Federico Preti

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.

Modeling the hydrological and mechanical effect of roots on shallow landslides

This study proposes a new methodology for estimating the additional shear strength (or cohesion) exerted by vegetation roots on slope stability analysis within a coupled hydrological-stability model. The mechanical root cohesion is estimated within a Fiber Bundle Model framework that allows for the evaluation of the root strength as a function of stress-strain relationships of populations of fibers. The use of such model requires the knowledge of the root architecture. A branching topology model based on Leonardos rule is developed, providing an estimation of the amount of roots and the distribution of diameters with depth. The proposed methodology has been implemented into an existing distributed hydrological-stability model able to simulate the dynamics of factor of safety as a function of soil moisture dynamics. The model also accounts for the hydrological effects of vegetation, which reduces soil water content via root water uptake, thus increasing the stability. The entire methodology has been tested in a synthetic hillslope with two configurations of vegetation type, i.e. trees and shrubs, which have been compared to a configuration without vegetation. The vegetation has been characterized using roots data of two mediterranean plant species. The results demonstrate the capabilities of the topological model in accurately reproducing the observed root structure of the analyzed species. For the environmental setting modelled, the effects of root uptake might be more significant than the mechanical reinforcement; the additional resistance depends strictly on the vegetation root depth. Finally, for the simulated climatic environment, landslides are seasonal, in agreement with past observations. This article is protected by copyright. All rights reserved.

Advances in remote sensing of hydraulic roughness

Riparian vegetation plays a crucial role in affecting the floodplain hydraulic roughness, which in turn significantly influences the dynamics of flood waves. Systematic detection, identification and assessment of flow resistance factors using conventional field sampling is often unfeasible as these techniques are time-consuming and expensive. As in many other environmental monitoring problems, remote sensing may provide unprecedented mapping capabilities. In this article we present an overview focusing on the different methods that can be used to remotely derive floodplain hydraulic roughness. The overview is based on an extensive literature review on recent estimation techniques of riparian roughness using remote sensing data from different platforms. The outlined methods of floodplain roughness parameterization include: (1) classification-derived hydraulic roughness maps and (2) estimation of vegetation hydrodynamic properties. Possible directions for a multiscale analysis of riparian flow resistance are also described in a short section by focusing on the potential of data assimilation methods for the estimation of floodplain roughness. The literature reveals that many valuable remote-sensing techniques have been developed for riparian corridor parameterization. Methodologies based on the fusion of multispectral/temporal imagery with data of different origin, such as light detection and ranging (LiDAR) and radar/microwave, appear to be powerful tools for characterizing riparian ecosystems for hydraulic purposes.

Overland transport of nitrate: Algorithms validation

An efficient and integrated approach for the study of overland transport of nitrate during runoff can be achieved by coupling water quality automatic monitoring and distributed parameter modeling. A semi-distributed model, essentially based upon a spatial discretization of the territory into square cells and upon a schematization of the main hydrological processes of erosion, transformation and transport of the chemical substances, was set up. It performs the lumped analysis of overland transport of nitrate (for the elementary cell of spatial discretization or experimental plot scale) and the distributed analysis with routing to the outlet of the watershed. In the present work the mathematical algorithms and the validation of the model are presented.

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.

Soil Bioengineering Measures in Latin America: Authocthonal Cuttings Suitability

The variety of Soil bioengineering techniques usable for disaster mitigation, environmental restoration and poverty reduction is nowadays little known in developing countries. Research on authochtonal plants suitable for this kind of works is the essential first step for the divulgation of this discipline. The present paper is focused on this issue related to the realization of various typologies of Soil Bio-engineering works in the Humid tropic of Ecuador. Realizing live palisades alongside an unpaved road, an experimental plot was obtained by planting 100 cuttings of each of the following species: Brugmansia versicolor Lagerh (local common name: Guanto); Euphorbia cotinifolia L. (local common name: Lechoso); Malvaviscus penduliflorus DC. (local common name: Cucarda), Trichanthera gigantea (Humb. & Bonpl.) Nees (local common names: Nacedero, quiebrabarriga, inchabarriga).

