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Brunner, Philip

Nom
Brunner, Philip
Affiliation principale
Fonction
Professeur ordinaire
Email
philip.brunner@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/165
_
0000-0001-6304-6274

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  • Publication
    Accès libre
    Assessing bare-soil evaporation from different water-table depths using lysimeters and a numerical model in the Ordos Basin, China
    (2019-7)
    Ma, Zhitong
    ;
    Wang, Wenke
    ;
    Zhang, Zaiyong
    ;
    Brunner, Philip 
    ;
    Wang, Zhoufeng
    ;
    Chen, Li
    ;
    Zhao, Ming
    ;
    Gong, Chengcheng
    In semiarid and arid regions, the evaporation from bare soil is highly sensitive to changes in the depth to the water table. This study quantifies the relation between water-table depth and the groundwater contribution to evaporation in the Ordos Basin in China. In-situ field experiments were combined with numerical simulations of heat, vapor and liquid water flow. Based on lysimeter experiments and a calibrated numerical model, a relation between depth to groundwater and evaporation rate was established for the lysimeter site. In addition, a sensitivity analysis considering the hydraulic conductivity and the inverse of the air-entry pressure (vanGenuchten α) was established. For the field site, the results showed that for the water-table depths less than 52 cm below the ground, evaporation is independent of the water-table depth. For water-table depths exceeding 52 cm, an exponential relation between depth to groundwater and evaporation is observed. No phreatic evaporation occurs for water tables deeper than 105 cm, which is nearly two times the capillary fringe height. The sensitivity analysis showed that the extinction depth decreased with decreasing hydraulic conductivity and increased with α. The field-specific results and the sensitivity analysis provide valuable information to understand the dynamic processes of soil evaporation in the Ordos Basin. From a methodological point of view, the proposed modelling approach and the integration of lysimeter data proved to be a highly efficient combination to study evaporation dynamics in semi-arid and arid environments.
  • Publication
    Accès libre
    Physically based hydrogeological and slope stability modeling of the Turaida castle mound
    (2018-7)
    Kukemilks, Karlis
    ;
    Wagner, Jean-Frank
    ;
    Saks, Tomas
    ;
    Brunner, Philip 
    This study explores the potential of integrating state-ofthe- art physically based hydrogeological modeling into slope stability simulations to identify the hydrogeological triggers of landslides. Hydrogeological models considering detailed morphological, lithological, and climatic factors were elaborated. Groundwater modeling reveals locations with elevated pore water pressures in the subsurface and allows the quantification of temporal dynamics of the pore water pressures. Results of the hydrogeological modeling were subsequently applied as boundary conditions for the slope stability simulations. The numerical models illustrate that the hydrogeological impacts affecting hillslope stability are strongly controlled by local groundwater flow conditions and their conceptualization approach in the hydrogeological model. Groundwater flow itself is heavily influenced by the inherent geological conditions and the dynamics of climatic forcing. Therefore, both detailed investigation of the landslide’s hydrogeology and appropriate conceptualization and scaling of hydrogeological settings in a numerical model are essential to avoid an underestimation of the landslide risk. The study demonstrates the large potential in combining state-of-the-art computational hydrology with slope stability modeling in realworld cases.
  • Publication
    Accès libre
    Conceptualization of preferential flow for hillslope stability assessment
    (2017-9)
    Kukemilks, Karlis
    ;
    Wagner, Jean-Frank
    ;
    Saks, Tomas
    ;
    Brunner, Philip 
    This study uses two approaches to conceptualize preferential flow with the goal to investigate their influence on hillslope stability. Synthetic three-dimensional hydrogeological models using dual-permeability and discrete-fracture conceptualization were subsequently integrated into slope stability simulations. The slope stability simulations reveal significant differences in slope stability depending on the preferential flow conceptualization applied, despite similar small-scale hydrogeological responses of the system. This can be explained by a local-scale increase of pore-water pressures observed in the scenario with discrete fractures. The study illustrates the critical importance of correctly conceptualizing preferential flow for slope stability simulations. It further demonstrates that the combination of the latest generation of physically based hydrogeological models with slope stability simulations allows for improvement to current modeling approaches through more complex consideration of preferential flow paths.
  • Publication
    Accès libre
    Numerical simulations and uncertainty analysis for assessing spatial and temporal dynamics in alluvial river-aquifer systems: an application in the context of the 3rd RhĂ´ne River Correction
    (2017)
    Gianni, Guillaume
    ;
    Brunner, Philip 
    ;
    Perrochet, Pierre 
    La caractérisation de l’interaction entre les rivières et les eaux souterraines pour des aquifères alluviaux est essentielle afin d’anticiper l’impact des stratégies de gestion de rivière, comme le sont les restaurations de rivières, sur l’ensemble de la ressource en eau et sur sa dynamique. De ce fait, le développement de méthodes et d’approches de calibration permettant une meilleure caractérisation et estimation des paramètres hydrauliques des aquifères et des lits de rivière est nécessaire. De plus, l’analyse d’hypothèses communes, telles que la constance des propriétés hydrauliques des lits de rivière, l’isotropie de la conductivité hydraulique de l’aquifère ou encore la calibration en régime permanent, est indispensable afin d’identifier des biais potentiels dans les prévisions et leurs incertitudes.
    Le chapitre 1 introduit les concepts pertinents, les méthodes, le cadre de recherche, c.-à-d. la 3e Correction du Rhône, ainsi que le but de la thèse doctorale.
