Slobodan B. Mickovski

Ecological mitigation of hillslope instability: ten key issues facing researchers and practitioners

BackgroundPlants alter their environment in a number of ways. With correct management, plant communities can positively impact soil degradation processes such as surface erosion and shallow landslides. However, there are major gaps in our understanding of physical and ecological processes on hillslopes, and the application of research to restoration and engineering projects.ScopeTo identify the key issues of concern to researchers and practitioners involved in designing and implementing projects to mitigate hillslope instability, we organized a discussion during the Third International Conference on Soil Bio- and Eco-Engineering: The Use of Vegetation to Improve Slope Stability, Vancouver, Canada, July 2012. The facilitators asked delegates to answer three questions: (i) what do practitioners need from science? (ii) what are some of the key knowledge gaps? (iii) what ideas do you have for future collaborative research projects between practitioners and researchers? From this discussion, ten key issues were identified, considered as the kernel of future studies concerning the impact of vegetation on slope stability and erosion processes. Each issue is described and a discussion at the end of this paper addresses how we can augment the use of ecological engineering techniques for mitigating slope instability.ConclusionsWe show that through fundamental and applied research in related fields (e.g., soil formation and biogeochemistry, hydrology and microbial ecology), reliable data can be obtained for use by practitioners seeking adapted solutions for a given site. Through fieldwork, accessible databases, modelling and collaborative projects, awareness and acceptance of the use of plant material in slope restoration projects should increase significantly, particularly in the civil and geotechnical communities.

How vegetation reinforces soil on slopes

Once the instability process e.g. erosion or landslides has been identified on a slope, the type of vegetation to best reinforce the soil can then be determined. Plants improve slope stability through changes in mechanical and hydrological properties of the root-soil matrix. The architecture of a plants root system will influence strongly these reinforcing properties. We explain how root morphology and biomechanics changes between species. An overview of vegetation effects on slope hydrology is given, along with an update on the use of models to predict the influence of vegetation on mechanical and hydrological properties of soil on slopes. In conclusion, the optimal root system types for improving slope stability are suggested.

Root morphology and effects on soil reinforcement and slope stability of young vetiver ( Vetiveria zizanioides ) plants grown in semi-arid climate

Currently used in many countries in the world, vetiver grass (Vetiveria zizanioides) applications include soil and water conservation systems in agricultural environment, slope stabilization, mine rehabilitation, contaminated soil and saline land remediation, as well as wastewater treatment. The root system morphology of vetiver was investigated in a small plantation growing on abandoned marl terraces in southern Spain. Root distribution with depth, laterally from the plant, as well as root parameters such as root diameter and tensile strength were also investigated. The profile wall method combined with the block excavation showed that the vetiver grass grows numerous positively gravitropic roots of more or less uniform diameter. These were generally distributed in the uppermost soil horizon closer to the culm base. In situ shear test on blocks of soil permeated with vetiver roots were carried out and showed a greater shear strength resistance than the samples of non vegetated soil. The root reinforcement measured in situ was comparable to the one predicted by the perpendicular root reinforcement model. The stability of a modelled terraced slope planted with vetiver was marginally greater than the one of a non-vegetated slope. A local instability on one terrace can have a detrimental effect on the overall stability of the terraced slope.

Resistance of simple plant root systems to uplift loads

Plant root systems frequently permeate both natural and engineered soil slopes, influencing slope stability via mechanical reinforcement and soil drying. These root systems are often loaded by external forces during slope movements and when plant stems are subject to animal foraging or wind gusts. A series of physical model tests were conducted to examine how root geometries, root properties, and soil effective stress states affect the pullout capacity of simple unbranched model roots. Lengths of wood, rubber, and real roots were pulled from dry and partially saturated sand. The tests revealed the importance of the root to soil stiffness ratio during progressive failure, the mechanical properties of soil (and interfaces) at low effective stresses, the root diameter, and the tortuosity of the root material. Scaling issues due to shear banding are more important, and effective stresses under wet conditions are smaller than in conventional geotechnical practice because roots have a relatively small diameter ...

Uprooting resistance of vetiver grass (Vetiveria zizanioides)

Vetiver grass (Vetiveria zizanioides), also known as Chrysopogon zizanioides, is a graminaceous plant native to tropical and subtropical India. The southern cultivar is sterile; it flowers but sets no seeds. It is a densely tufted, perennial grass that is considered sterile outside its natural habitat. It grows 0.5‐1.5 m high, stiff stems in large clumps from a much branched root stock. The roots of vetiver grass are fibrous and reported to reach depths up to 3 m thus being able to stabilise the soil and its use for this purpose is promoted by the World Bank. Uprooting tests were carried out on vetiver grass in Spain in order to ascertain the resistance the root system can provide when torrential runoffs and sediments are trying to uproot the plant. Uprooting resistance of each plant was correlated to the shoot and root morphological characteristics. In order to investigate any differences between root morphology of vetiver grass in its native habitat reported in the literature, and the one planted in a sub-humid environment in Spain, excavation techniques were used to show root distribution in the soil. Results show that vetiver grass possesses the root strength to withstand torrential runoff. Planted in rows along the contours, it may act as a barrier to the movement of both water and soil. However, the establishment of the vetiver lags behind the reported rates in its native tropical environment due to adverse climatic conditions in the Mediterranean. This arrested development is the main limitation to the use of vetiver in these environments although its root strength is more than suffcient.

