Network Analysis, Creative System Modelling and Decision Support: The NetSyMoD Approach

This paper presents the NetSyMoD approach where NetSyMod stands for Network Analysis Creative System Modelling Decision Support. It represents the outcome of several years of research at FEEM in the field of natural resources management, environmental evaluation and decision-making, within the Natural Resources Management Research Programme. NetSyMoD is a flexible and comprehensive methodological framework, which uses a suite of support tools, aimed at facilitating the involvement of stakeholders or experts in decision-making processes. The main phases envisaged for the process are: (i) the identification of relevant actors, (ii) the analysis of social networks, (iii) the creative system modelling and modelling of the reality being considered (i.e. the local socio-economic and environmental system), and (iv) the analysis of alternative options available for the management of the specific case (e.g. alternative projects, plans, strategies). The strategies for participation are necessarily context-dependent, and thus not all the NetSyMod phases may be needed in every application. Furthermore, the practical solutions for their implementation may significantly differ from one case to another, depending not only on the context, but also on the available resources (human and financial). The various applications of NetSyMoD have nonetheless in common the same approach for problem analysis and communication within a group of actors, based upon the use of creative thinking techniques, the formalisation of human-environment relationships through the DPSIR framework, and the use of multi-criteria analysis through the mDSS software

Numerical modeling of the effect of preferential flow on hillslope hydrology and slope stability

The topic of this thesis is the quantification of the influence of preferential flow on landslide-triggering in potentially unstable slopes. Preferential flow paths (e.g., cracks, macropores, fissures, pipes, etc.) commonly exists in slopes. Flow velocities in preferential flow paths can be significantly larger than in the matrix. Under large rainfall or snow-melt events, preferential flow can bypass the adjacent soil matrix and directly reach the groundwater table. The fast pressure build-up caused by preferential flow can reduce the effective stress and shear strength, which is an important triggering factor for landslides. Single-permeability models can not appropriately simulate preferential flow. Hence, hydro-mechanical models of landslide need the inclusion of preferential flow. Preferential flow also affects tracer transport in subsurface flow systems. The celerity in unsaturated flow represents the maximum water velocity in a soil, and it may be used to predict the first arrival time of a conservative tracer. The celerity function is derived from the soil hydraulic conductivity function for unsaturated flow, and is used to derive the breakthrough curve of a conservative tracer under advective transport. Analysis of the bimodal hydraulic function for a dual-permeability model shows that different parameter sets may result in similar soil hydraulic conductivity behavior, but distinctly different celerity behavior. In Chapter 4, a 2D hydro-mechanical model is developed using COMSOL multi-physics modeling software to couple a dual-permeability model with a linear-elastic model. Numerical experiments are conducted for two different rainfall events on a synthetic slope. The influence of preferential flow on slope stability is quantified by comparing the simulated slope failure area for single-permeability model and dual-permeability models. The single-permeability model only simulate regular wetting fronts propagating downward without representing the preferential flow. In contrast, the dual-permeability model can simulate the influence of preferential flow including the enhanced drainage that facilities pressure dissipation under low-intensity rainfall, as well as the fast pressure build-up that may trigger landslides under high-intensity rainfall. The dual-permeability model resulted in a smaller failure area than the corresponding single-permeability model under low-intensity rainfall, while the dual-permeability model resulted in a larger failure area and earlier timing than the corresponding single-permeability model for high-intensity rainfall. In Chapter 5, a parsimonious 1D hydro-mechanical model is developed for field application by coupling a 1D dual-permeability model with an infinite slope stability analysis approach. The numerical model is benchmarked against the HYDRUS-1D for the simulation of non-equilibrium flow. In Chapter 6, the model is applied to simulate the pressure response in a clay-shales slope located in northern Italy. In the study area, preferential flow paths such as tension cracks and macropores are widespread. Intense rain-pulses in the summer can cause nearly-instant pressure responses which may reactivate landslide movement. The water exchange coefficient of the dual-permeability model is calibrated for two single-pulse rainfall-events in the summer, while all other parameters are obtained from field investigations. Results from the dual-permeability model are compared to previously published outcomes using a linear-diffusion equation, where the diffusion coefficient was calibrated for each rainfall event separately. The dual-permeability model explicitly accounts for the influence of both matrix flow and preferential flow on water flow and pressure propagation in variably saturated soils, and is able to simulate the measured pressure response to multi-pulse rainfall-events quite well even in the winter time. Results indicate that the dual-permeability model may be more appropriate for the prediction of landslide-triggering when the pore water pressure response is influenced by preferential flow under high-intensity rainfall.Water Resource

