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Brunner, Philip
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Brunner, Philip
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Professeur ordinaire
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philip.brunner@unine.ch
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Voici les éléments 1 - 10 sur 143
- PublicationAccès libreInfiltration and recharge processes in semi-arid regionsLes processus d'infiltration et de recharge jouent un rôle important dans le cycle hydrologique. Une estimation robuste de la recharge est essentielle pour une gestion durable des ressources en eau, en particulier dans les régions arides et semi-arides où l'eau de surface est limitée et les eaux souterraines constituent la principale source d'eau tout au long de l'année. Cependant, l'estimation de la recharge reste un défi, car de nombreux processus importants sont difficiles à mesurer. Par exemple, les processus d'évaporation et de transpiration influencent fortement la dynamique de la recharge, mais sont difficiles à quantifier. De plus, les taux de transpiration et d'évaporation sont également influencés par la profondeur de la nappe phréatique. La présence de végétation influence l'interception des précipitations, affectant ainsi la dynamique de la recharge, et cette influence est difficile à quantifier. L'objectif de cette thèse est d'accroître la robustesse de l'estimation de la recharge, en se concentrant sur les régions semi-arides. La thèse s'appuie sur une combinaison de mesures lysimétriques dans le bassin du Guanzhong et dans le désert de Mu Us avec des modèles numériques. Dans la première contribution, une évaluation systématique de la fiabilité de quatre méthodes couramment utilisées pour estimer l'évaporation du sol nu est réalisée en tenant compte de la profondeur variable de la nappe phréatique. Les résultats montrent que la méthode de la production maximale d'entropie a donné les meilleurs résultats pour toutes les profondeurs de nappe phréatique. La profondeur d'extinction (profondeur maximale d’évapotranspiration) est un indicateur important à considérer pour les méthodes d'estimation de l'évaporation. Ensuite, l'influence de l'arbuste, Salix psammophila, sur le processus d'infiltration est étudiée dans des conditions de nappe phréatique peu profonde et profonde. Salix psammophila est une phréatophyte capable d'absorber de l'eau à la fois de la nappe phrééatique et de la zone vadose. En particulier, la répartition de la densité des racines en réponse à des profondeurs de nappe phréatique peu profondes et profondes a été systématiquement analysée. Nous concentrons notre recherche sur cette espèce spécifique, car dans les projets de reforestation à grande échelle en cours dans le désert de Mu Us, la Chine utilise cette espèce. Les résultats montrent que le reboisement de Salix psammophila peut provoquer une baisse de la nappe phréatique, empêcher la recharge des eaux souterraines et réduire l'infiltration effective. Dans la troisième contribution, la thèse se concentre sur l'investigation de la possibilité d'extraire de manière unique la recharge réelle à partir de modèles de flux souterrain variablement saturé. Étant donné que les modèles de flux souterrain variablement saturé conceptualisent et simulent le mouvement de l'eau à la fois dans les zones non saturées et saturées, il est attendu que la recharge puisse être extraite de manière fiable à partir de ce type de modèles. Les résultats montrent que la recharge réelle ne peut pas être extraite de manière unique des modèles de flux souterrain variablement saturé, contrairement à la recharge potentielle. Enfin, nous avons évalué les performances de différentes méthodes pour estimer la porosité efficace lors de l'estimation de la recharge sous différentes conditions de nappe phréatique. Les résultats indiquent que l'estimation de la recharge peut être améliorée par l'utilisation de porosités efficaces dépendantes de la profondeur, sous réserve de l'acquisition de paramètres fiables. D'un point de vue méthodologique, la combinaison de mesures lysimétriques avec différentes profondeurs de nappe phréatique et de modèles de flux souterrain variablement saturé constitue une approche puissante pour explorer les processus d'infiltration et de recharge dans des conditions naturelles. 