Fostering assumption-based stress-test thinking in managing groundwater systems: learning to avoid failures due to basic dynamics     

Joseph H. A. Guillaume  Sondoss El Sawah 《Hydrogeology Journal》2014,22(7):1507-1523

Sustainable groundwater resource management can only be achieved if planning processes address the basic dynamics of the groundwater system. Conceptual and distributed groundwater models do not necessarily translate into an understanding of how a plan might operate in reality. Prompted by Australian experiences, ‘iterative closed-question modelling’ has been used to develop a process of iterative dialogue about management options, objectives and knowledge. Simple hypothetical models of basic system dynamics that satisfy agreed assumptions are used to stress-test the ability of a proposed management plan to achieve desired future conditions. Participants learn from models in which a plan succeeds and fails, updating their assumptions, expectations or plan. Their new understanding is tested against further hypothetical models. The models act as intellectual devices that confront users with new scenarios to discuss. This theoretical approach is illustrated using simple one and two-cell groundwater models that convey basic notions of capture and spatial impacts of pumping. Simple extensions can address uncertain climate, managed-aquifer recharge and alternate water sources. Having learnt to address the dynamics captured by these models, participants may be better placed to address local conditions and develop more effective arrangements to achieve management outcomes.  相似文献   

Gamma-ray binaries and related systems     

Guillaume?DubusEmail author 《Astronomy and Astrophysics Review》2013,21(1):64

After initial claims and a long hiatus, it is now established that several binary stars emit high- (0.1–100 GeV) and very high-energy (>100 GeV) gamma rays. A new class has emerged called “gamma-ray binaries”, since most of their radiated power is emitted beyond 1 MeV. Accreting X-ray binaries, novae and a colliding wind binary (η Car) have also been detected—“related systems” that confirm the ubiquity of particle acceleration in astrophysical sources. Do these systems have anything in common? What drives their high-energy emission? How do the processes involved compare to those in other sources of gamma rays: pulsars, active galactic nuclei, supernova remnants? I review the wealth of observational and theoretical work that have followed these detections, with an emphasis on gamma-ray binaries. I present the current evidence that gamma-ray binaries are driven by rotation-powered pulsars. Binaries are laboratories giving access to different vantage points or physical conditions on a regular timescale as the components revolve on their orbit. I explain the basic ingredients that models of gamma-ray binaries use, the challenges that they currently face, and how they can bring insights into the physics of pulsars. I discuss how gamma-ray emission from microquasars provides a window into the connection between accretion–ejection and acceleration, while η Car and novae raise new questions on the physics of these objects—or on the theory of diffusive shock acceleration. Indeed, explaining the gamma-ray emission from binaries strains our theories of high-energy astrophysical processes, by testing them on scales and in environments that were generally not foreseen, and this is how these detections are most valuable.  相似文献   

The Corossol structure: A possible impact crater on the seafloor of the northwestern Gulf of St. Lawrence,Eastern Canada     

Patrick Lajeunesse  Guillaume St‐Onge  Jacques Locat  Mathieu J. Duchesne  Michael D. Higgins  Richard Sanfaçon  Joseph Ortiz 《Meteoritics & planetary science》2013,48(12):2542-2558

We report on a 4.1 (±0.2) km diameter and 185 m deep circular submarine structure exposed on the seabed in >40 m water depths in the northwestern Gulf of St. Lawrence (Eastern Canada) from the analysis of high‐resolution multibeam bathymetric and seismic data. The presence of a circular form characterized by a central uplift and concentric rings resembles the morphology and geometry of complex meteorite impact structures. Also, other origins, such as kimberlites, intrusions, karsts, or diapirs, can be eliminated on geological criteria. A single 4 cm long breccia fragment recovered from the central uplift has numerous glassy droplets of fluorapatite composition, assumed to be impact melts, and a single quartz grain with planar intersection features thought to be shock‐induced planar deformation features (PDFs). The absolute age of this possible impact structure is unknown, but its geological setting indicates that it was formed long after the Mid‐Ordovician and before regional pre‐Quaternary sea‐level lowstands. Present results outline the need for further examination to confirm an impact origin and to precisely date the formation of the structure.  相似文献   