How to Use COMSOL Multiphysics for coupled dual-permeability hydrological and slope stability modeling

Preferential flow paths, such as cracks, macropores, fissures, pipes etc. are common features of highly heterogeneous slopes. During intense rainstorms, preferential flow has a significant influence on subsurface flow and slope stability. Dual-permeability models are widely used to simulate preferential flow, but have not been incorporated into hydro-mechanical models. In this study, the COMSOL Multiphysics software was used to couple a dual-permeability model with a soil mechanics model for landslide stability evaluation on a hillslope scale with examples of up to 100m spatial scale. Detailed information is provided on how to incorporate current hydrological and soil mechanics theories into COMSOL. The model is benchmarked against two existing solutions and is applied to evaluate the effect of preferential flow on slope stability as an example.Water ManagementCivil Engineering and Geoscience

Quantification of the influence of preferential flow on slope stability using a numerical modelling approach

The effect of preferential flow on the stability of landslides is studied through numerical simulation of two types of rainfall events on a hypothetical hillslope. A model is developed that consists of two parts. The first part is a model for combined saturated/unsaturated subsurface flow and is used to compute the spatial and temporal water pressure response to rainfall. Preferential flow is simulated with a dual-permeability continuum model consisting of a matrix domain coupled to a preferential flow domain. The second part is a soil mechanics model and is used to compute the spatial and temporal distribution of the local factor of safety based on the water pressure distribution computed with the subsurface flow model. Two types of rainfall events were considered: long-duration, low-intensity rainfall, and short-duration, high-intensity rainfall. The effect of preferential flow on slope stability is assessed through comparison of the failure area when subsurface flow is simulated with the dual-permeability model as compared to a single-permeability model (no preferential flow). For the low-intensity rainfall case, preferential flow has a positive effect on drainage of the hillslope resulting in a smaller failure area. For the high-intensity rainfall case, preferential flow has a negative effect on the slope stability as the majority of rainfall infiltrates into the preferential flow domain when rainfall intensity exceeds the infiltration capacity of the matrix domain, resulting in larger water pressure and a larger failure area.Water ManagementCivil Engineering and Geoscience

Coupling a 1D Dual-permeability Model with an Infinite Slope Stability Approach to Quantify the Influence of Preferential Flow on Slope Stability

In this study, a 1D hydro-mechanical model was developed by coupling a dual-permeability model with an infinite slope stability approach to investigate the influence of preferential flow on pressure propagation and slope stability. The dual-permeability model used two modified Darcy-Richards equations to simultaneously simulate the matrix flow and preferential flow in a slope. The simulated pressure head was sequentially coupled with the soil mechanics model. The newly-developed numerical model was codified with the Python programming language, and benchmarked against the HYDRUS-1D software. The benchmark example showed that the proposed model is able to simulate the non-equilibrium phenomenon in a heterogeneous soil. We further implemented the model to conduct a synthetic experiment designing a slope with heterogeneous soil overlying an impermeable bedrock as a combined analysis of hydrology and slope stability, the results shows that the occurrence of preferential flow can reducing the time and rainfall amount required for slope failure. The proposed model provides a relatively simple and straightforward way to quantify the effect of preferential flow on the pressure propagation and landslide-triggering in heterogeneous hillslope.Water Resource

Quantification of the influence of preferential flow on slope stability using a numerical modeling approach (discussions)