摘要 入渗和补给过程在水文循环中发挥着重要作用 。 加强 地下水补给 量的准确估计 对于 水资源的可持续开发利用至关重要 尤其是在干旱和半干旱地区， 地表水资源匮乏，地 下水成为全年重要的水源。然而，由于影响补给量估计的因素难以观测，因此精确计算 地下水的补给量仍面临挑战。例如，蒸散发过程对补给的动态变化有显著影响，但很难 进行定量分析。此外，地下水的埋深也会影响蒸散发速率。植被的存在能够截留降雨， 进一步影响补给的动态变化速率，但这种影响同样难以定量化 。 论文将在半干旱区关中盆地和毛乌素沙地开展一系列的蒸渗仪实验 并 结合数值模 拟的方法，研究入渗和补给的机理， 增强 补给计算的可靠性。 论文的第一个贡献是 ，考虑在影响入渗补给动态方面蒸发的重要性，论文 系 统评估 了四种常 用的裸土蒸发量计算方法在不同的地下水位埋深条件下计算蒸发量的可靠性 。 研究表明最大熵增蒸散法在不同地下水位埋深条件下都能较好地计算蒸发量。 极限蒸发 深度是选择蒸发量计算方法的重要参考指标。 随后 ，研究了毛乌素沙地典型的灌木（沙柳 Salix psammophila）在浅地下水位埋 深和深地下水位埋深条件下对入渗补给过程的影响。沙柳是一种能吸收地下水和包气带 水的深根植物。 需要重点指出的是 ，本文系统地分析了在浅水位和深水位深度的条件下 根系密度的分布状态。之所以本论文重点研究沙柳是因为在中国毛乌素沙地当前的大规 模植树项 目中，沙柳被广泛地种植。 研究表明种植沙柳会引起地下水位下降 ，减少地下 水的补给和降雨有效入渗量。 第三个贡献 论文重点研究了是否可以从变饱和地下水流模型中得到唯一且可靠的 实际地下水补给量。由于变饱和地下水流模型能够同时模拟饱和带和非饱和带水流，因 此人们对从该模型中获取可靠的补给量寄予厚望。研究表明，基于变饱和地下水流模型 无法 获得 唯一可靠的实际补给量，但可以获得唯一的潜在地下水补给量 。 最后 ，论文评价了在不同地下水位埋深条件下，采用不同的给水度定义方法计算地 下水补给量的可靠性，尤其是系统地分析了与地下水位埋深有 关的给水度计算补给量的 可靠性。 研究结果表明如果可以获得可靠的土壤水分特征曲线参数，采用考虑地下水位 埋深的给水度可以提高地下水位补给量计算的精度。 从方法的角度来看，将不同地下水位埋深的蒸渗仪试验与变饱和的地下水流数值模 型的方法 相结合 能够有效地 用于探索自然条件下的入渗和补给过程。 Abstract Infiltration and recharge processes play an important role in the hydrological cycle. Robust estimation of recharge is critical for sustainable water resource management, especially in arid and semi-arid regions where surface water is limited and groundwater constitutes the main source of water throughout the year. However, the estimation of recharge remains a challenge as many of the controlling factors are difficult to measure. For example, evaporation and transpiration processes strongly influence recharge dynamics but are difficult to quantify. Moreover, transpiration and evaporation rates are also influenced by the depth to groundwater. The presence of vegetation influences the interception of rainfall, further affecting recharge dynamics, and this influence is difficult to quantify. The goal of this thesis is to increase the robustness of recharge estimation, with a focus on semi-arid regions. The thesis is based on a combination of lysimeter experiments in Guanzhong Basin and Mu Us Sandy Land with numerical models. In the first contribution, a systematic assessment of the reliability of four commonly used methods for estimating bare soil evaporation is carried out under consideration of variable depth to groundwater. The results show that the maximum entropy production method performed best for all water table depths. The extinction depth is an important indicator for considering methods for estimating evaporation. Subsequently, the influence of shrub (Salix psammophila) on the infiltration process is investigated under both shallow and deep water table conditions. Salix psammophila is a phreatophyte which can absorb water from both groundwater and the vadose zone. In particular, the distribution of root density in response to shallow and deep water table depths was systematically analyzed. We focus our research on this specific species, as in the current, large reforestation projects in Mu Us Sandy Land, China is using this species. The results show that Salix psammophila afforestation can cause a decline of the water table, prevent groundwater recharge, and reduce effective infiltration. In the third contribution, the thesis focuses on investigating whether actual recharge can be uniquely extracted from variably saturated subsurface flow models. As variably saturated subsurface flow models conceptualize and simulate water flow in both the unsaturated and saturated zones, recharge is expected to be reliably extracted from such kinds of models. The results show that actual recharge cannot be uniquely extracted from variably saturated subsurface flow models, as opposed to the potential recharge. Finally, we evaluated the performances of different