1,721,341 research outputs found
Modeling water flow and solute transport in alluvial sediments : scaling and hydrostratigraphy from the hydrological point of view
No full textJoining modelling water flow and solute transport in alluvial sediments with hydrostratigraphy : scales issues
No full textIdentifiability of distributed physical parameters in diffusive-like systems
No full textModelling of 1D diffusive-like systems leads to a parabolic partial differential equation. Since it is usually difficult to measure the physical parameters of the system (a and b), whereas it is easier to measure u (potential) and f (source term), a and b are deduced from u and f by solving an ill-posed inverse problem. The physical parameters are said to be identifiable if different parameter distributions correspond to different potential distributions. Identifiability is equivalent to the uniqueness of the solution of the inverse problem in its direct formulation
A result concerning identifiability of the inverse problem of groundwater hydrology
No full textThe inverse problem of hydrology, namely finding the transmissivity, a, given the piezometric head, u, and source or sink term, f, is herein considered. The concept of identifiability and its links with the uniqueness of the solution of the inverse problem are studied. When u in H1( Omega ) has a piecewise continuous derivative a necessary and sufficient condition for a to be identifiable is stated and proved. Some interesting examples concerning this theorem are presented
Fast representation of dipole-dipole geoelectrical data with pseudosections for regional surveys
No full textI propose a fast method for constructing pseudosections of apparent resistivity from geoelectrical data collected for deep studies with continuous polar dipole-dipole arrays. Once a vertical section is fixed, each value of apparent resistivity is assigned to a point on the section and finally pseudosections are obtained by interpolation. This allows the geophysicist to represent a large amount of data in a fast and simple way, to perform a qualitative interpretation and to facilitate the quantitative interpretation
Modeling Water Flow in Variably Saturated Porous Soils and Alluvial Sediments
Full text linkThe sustainable exploitation of groundwater resources is a multifaceted and complex problem, which is controlled, among many other factors and processes, by water flow in porous soils and sediments. Modeling water flow in unsaturated, non-deformable porous media is commonly based on a partial differential equation, which translates the mass conservation principle into mathematical terms. Such an equation assumes that the variation of the volumetric water content (θ) in the medium is balanced by the net flux of water flow, i.e., the divergence of specific discharge, if source/sink terms are negligible. Specific discharge is in turn related to the matric potential (h), through the non-linear Darcy–Buckingham law. The resulting equation can be rewritten in different ways, in order to express it as a partial differential equation where a single physical quantity is considered to be a dependent variable. Namely, the most common instances are the Fokker–Planck Equation (for θ), and the Richards Equation (for h). The other two forms can be given for generalized matric flux potential (Φ) and for hydraulic conductivity (K). The latter two cases are shown to limit the non-linearity to multiplicative terms for an exponential K-to-h relationship. Different types of boundary conditions are examined for the four different formalisms. Moreover, remarks given on the physico-mathematical properties of the relationships between K, h, and θ could be useful for further theoretical and practical studies
Simulazione mediante modello numerico di un sistema acquifero multistrato che alimenta una centrale di pompaggio dell'Acquedotto di Milano
No full textStudio delle caratteristiche delle equazioni di flusso e trasporto nei mezzi porosi con l’utilizzo dell’analisi spettrale
No full textExperimental and modeling study of the soil-atmosphere interaction and unsaturated water flow to estimate the recharge of a phreatic aquifer
No full textThe aquifer system, which is the resource of water for the city of Milano (Italy), is a multilayered aquifer, characterized by sandy and sandy-gravel units, connected by discontinuous aquitards. The recharge area of the phreatic aquifer is close to the prealpine area, some tens of kilometers north of the city; nevertheless the local recharge given by rain infiltration through the soil is not negligible and contributes to the mass balance of the aquifer. A field campaign was carried out for 16 months in the suburban area of the Lambro Park to evaluate the local recharge due to the rainfall infiltration through the unsaturated zone; the water table in this area lies about 15 m below the ground surface. Standard meteorological data (atmospheric pressure, rainfall, humidity, wind velocity and air temperature) were collected, along with incident and net radiation, to evaluate potential and actual evaporation from the bare soil using three methods (Bowen ratio, Penman, and Hamon equations). Simultaneously, the volumetric soil water content at different depths (down to 76 cm) was measured with time domain reflectrometry probes. A finite-difference model, which solves the one-dimensional Richards equation in transient conditions, was developed to simulate the flow through the unsaturated zone, to evaluate the characteristic time of recharge and the mass balance. The water flow rate through the ground surface was assigned as the upper boundary condition and was evaluated from the mass and energy balance at the atmosphere–soil interface with different approaches based on the meteorological data and the actual soil water content. The lower boundary condition is given by the saturation condition at the water table. Characteristic retention curves were estimated in laboratory using Richards apparatus. In order to calibrate the model, the numerical results were compared with experimental data for two different periods: A dry period (July 2001) and a wet period (October 2001). Finally, the calibrated model was used to simulate the infiltration and the flow through the unsaturated zone for a 15-year-long period (1988–2003) and to estimate the total phreatic aquifer recharge. Moreover, the time lag between a variation of the infiltration/exfiltration rate and the corresponding variation of the recharge rate was evaluated; the values of the delay time of recharge are longer than those computed with models that approximate the transmission zone as a unique cell
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