Simulation of breaking waves using the high-order spectral method with laboratory experiments: wave-breaking energy dissipation     

Betsy R. Seiffert  Guillaume Ducrozet 《Ocean Dynamics》2018,68(1):65-89

We examine the implementation of a wave-breaking mechanism into a nonlinear potential flow solver. The success of the mechanism will be studied by implementing it into the numerical model HOS-NWT, which is a computationally efficient, open source code that solves for the free surface in a numerical wave tank using the high-order spectral (HOS) method. Once the breaking mechanism is validated, it can be implemented into other nonlinear potential flow models. To solve for wave-breaking, first a wave-breaking onset parameter is identified, and then a method for computing wave-breaking associated energy loss is determined. Wave-breaking onset is calculated using a breaking criteria introduced by Barthelemy et al. (J Fluid Mech https://arxiv.org/pdf/1508.06002.pdf, submitted) and validated with the experiments of Saket et al. (J Fluid Mech 811:642–658, 2017). Wave-breaking energy dissipation is calculated by adding a viscous diffusion term computed using an eddy viscosity parameter introduced by Tian et al. (Phys Fluids 20(6): 066,604, 2008, Phys Fluids 24(3), 2012), which is estimated based on the pre-breaking wave geometry. A set of two-dimensional experiments is conducted to validate the implemented wave breaking mechanism at a large scale. Breaking waves are generated by using traditional methods of evolution of focused waves and modulational instability, as well as irregular breaking waves with a range of primary frequencies, providing a wide range of breaking conditions to validate the solver. Furthermore, adjustments are made to the method of application and coefficient of the viscous diffusion term with negligible difference, supporting the robustness of the eddy viscosity parameter. The model is able to accurately predict surface elevation and corresponding frequency/amplitude spectrum, as well as energy dissipation when compared with the experimental measurements. This suggests the model is capable of calculating wave-breaking onset and energy dissipation successfully for a wide range of breaking conditions. The model is also able to successfully calculate the transfer of energy between frequencies due to wave focusing and wave breaking. This study is limited to unidirectional waves but provides a valuable basis for future application of the wave-breaking model to a multidirectional wave field. By including parameters for removing energy due to wave-breaking into a nonlinear potential flow solver, the risk of developing numerical instabilities due to an overturning wave is decreased, thereby increasing the application range of the model, including calculating more extreme sea states. A computationally efficient and accurate model for the generation of a nonlinear random wave field is useful for predicting the dynamic response of offshore vessels and marine renewable energy devices, predicting loads on marine structures, and in the study of open ocean wave generation and propagation in a realistic environment.  相似文献   

Western boundary upwelling dynamics off Oman     

Clément Vic  Xavier Capet  Guillaume Roullet  Xavier Carton 《Ocean Dynamics》2017,67(5):585-595

Despite its climatic and ecosystemic significance, the coastal upwelling that takes place off Oman is not well understood. A primitive-equation, regional model forced by climatological wind stress is used to investigate its dynamics and to compare it with the better-known Eastern Boundary Upwellings (EBUs). The solution compares favorably with existing observations, simulating well the seasonal cycles of thermal structure, surface circulation (mean and turbulent), and sea-surface temperature (SST). There is a 1.5-month lag between the maximum of the upwelling-favorable wind-stress-curl forcing and the oceanic response (minima in sea-surface height and SST), which we attribute to onshore-propagating Rossby waves. A southwestward-flowing undercurrent (opposite to the direction of the near-surface flow) is also simulated with a core depth of 1000 m, much deeper than found in EBUs (150–200 m). An EKE budget reveals that, in contrast to EBUs, the upwelling jet is more prone to barotropic than baroclinic instability and the contribution of locally-generated instabilities to EKE is higher by an order of magnitude. Advection and redistribution of EKE by standing mesoscale features also play a significant role in EKE budget.  相似文献   

