1,721,056 research outputs found
Non-ergodic solute transport in self-similar porous formations: the effect of conditioning
No full textWe analyze the influence of conditioning to hydraulic transmissivity measurements on transport of a conservative tracer in a two-dimensional evolving-scale formation with a large-scale cutoff of the hydraulic transmissivity. First-order analytical solutions of ensemble and effective plume moments, conditional to a single measurement of hydraulic transmissivity, are provided for an instantaneous release of solute within a linear source normal to the mean flow direction. The proposed solutions show that both ensemble and effective moments are significantly affected by the additional information brought into flow and transport models through conditioning to available data. We conclude that the effect of conditioning to available measurements is more pronounced on the ensemble moments than on the effective moments, and uncertainty is not reduced in the same proportion for longitudinal and transverse effective second moments, since the former shows the largest reduction of uncertainty for a given measurement location. This result confirms the experimental findings showing larger uncertainty in the estimation of the transverse moments. Furthermore, for all moments the impact of the measurement reduces with the distance of the measurement point from the mean plume trajectory. (C) 2003 Elsevier Science Ltd. All rights reserved
Non-ergodic transport of kinetically sorbing solutes
No full textThe fate of contaminants in groundwater is controlled by many factors; the most relevant are the formation heterogeneities, the geochemical properties of the aquifer and the source size which is a limiting factor for the spreading of the contaminant. When the source size is much lager than the characteristic scale of the formation heterogeneities, the transport develops under ergodic conditions and the spatial moments of the plume are not influenced by the source size. In this case, the plume samples all the relevant scales of heterogeneity and the spreading of the solute reaches its maximum. To date, a number of solutions are available for transport under ergodic conditions and only few studies address the non-ergodic case, which develops when the source size is of the same order of magnitude of the formation integral scale, In this paper, we study how the source size affects the transport of linear kinetically sorbing solutes, characterized by constant reaction parameters. First, the general expressions for the effective plume moments in natural formations are obtained by using the Lagrangian approach. Then, closed form solutions are provided for instantaneous injection over a plane normal to the mean flow direction and in the limiting case of large travel times, in addition, we analyze the plume moments at small and moderate times in an isotropic two-dimensional formation characterized by the Gaussian log-conductivity covariance function. We found that the source size is the key factor controlling the relative impact on transport of the formation heterogeneities and the geochemical properties of the aquifer. In addition, we found that the relative importance of the contribution to dispersion stemming from the formation heterogeneities increases with the source size. Conversely, when the source size is comparable with the Darcy's scale, the formation heterogeneities do not contribute to solute spreading, which is controlled by the reaction only. The results show also that the ergodic conditions for the longitudinal second order moment are obtained with a progressively smaller source size as the reaction rates increases. Hence, the presence of reaction facilitates the occurrence of ergodic transport, which is obtained for plumes significantly smaller than for nonreactive solutes transport. (C) 1999 Elsevier Science B.V. All rights reserved
DIRECT DYNAMIC FORCE MEASUREMENY ON SLABS IN SPILLWAY STILLING BASINS
No full textJOURNAL OF HYDRAULICH ENGINEERING A.S.C.E
Diffusione e dispersione - L'approccio numerico
No full textAppendice alla relazione generale "Diffusione e dispersione
Flusso verso un pozzo in acquiferi naturali: simulazioni numeriche tridimensionali e condizioni al contorno al pozzo
No full textThe development of a simple closed-form solution for assessing concentration uncertainty in groundwater risk analysis
No full textA simple procedure for the identification of aquifer parameters based on steady pumping tests
No full textConvergent radial transport in three-dimensional heterogeneous aquifers: The impact of the hydraulic conductivity structure
No full textThis paper studies the impact of the hydraulic conductivity structure on solute transport in a radially convergent heterogeneous flow field, which is generated by a well pumping a confined aquifer. The solute is injected instantaneously in a fully penetrating well at a known distance from the pumping well and the analysis is performed numerically by considering four conductivity structures sharing the same two-point statistics, but displaying widely different higher-order moments and connectivity features. The overall objective of the present work is to assess the impact of three-dimensional hydraulic conductivity structures on the Breakthrough Curve (BTC) at a pumping well as a function of a few structural parameters: the logconductivity variance the integral scales along the horizontal and vertical directions, the local-scale dispersivity and the distance of the injection well. The numerical simulations are also compared with two analytical solutions from literature based on the First Order Approximation and the Self Consistent Approximation, respectively. The results indicate that the principal features of the BTC are weakly dependent on the hydraulic conductivity structure, similar to the findings of Janković (2017) for transport in uniform flow. Also, the simple First-Order solution provides a good approximation of the BTC in most of the scenarios considered, and thus it can be a useful and effective tool for screening purposes in applications dealing with aquifers’ contamination
Three-dimensional numerical analysis of steady state pumping tests in heterogeneous confined aquifers
No full textWe study three-dimensional steady state flow field generated by a fully penetrating well extracting a constant water discharge from a confined aquifer of constant thickness. The hydraulic conductivity K is modeled as an axisymmetric, stationary random space function, and the flow equation is solved by using the seven-node finite volume numerical scheme. In view of application in aquifer characterization we analyze how the equivalent conductivity K-eq varies as a function of the distance from the extraction well. The numerical simulations showed that the boundary condition at the well exerts a large impact on K-eq and that the first-order solution in sigma(Y)2 obtained by Indelman et al. (1996) is valid up to sigma(2)(Y) = 0.5. For higher values of sigma(2)(Y) the first-order solution overestimates K-eq with differences that for a given sigma(2)(Y), reduce progressively as the formation becomes more anisotropic. A simple inverse procedure based on K-eq, obtained through cross-well interference, is finally proposed and tested with the objective of estimating the parameters of the geostatistical model of variability of the hydraulic conductivity. A few parametric examples showed that a suitable interpretation of pumping tests can be used to safely estimate parameters such as the geometric mean of the hydraulic conductivity, its variance, and, although with larger uncertainty, the horizontal integral scale, while the inference of the anisotropy ratio is highly uncertain and error prone
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