methods to estimate specific yield for estimating recharge under different water table conditions. In particular, the depth-dependency of specific yields was examined for estimating recharge. The results indicate that the estimation of recharge can be enhanced through the utilization of depth-dependent specific yield, contingent upon the acquisition of reliable parameters. From a methodological point of view, the combination of lysimeter experiments with different water table depths and variably-saturated subsurface flow models constituted a powerful approach for exploring infiltration and recharge processes under natural conditions.
- PublicationAccès libreTowards unprecedented spatiotemporal observations in hydrological systems using Uncrewed Vehicles(2023)
; L'amélioration de la gestion des ressources en eau a été un grand défi et l'utilisation appropriée de l'eau est d'une grande importance pour les écosystèmes et la population humaine dans le monde entier. Le changement climatique affecte le cycle de l'eau et donc l'utilisation de l'eau et les activités humaines dans le monde entier. Il est donc de plus en plus nécessaire de mieux surveiller les ressources en eau et de comprendre les processus hydrogéologiques qui se déroulent dans les systèmes hydrologiques et hydrogéologiques. La technologie de la télédétection a été intensivement utilisée pour surveiller les masses d'eau, mais jusqu'à présent principalement par le biais de satellites et d'avions pilotés. Cependant, des limites subsistent en termes de résolution des données et de manque de données in situ dans les zones isolées et difficilement accessibles. Il est donc nécessaire de disposer de technologies plus avancées permettant d'observer l'eau à des échelles spatiales et temporelles plus fines. Dans ce contexte, les drones, avec leur technologie autonome innovante et leurs résolutions spatio-temporelles élevées, ouvrent une nouvelle ère dans l'étude des systèmes hydrogéologiques. Les véhicules aériens sans pilote (UAV) ont été utilisés dans les études hydrogéologiques en raison de leur souplesse opérationnelle, notamment leur capacité à voler à basse altitude, dans des environnements difficiles et à tout moment, à faible coût. Cette souplesse permet de surmonter les faibles résolutions spatiales et temporelles des données satellitaires et les coûts élevés de l'acquisition de données par des avions pilotés. Outre les drones, les véhicules de surface sans pilote (USV) ont également été utilisés pour l'étude des océans en raison de leur autonomie et de leur navigation à longue distance. Leurs fréquences d'échantillonnage élevées et leur capacité à échantillonner directement la surface de l'océan et pas seulement quelques mètres en dessous, les rendent plus favorables que les plateformes de mesure in situ traditionnelles telles que les bouéesou d'autres bateaux habités. L'objectif de cette thèse de doctorat est d'améliorer la compréhension des processus hydrogéologiques en utilisant cette technologie innovante des véhicules sans pilote. En combinant diverses plateformes et données de télédétection, nous avons produit de nouveaux ensembles de données pour la communauté scientifique avec des résolutions spatio-temporelles sans précédent. Nos études, qui utilisent ces données transportées par des véhicules sans pilote avec des résolutions spatio-temporelles sans précédent, prouvent l'efficacité et le potentiel de la technologie des véhicules sans pilote. Nous menons quatre études différentes liées à différents processus hydrogéologiques dans différents environnements. La première étude est une contribution technique aux techniques de cartographie de la neige à l'aide de la technologie LiDAR embarquée sur drone. La deuxième étude, qui est la toute première étude menée sur un terrain forestier escarpé à l'aide d'un LiDAR embarqué sur un drone, démontre l'effet de la structure de la canopée et du rayonnement solaire sur la formation de motifs de neige dans les pentes forestières escarpées. Nous avons également obtenu des