Conceptualization and Calibration of Anisotropic Alluvial Systems: Pitfalls and Biases     

Guillaume Gianni  John Doherty  Philip Brunner 《Ground water》2019,57(3):409-419

Physical properties of alluvial environments typically feature a high degree of anisotropy and are characterized by dynamic interactions between the surface and the subsurface. Hydrogeological models are often calibrated under the assumptions of isotropic hydraulic conductivity fields and steady-state conditions. We aim at understanding how these simplifications affect predictions of the water table using physically based models and advanced calibration and uncertainty analysis approaches based on singular value decomposition and Bayesian analysis. Specifically, we present an analysis of the information content provided by steady-state hydraulic data compared to transient data with respect to the estimation of aquifer and riverbed hydraulic properties. We show that assuming isotropy or fixed anisotropy may generate biases both in the estimation of aquifer and riverbed parameters as well as in the predictive uncertainty of the water table. We further demonstrate that the information content provided by steady-state hydraulic heads is insufficient to jointly estimate the aquifer anisotropy together with the aquifer and riverbed hydraulic conductivities and that transient data can help to reduce the predictive uncertainty to a greater extent. The outcomes of the synthetic analysis are applied to the calibration of a dynamic and anisotropic alluvial aquifer in Switzerland (The Rhône River). The results of the synthetic and real world modeling and calibration exercises documented herein provide insight on future data acquisition as well as modeling and calibration strategies for these environments. They also provide an incentive for evaluation and estimation of commonly made simplifying assumptions in order to prevent underestimation of the predictive uncertainty.  相似文献   

Beach recovery from extreme storm activity during the 2013–14 winter along the Atlantic coast of Europe     

Guillaume Dodet  Bruno Castelle  Gerd Masselink  Timothy Scott  Mark Davidson  France Floc'h  Derek Jackson  Serge Suanez 《地球表面变化过程与地形》2019,44(1):393-401

The storm sequence of the 2013–14 winter left many beaches along the Atlantic coast of Europe in their most eroded state for decades. Understanding how beaches recover from such extreme events is essential for coastal managers, especially in light of potential regional increases in storminess due to climate change. Here we analyse a unique dataset of decadal beach morphological changes along the west coast of Europe to investigate the post-2013–14 winter recovery. We show that the recovery signature is site specific and multi-annual, with one studied beach fully recovered after 2 years, and the others only partially recovered after 4 years. During the recovery phase, winter waves primarily control the timescales of beach recovery, as energetic winter conditions stall the recovery process whereas moderate winter conditions accelerate it. This inter-annual variability is well correlated with climate indices. On exposed beaches, an equilibrium model showed significant skill in reproducing the post-storm recovery and thus can be used to investigate the recovery process in more detail. © 2018 John Wiley & Sons, Ltd.  相似文献   

Quality Assessment of the French OpenStreetMap Dataset   总被引：9，自引：1，他引：8  

Jean‐François Girres  Guillaume Touya 《Transactions in GIS》2010,14(4):435-459

The concept of Volunteered Geographic Information (VGI) has recently emerged from the new Web 2.0 technologies. The OpenStreetMap project is currently the most significant example of a system based on VGI. It aims at producing free vector geographic databases using contributions from Internet users. Spatial data quality becomes a key consideration in this context of freely downloadable geographic databases. This article studies the quality of French OpenStreetMap data. It extends the work of Haklay to France, provides a larger set of spatial data quality element assessments (i.e. geometric, attribute, semantic and temporal accuracy, logical consistency, completeness, lineage, and usage), and uses different methods of quality control. The outcome of the study raises questions such as the heterogeneity of processes, scales of production, and the compliance to standardized and accepted specifications. In order to improve data quality, a balance has to be struck between the contributors' freedom and their respect of specifications. The development of appropriate solutions to provide this balance is an important research issue in the domain of user‐generated content.  相似文献