A Decision Support System for the Evaluation of Eco-engineering Strategies for Slope Protection

A decision support system (DSS) has been developed to assist expert and non-expert users in the evaluation and selection of eco-engineering strategies for slope protection. This DSS combines a qualitative hazard assessment of erosion and mass movements with a detailed catalogue of eco-engineering strategies for slope protection of which the suitability is evaluated in relation to the data entered. The slope decision support system (SDSS) is a knowledge based DSS in which knowledge is stored in frames containing rules that can evaluate the available information for a project, stored as project specific information (PSI) in a data file. The advantages of such a system are that it accepts incomplete information and that the qualitative nature of the information does not instil the user with a sense of unjustified exactitude. By its multidisciplinary and progressive nature, the DSS will be of value during the initial stages of an eco-engineering project when data collection and the potential of different eco-engineering strategies are considered. The accent of the output of the DSS is on the application of eco-engineering strategies for slope protection as an environmentally-friendly solution aiding sustainable development. For its acceptance within the engineering community, the DSS needs to prove its predictive capacity. Therefore, its performance has been benchmarked against successful and unsuccessful cases of slope stabilisation using eco-engineering. The target audience and the areas of application of this DSS are reviewed and the strategies for further development in this area suggested.

Shallow landslides as drivers for slope ecosystem evolution and biophysical diversity

Shallow landslides may be seen as local disturbances that foster the evolution of slope landscapes as part of their self-regulating capacity. Gaining insight into how slope ecosystems function and evolve could make eco-engineering interventions on slopes more successful. The objective of the present study is to detect traits of shallow landslide-triggered ecosystem evolution, self-regulation and biophysical diversity in a small-scale landslide-prone slope in Northeast Scotland. A protocol was defined to explore the emergence of landslide-driven slope habitats. This protocol studied plant diversity, species richness and plant biomass differences and their interactions with certain soil and topographic attributes at three slope strata during two consecutive growing seasons following an assemblage of shallow landslide events. Plant species and soil properties with potential as indicators of the different landslide-driven slope habitats and landscape evolution were also considered. Shallow landslides contributed to biophysical diversity and created distinct slope habitats within the landscape. Habitat differences in terms of species richness and composition were a direct consequence of the slope self-regulation. Certain plant species were found to be valid indicators of landslide-driven biophysical diversity. Soil total nitrogen and resistance to penetration were related to slope habitat and landscape evolution. As expected, plant establishment relied upon light and nitrogen trade-offs, which in turn were influenced by landscape topography. The insights derived from this study will be useful in slope restoration, particularly in harmonising effective actions with the functioning of landslide-prone ecosystems. Further research directions to clarify the observed variability and interactions are highlighted.

Systems engineering approach to design and modelling of smart cities

A city is a very complex area with complex governing bodies and a number of decision makers. More often, cities are engines of economic development and are attractive places for people seeking employment and better quality of living [1]. As a consequence, cities are now facing a growing urban population which imposes stresses on urban quality of life and the environment. Among the major challenges faced by cities around the world, urban population growth is at the forefront as it is expected that future cities will be home for more than 70% of the global population by 2050. Other associated challenges include traffic congestion, environmental degradation, security, level of quality of public services, and effective resources management. To ensure sustainable development of cities with such a boom of urbanisation, cities around the world are embracing technology and adopting smart cities concept following the recorded development of information and communication technologies and internet of things. However, the literature [2] shows that the concept of smart cities is not being approached efficiently. A smart city is a system of subsystems and should be approached as a whole as opposed to infusing technology into subsystems one by one. To achieve this, there is a requirement of a standard platform to integrate all the subsystems of a smart city system. This work proposes a holistic model which integrates all the subsystems of a smart city system. The proposed model is based on systems engineering approach and Systems Engineering Modelling Language (SysML) is adapted as a potential modelling language. It is a general purpose visual modelling language for Systems Engineering applications and for complex systems such as smart cities and can handle better complexity and challenges such as documentation, communication, and management.

Hazard Assessment of Vegetated Slopes

The hazard assessment of vegetated slopes are reviewed and discussed in terms of the stability of the slope both with and without vegetation, soil erosion and the stability of the vegetated slope from windthrow and snow loading. Slope stability can be determined by using either limit equilibrium or finite element stability analysis methods. The limit equilibrium methods are extended to incorporate the vegetation parameters that are important for the stability of a vegetated slope. The factors that contribute to soil erosion are reviewed and the techniques for assessing and measuring the rate of soil erosion are presented. The assessment of windthrow hazards are comprehensively discussed and a mechanistic model called ForestGALES is introduced which has flexibility for testing many different forest management scenarios. The hazards presented by snow loading on forested slopes are briefly reviewed.

Soil and water bioengineering: Practice and research needs for reconciling natural hazard control and ecological restoration

Soil and water bioengineering is a technology that encourages scientists and practitioners to combine their knowledge and skills in the management of ecosystems with a common goal to maximize benefits to both man and the natural environment. It involves techniques that use plants as living building materials, for: (i) natural hazard control (e.g., soil erosion, torrential floods and landslides) and (ii) ecological restoration or nature-based re-introduction of species on degraded lands, river embankments, and disturbed environments. For a bioengineering project to be successful, engineers are required to highlight all the potential benefits and ecosystem services by documenting the technical, ecological, economic and social values. The novel approaches used by bioengineers raise questions for researchers and necessitate innovation from practitioners to design bioengineering concepts and techniques. Our objective in this paper, therefore, is to highlight the practice and research needs in soil and water bioengineering for reconciling natural hazard control and ecological restoration. Firstly, we review the definition and development of bioengineering technology, while stressing issues concerning the design, implementation, and monitoring of bioengineering actions. Secondly, we highlight the need to reconcile natural hazard control and ecological restoration by posing novel practice and research questions.