BIOMASSA E GESTIONE DELLA VEGETAZIONE DI SPONDA: IL CASO DEL TORRENTE RIPOPOLO (LI) ( 1 )

L’obiettivo del lavoro e la valutazione delle potenzialita produttive, in termini di biomassa legnosa, della gestione di vegetazione ripariale attraverso un approccio essenzialmente colturale. Il caso di studio e stato individuato nel bacino del Torrente Ripopolo, nel comune di Suvereto (LI), all’interno del Parco Interprovinciale di Montioni. Sono state valutate le interazioni tra il soprassuolo e i deflussi idrici, proponendo interventi in accordo coi parametri morfologici, idraulici e vegetazionali. I risultati hanno consentito di valutare quantita e caratteristiche del materiale legnoso utilizzabile, nonche la periodicita degli interventi. Lo studio riflette le nuove concezioni in materia di difesa del territorio e gestione sostenibile delle risorse forestali attraverso una revisione critica delle metodologie tradizionali e giunge ad una visione multi-obbiettivo che, per sua definizione, non puo prescindere dalla componente idraulica.

Coupling Root Reinforcement and Subsurface Flow Modeling in Shallow Landslides Triggering Assessment

Vegetation significantly influences the hydrological and mechanical properties which are relevant for the stability of shallow soils along sloping surfaces. In view of the complexity of soil plant hydrological interactions, the quantification of root mechanical reinforcement remains a challenge. In this paper we couple root reinforcement models with a quasi-dynamic wetness index (QDI), which is specifically designed for estimating the local wetness conditions by accounting for the character of the upslope topography and the time of the lateral soil moisture distribution. The overall modelling strategy can be effectively employed for assessing the relative hazard of shallow landslides accounting for vegetation patterns and dominant forest management practices. The methodology is applied to an area located in Northern Tuscany, recently interested by several shallow landslides.

Experiences of improving water access in rural areas in Guatemala

The GESAAF Department of the UNIFI has been involved in the project “Gestione ambientale e del rischio nel dipartimento di Solola” in the period 2011-’12 aiming at guaranteeing water access to people leaving in rural areas in the Solola Department in Guatemala, in collaboration with the two NGOs Movimento Africa ’70 and Oxfam Italia. Appropriate technologies, such as EMAS pump and well drilled with the Baptista- Boliviana technique, have been proposed and utilized for improving water access in areas where lack of water represented a limiting factor for the human development. They can be both considered compatible with local, cultural and economic conditions: in fact locally available materials are used and the tools can be maintained and operationally controlled by the local users. At the end of the project, 52 EMAS pumps have been installed and 19 wells drilled, 33 pumps have been installed in already existing wells tank. Formation activities of local people played an important role: diffusion actions of the methodology started from schools, 20 workers participated to an in class course and more than 100 participated in the field work. Monitoring activities on the 52 installed pumps have been carried out in order to check the performances of the pumps and the knowledge level acquired by the users. After some months of operation, more than 80% of the pumps were correctly functioning and the required maintenance activities have been carried out in collaboration with the local users. In order to analyze the project results, a SWOT analysis (Strengths, Weaknesses, Opportunities, and Threats) has been carried out for developing a strategy able to tackle the weaknesses and threats of the procedure. The application of the SWOT analysis showed to be an useful tool to analyse the current situation coming from the ended project. It has been helpful to gauge how the project performed. The analysis results may be also utilized for exploring strengths and weaknesses of a possible transferring of the methodology to other sites.

Monitoring ground bio-engineering stabilization of landslides in Lazio Region, Italy

Latium, like most other Italian regions, is subject to numerous landslides and gravitational movements. These landslides have been registered and mapped by the Region of Latium. Sixteen sites were chosen for the monitoring of ground bio-engineering projects which are currently being carried out in collaboration between the Region of Latium and the GEMINI Department of the Tuscia-Viterbo University. The monitoring activity was performed by completing a questionnaire for each site. The main data required, in order to have a complete vision of the site and its problems, concerned descriptions of the morphological, lithological and phytoclimatic aspects of the slope. This information was provided by the planners and contractors, who also gave a description of the ground bio-engineering techniques used to stabilize landslides. The aim of this study was to verify the effectiveness of using ground bio-engineering techniques in the Mediterranean climatic zone. In this zone, rooting of plants is especially complicated, but we can exploit the biotechnical characteristics of plants and adapt ground bio-engineering methods to this area. We can use information from this study to protect the territory, whilst minimizing the environmental impact, thus fostering and protecting the environment in areas where ground bio-engineering is carried out.