contributions techniques précieuses pour des campagnes similaires à venir. La troisième étude porte sur la dynamique de la température de surface de la mer sur la côte californienne et prouve que Saildrone, un bateau de surface sans équipage, est capable de valider les produits satellitaires grâce à sa fréquence d'échantillonnage d'une minute. Il s'agit de la première étude comparant les produits satellitaires MODIS niveau 2 et MUR (Multi-scale Ultrahigh Resolution) niveau 4 sur la côte californienne et de la première étude évaluant la précision des niveaux de qualité MODIS niveau 2 sur la côte californienne. La dernière étude vise à cartographier la matière organique de la couche arable à haute résolution en exploitant les propriétés spectrales du sol ainsi que les analyses traditionnelles en laboratoire. ABSTRACT The improvement of water resources management has been a big challenge and the appropriate use of water is of high importance for the ecosystems and the human population globally. Climate change affects the water cycle and therefore water use and human activities around the world. There is therefore an increased need for better monitoring of the water resources and the understanding of the hydrogeological processes that take place in hydrological and hydrogeological systems. Remote sensing technology has been intensively used to monitor water bodies, but so far mainly via satellites and crewed aircraft. However, there are still limitations in terms of data resolution and lack of in situ data in isolated and difficultly accessible areas. Therefore, there is a need for more advanced technologies that can observe the water at finer spatial and temporal scales. In this context, uncrewed vehicles with their innovative autonomous technology and their high spatiotemporal resolutions open a new era in the study of hydrogeological systems. Uncrewed aerial vehicles (UAVs) have been used in hydrogeological studies due to their operational flexibilities such as their ability to fly at low altitudes, in challenging environments, and whenever the user needs them at low costs. These flexibilities overcome the low spatial and temporal resolutions of the satellite data and the high costs of crewed aircraft data acquisitions. Besides the UAVs, uncrewed surface vehicles (USVs) have also been used in ocean studies due to their autonomous and long-range navigation. Their high sampling frequencies and their ability to directly sample the ocean surface and not just a few meters underneath, make them more favorable than traditional in situ measurement platforms such as buoys or other crewed boats. The aim of this Ph.D. thesis is to improve the understanding of hydrogeological processes using this innovative technology of uncrewed vehicles. By combining various remote sensing platforms and data, we produced new datasets for the scientific community with unprecedented spatiotemporal resolutions. Our studies, using these uncrewed vehicle-borne data with their unprecedented spatiotemporal resolutions, prove the efficiency and potential of the uncrewed vehicle technology. We pursue four different studies related to different hydrogeological processes in different environments. The first study is a technical contribution to snow mapping techniques using UAVborne LiDAR technology. The second study, which is the first-ever study conducted in steep forested terrain using UAV-borne LiDAR demonstrates the effect of canopy structure and solar radiation in the formation of snow patterns within the steep forested slopes. We also extract valuable technical contributions for similar future campaigns. The third study focuses on sea surface temperature dynamics on the California Coast and proves that Saildrone, an uncrewed surface boat, is capable of validating satellite products with its one-minute sampling frequency. It is the first study to compare MODIS level-2 with Multi-scale Ultra-high Resolution (MUR) level-4 satellite products over the California Coast and the first one to assess the accuracy of MODIS