historically, initial fan aggradation predates 36 BC, but a rapid phase of deposition began between 1200-1400 AD. Investigations at Raise Beck focussed on a flood that occurred in January 1995 and caused channel avulsion and shallow landsliding. This was reconstructed using a range of geomorphological and sedimentological evidence. Palaeohydrological methods give a discharge between 27- 74 in s-1. whereas as rainfall-runoff values range between 4-6 m3 s-1. The magnitude of the 1995 flood was smaller than two 19th Century events, but would still exceed the capacity of contemporary engineered channels. The regional survey considered the characteristics and importance of torrents,mountain streams, and debris flows; and provided a context for work at the case study sites. The case study sites are distinct members of the regional populations. Raise Beck being the largest (133 ha) and highest (858 m O. D. ); Iron Crag amongst the smallest (2.4 ha) and lowest (600 m O. D. ). Overall, torrents and hillslope debris flows are minor components of the landscape (aerially 2.1 % Helvellyn massif, 0.4 % Skiddaw massif). Sites are preferentially located in regard to altitude and slope.Debris flows are related to geological type. Large torrent floods are relatively rare and can be broadly related to regional flood episodes. Contemporary debris flow activity is of low magnitude and frequency