    Le chapitre 2 présente une méthode qui permet d’évaluer le caractère transitoire des propriétés hydrauliques de lits de rivière. La méthode est basée sur l’inversion d’une convolution numérique entre les variations de niveau de la rivière et la réponse unitaire, en terme de variation de la surface piézométrique, de l’aquifère. L’estimation du caractère transitoire des propriétés hydrauliques du lit de la rivière est obtenue par des calibrations utilisant des séries temporelles successives de charges hydrauliques. Une analyse synthétique a démontré la fiabilité de la méthode et son application à des données réelles de terrain a permis d’indiquer l’influence d’événements climatiques sur le caractère transitoire des propriétés hydrauliques.
    Le chapitre 3 analyse les conséquences sur l’estimation de l’incertitude de la prévision de l’hypothèse communément faite sur l’isotropie de la conductivité hydraulique de l’aquifère. Il est démontré que les présupposés sur l’isotropie de l’aquifère peuvent causer une sous-estimation de l’incertitude des prévisions sur l’élévation de la surface piézométrique. De plus, il est démontré que la calibration transitoire, en comparaison à celle en régime permanent, permet une meilleure estimation des paramètres hydrauliques de l’aquifère et du lit de la rivière et ainsi de réduire l’incertitude de la prévision.
    Le chapitre 4 présente les prévisions sur l’élévation de la surface piézométrique et leurs incertitudes dans la région de Sion (Suisse) dans le cadre des modifications projetées par la 3e Correction du Rhône. Ce faisant, l’incertitude de la prévision liée à la calibration du modèle numérique hydrogéologique est complétée par la prise en compte, via la modélisation de scénarios, de l’incertitude sur les futures propriétés hydrauliques et géomorphologiques du lit du Rhône. Les résultats montrent que bien que le processus de calibration réduit de manière importante l’incertitude de la prévision, l’incertitude sur l’élévation future de la surface piézométrique, liée au potentielles variations des propriétés hydrauliques du lit du Rhône reste importante.
    Le chapitre 5 résume les résultats des études présentées, fournis des recommandations quant aux approches de modélisations hydrogéologiques d’une manière générale et dans le cadre de la 3e Correction du Rhône., Characterizing river-groundwater interactions in alluvial aquifers is essential when forecasting the impact of river management strategies, such as river restorations, on the overall water resources distribution and dynamics. Therefore, the development of methods and calibration approaches that allow for better identification of the spatial and temporal characteristics of the hydraulic properties of the aquifer and the riverbed are required. Moreover, the analysis of commonly made assumptions, such as constant hydraulic properties of the streambed, isotropy of the aquifer hydraulic conductivity and steady-state calibration, is important in order to identify potential biases in predictions and related uncertainties.
    Chapter 1 introduces the relevant concepts and methods as well as the framework, i.e. the 3rd RhĂ´ne River Correction, and the purpose of the Ph.D. thesis.
    Chapter 2 presents a method that assesses the temporal variations of the hydraulic properties of the riverbed. The method is based on the inversion of a numerical convolution between an aquifer unit step response and stream stage variations. Calibrations against successive time series of observed water table variations allow to estimate the transience in the riverbed properties. A synthetic analysis demonstrated the robustness of the method and its application to field data pointed out the influence of climatic events on the transience in riverbed hydraulic properties.
    Chapter 3 aims at understanding how simplifications in modeling practice regarding horizontal isotropy of the aquifer hydraulic conductivity affect the estimated uncertainty of predictions. It is demonstrated that assuming isotropy or fixed anisotropy may cause the predictive uncertainty of the water table elevation to be underestimated. Then, by taking into account the uncertainty in aquifer anisotropy, it is shown that calibration against transient data allows to achieve a better estimation of the aquifer and riverbed hydraulic parameters and to reduce the predictive uncertainty of water table elevations.
    Chapter 4 presents the model forecasting and related uncertainty of the water table elevation in the area of Sion (Switzerland) in the framework of the modifications projected by the 3rd RhĂ´ne River Correction. Furthermore, the predictive uncertainty related to model calibration is complemented by scenario modeling taking into account the uncertainties in the future state of the RhĂ´ne riverbed hydraulic properties and geomorphologies. The results show that although the calibration process can significantly reduce the predictive uncertainty, the uncertainty in the future elevation of the water table, related to potential variations in the hydraulic properties of the RhĂ´ne riverbed, remains important.
    Chapter 5 summarizes the results of the studies and provides recommendations and perspectives regarding hydrogeological modeling approaches in general and in the framework of 3rd RhĂ´ne River Correction.
  • Publication
    Accès libre
    Heterogeneous or homogeneous? Implications of simplifying heterogeneous streambeds in models of losing streams
    (2012)
    Irvine, Dylan J.
    ;
    Brunner, Philip 
    ;
    Hendricks Franssen, Harrie-Jan
    ;
    Simmons, Craig T.
    A common approach in modeling surface water–groundwater interaction is to represent the streambed as a homogeneous geological structure with hydraulic properties obtained by means of model calibration. In reality, streambeds are highly heterogeneous, and there are currently no methodical investigations to justify the simplification of this geologic complexity. Using a physically based numerical model, synthetic surface water–groundwater infiltration flux data were generated using heterogeneous streambeds for losing connected, losing transitional and losing disconnected streams. Homogeneous streambed hydraulic conductivities were calibrated to reproduce these fluxes. The homogeneous equivalents were used for predicting infiltration fluxes between streams and the aquifer under different hydrological conditions (i.e. for different states of connection). Homogeneous equivalents are shown to only accurately reproduce infiltration fluxes if both the calibration and prediction are made for a connected flow regime, or if both the calibration and prediction are made for a disconnected flow regime. The greatest errors in flux (±34%) using homogeneous equivalents occurred when there was a mismatch between the flow regime of the observation data and the prediction. These errors are comparatively small when compared with field measurement errors for hydraulic conductivity, however over long river reaches these errors can amount to significant volumes of water.