level-2 quality levels over the California Coast. The last study aims at mapping topsoil organic matter at high resolution by exploiting the soil spectral properties along with traditional laboratory analysis. - PublicationAccès libreNoble gases as tracers of surface water – groundwater interactions: insights from novel field and modelling approachesUnderstanding the interactions between surface water (SW) and groundwater (GW) in alluvial aquifer systems is of critical importance for the sustainable management of water resources. Advances in realtime and continuous measurement of a range of hydrological tracers provide new opportunities for the characterization of SW-GW dynamics at unprecedented spatiotemporal resolutions. Amongst several promising tracer methods, noble gases are particularly well-adapted to the study of SW-GW interactions, and provide an integrated signal on the flow paths and travel times of water. Capitalizing on the insights offered by novel measurement technologies requires tracer interpretation methods that appropriately capture tracer transport processes in dynamic environmental conditions. However, recourse to highly-simplified tracer interpretation methods, conceptually detached from the complexity of natural systems, is still widespread. In such cases, the potentially rich information content of tracer measurements may be underutilized. This thesis aims at investigating how established and emerging noble gas tracer methods can be optimally used - and when they should be avoided - for the study of SW-GW interactions in alluvial aquifer systems. To this end, a range of novel laboratory, field, and modelling approaches are employed to systematically assess the applicability, limitations, and potential of some gas tracer methods toward informing SW-GW exchange processes. The first gas tracer method examined is the 222Rn apparent age model, which is widely used to estimate the ages of very young GW (days to weeks). High-resolution measurements of the spatial distribution of 222Rn emanation rates in an alluvial aquifer reveal significant spatial heterogeneity in 222Rn production. The explicit simulation of 222Rn in synthetic mass-transport models shows that this level of heterogeneity, combined with mixing of GW, can result in strongly biased estimates of GW age, effectively limiting the applicability of the 222Rn apparent age method to a limited range of field conditions. Although temporal changes in 222Rn concentrations may reveal insights into GW age dynamics, the information content of 222Rn measurements may be best extracted through the integration of 222Rn observations in the calibration process of physics-based flow and transport models. Indeed, the second part of this thesis is devoted to exploring how the explicit simulation of tracer concentrations and the assimilation of untransformed tracer data in highly parameterized, physicsbased models may inform model parameters and ultimately predictions of management interest. Within this framework, the joint assimilation of hydraulic and noble gas data (222Rn and helium), acquired over the course of a novel tracer injection experiment, is shown to strongly inform model parameters and reduce predictive uncertainty of several important water management quantities, such as GW age, SW-GW mixing ratios, and SW infiltration fluxes, far beyond what is achieved with “traditional” hydraulic data alone. These results build upon mounting evidence as to the benefits of explicitly simulating and assimilating diverse observation types with physically-based flow and transport models, avoiding the layer of conceptual simplification and potential bias accrued with simplified tracer interpretation models. Finally, the successful combination of novel gas injection methods, developed over the course of this project, and the assimilation of high-resolution gas tracer measurements in an explicit tracer simulation framework strongly support further developments of (noble) gas tracer methods and tracer-numerical model synergies.