The effect of preferential flow on the stability of landslides is studied through numerical simulation of two types of rainfall events on a hypothetical hillslope. A model is developed that consists of two parts. The first part is a model for combined saturated/unsaturated subsurface flow and is used to compute the spatial and temporal water pressure response to rainfall. Preferential flow is simulated with a dual-permeability continuum model consisting of a matrix domain coupled to a preferential flow domain. The second part is a~soil mechanics model and is used to compute the spatial and temporal distribution of the local factor of safety based on the water pressure distribution computed with the subsurface flow model. Two types of rainfall events were considered: long duration, low-intensity rainfall, and short duration, high-intensity rainfall. The effect of preferential flow on slope stability is assessed through comparison of the failure area when subsurface flow is simulated with the dual-permeability model as compared to a single-permeability model (no preferential flow). For the low-intensity rainfall case, preferential flow has a positive effect on the slope stability as it drains the water from the matrix domain resulting in a smaller failure area. For the high-intensity rainfall case, preferential flow has a negative effect on the slope stability as the majority of rainfall infiltrates into the preferential flow domain when rainfall intensity exceeds the infiltration capacity of the matrix domain, resulting in larger water pressure and a larger failure area.Water ManagementCivil Engineering and Geoscience

Can flow velocity distribution at a pore-scale be quantified by a celerity-saturation curve?

Water ManagementCivil Engineering and Geoscience

Analysing the influence of preferential flow on pressure transmission and landslide triggering

Water ManagementCivil Engineering and Geoscience

Omega-3 fatty acid eicospentaenoic acid attenuates MPP+-induced neurodegeneration in fully differentiated human SH- SY5Y and primary mesencephalic cells

Eicosapentaenoic acid ( EPA), a neuroactive omega-3 fatty acid, has been demonstrated to exert neuroprotective effects in experimental models of Parkinson's disease ( PD), but the cellular mechanisms of protection are unknown. Here, we studied the effects of EPA in fully differentiated human SH-SY5Y cells and primary mesencephalic neurons treated with MPP+. In both in-vitro models of PD, EPA attenuated an MPP+-induced reduction in cell viability. EPA also prevented the presence of electron-dense cytoplasmic inclusions in SH-SY5Y cells. Then, possible mechanisms of the neuroprotection were studied. In primary neurons, EPA attenuated an MPP+-induced increase in Tyrosine-related kinase B (TrkB) receptors. In SH-SY5Y cells, EPA down-regulated reactive oxygen species and nitric oxide. This antioxidant effect of EPA may have been mediated by its inhibition of neuronal NADPH oxidase and cyclo-oxygenase-2 ( COX-2), as MPP+ increased the expression of these enzymes. Furthermore, EPA prevented an increase in cytosolic phospholipase A2 ( cPLA2), an enzyme linked with COX-2 in the potentially pro-inflammatory arachidonic acid cascade. Lastly, EPA attenuated an increase in the bax:bcl-2 ratio, and cytochrome c release. However, EPA did not prevent mitochondrial enlargement or a decrease in mitochondrial membrane potential. This study demonstrated cellular mechanisms by which EPA provided neuroprotective effects in experimental P

The impact of non-isothermal soil moisture transport on evaporation fluxes in a maize cropland

The process of evaporation interacts with the soil, which has various comprehensive mechanisms. Multiphase flow models solve air, vapour, water, and heat transport equations to simulate non-isothermal soil moisture transport of both liquid water and vapor flow, but are only applied in non-vegetated soils. For (sparsely) vegetated soils often energy balance models are used, however these lack the detailed information on non-isothermal soil moisture transport. In this study we coupled a multiphase flow model with a two-layer energy balance model to study the impact of non-isothermal soil moisture transport on evaporation fluxes (i.e., interception, transpiration, and soil evaporation) for vegetated soils. The proposed model was implemented at an experimental agricultural site in Florida, US, covering an entire maize-growing season (67 days). As the crops grew, transpiration and interception became gradually dominated, while the fraction of soil evaporation dropped from 100% to less than 20%. The mechanisms of soil evaporation vary depending on the soil moisture content. After precipitation the soil moisture content increased, exfiltration of the liquid water flow could transport sufficient water to sustain evaporation from soil, and the soil vapor transport was not significant. However, after a sufficient dry-down period, the soil moisture content significantly reduced, and the soil vapour flow significantly contributed to the upward moisture transport in topmost soil. A sensitivity analysis found that the simulations of moisture content and temperature at the soil surface varied substantially when including the advective (i.e., advection and mechanical dispersion) vapour transport in simulation, including the mechanism of advective vapour transport decreased soil evaporation rate under wet condition, while vice versa under dry condition. The results showed that the formulation of advective soil vapor transport in a soil-vegetation-atmosphere transfer continuum can affect the simulated evaporation fluxes, especially under dry condition.Water Resource