- PublicationAccès libreA systematic methodology to calibrate wellbore failure models, estimate the in-situ stress tensor and evaluate wellbore cross-sectional geometry(2022-1-1)
; ; ; Alcolea, AndresDeep geothermal boreholes, often drilled to the crystalline basement, suffer from borehole breakouts that compromise borehole stability and/or lead to low drilling performance. These issues increase the cost of deep geothermal projects and lead to irregular cross-sectional geometries that may entangle well completion (e.g., packer isolation for zonal stimulation, cementing, etc.). Thus, the proper knowledge of rock strength, state of stress and their interactions at the closest vicinity of the borehole is key to the success of deep geothermal drilling. Typically, the magnitudes of the vertical and minimum horizontal principal stresses, 𝑆𝑣 and 𝑆ℎ𝑚𝑖𝑛, respectively, can be estimated while 𝑆𝐻𝑚𝑎𝑥 is difficult to constrain. This paper presents a systematic methodology to jointly evaluate the heterogeneous distributions of the stress tensor principal components and orientations, and the rock strength properties (e.g. cohesion, friction). Model parameters are estimated from measurements available during or shortly after drilling, i.e., breakout width, breakout extent/depth of penetration, breakout orientation and drilling induced tensile fractures. Additionally, measurements of estimated parameters or transformations of them can be considered in the calibration in a generic manner (e.g., 𝑆ℎ𝑚𝑖𝑛 interpreted from XLOT). For illustration purposes, the methodology is applied to the extensive borehole data set along the crystalline section of the borehole BS-1, in Basel (Switzerland). The methodology allows us (1) to derive plausible sets of stress and strength parameters reproducing the complex distribution of breakouts along BS-1, and (2) to unveil the paradox of having no borehole breakouts at sections with high density of natural fractures. - PublicationAccès libreUav-Based LIDAR High-Resolution Snow Depth Mapping in the Swiss Alps: Comparing Flat and Steep ForestsSnow depth mapping in Alpine forests is of high importance for hydrogeology, ecology, tourism, and natural hazards prevention. Different remote sensing approaches have been employed for the precise mapping of snow depth within forests. However, optical sensors cannot provide below-canopy information. While Airborne Laser Scanning (ALS) systems have been used successfully in this context and allow obtaining data below canopies, the costs of acquisitions are very high, not allowing frequent data acquisitions. UAV-based Lidar technology potentially can provide the critical below-canopy information at lower cost and allows for frequent acquisitions. First attempts to employ a UAV-based Lidar system in forests have proven promising, but they are limited to flat forests and to grid-level snow depth calculations. In this study, we present UAV-based Lidar data of both flat and steep forests. Different Lidar processing workflows are analyzed and compared, and snow depth algorithms are used both at the point and the grid level. Whereas the UAV-Lidar system proved capable of mapping snow in both environments, the steep forests' data processing comes with greater challenges, especially for the 3D registration, ground classification, and point-to-point snow depth calculations.
- PublicationAccès libreTransit-time and temperature control the spatial patterns of aerobic respiration and denitrification in the riparian zone(2021-11)
; - PublicationAccès libreSources of Surface Water in Space and Time: Identification of Delivery Processes and Geographical Sources With Hydraulic Mixing-Cell Modeling(2021-10)
; - PublicationAccès libreSimulation of nitrogen dynamics in lowland polders using a new coupled modelling approach: Insights into management(2021-8)
; Gao, JunfengA new modelling framework, the Polder Hydrology and Nitrogen modelling System (PHNS), was developed to simulate the nitrogen dynamics and processes in polder systems. PHNS is a mass-balance model that simulates water and nitrogen dynamics in soil and surface water systems through integrating the WALRUS-paddy, MUSLE, and INCA models. The model explicitly considers the interactions among surface water, groundwater, and vadose water, as well as irrigation, pumping, and fertilizer application, which are the key processes controlling the nitrogen cycle in polders. The sensitivity analysis, calibration, and validation of the developed model were conducted in a Chinese agricultural polder by using three years of measured hydro-meteorological data. The calibrated and validated results proved that the model has a good performance with an R2 of 0.748 and a Nash- Sutcliffe (NS) efficiency coefficient of 0.619 for total nitrogen (TN) concentration during the validation period. The nitrogen budget results (net export of 40.4 kg/ha/yr) revealed that the polder is a nitrogen source for downstream freshwater systems. Reducing the amount of fertilizers, retaining crop residues, and restoring aquatic plants in surface water are effective countermeasures for reducing nitrogen export from polders. This study provides an efficient modelling tool and useful insights into polder management. - PublicationAccès libreCross-sphere modelling to evaluate impacts of climate and land management changes on groundwater resources(2021-8)
; ; ; - PublicationAccès libreSalix psammophila afforestations can cause a decline of the water table, prevent groundwater recharge and reduce effective infiltration(2021-8)
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