1,721,030 research outputs found
WATER-SEDIMENT THERMAL INTERACTION IN A LAGOON EXCHANGING WATER WITH THE SEA (WINTER CASE)
No full textIn this paper the thermal behaviour of both a shallow and well-mixed layer of water and its underlying sediment (e.g. a lagoon) is described. The water-sediment thermal interaction is analytically obtained by assuming a sinusoidal trend for the water depth. During the first half-period, the water leaves the lagoon at temperature T(t) and in the second half-period the water comes back but at a constant temperature T*. In this study theoretical results in a case without the solar flux will be shown (i.e. the case corresponds to a typical winter case)
ANNUAL SOIL-TEMPERATURE EVOLUTION
No full textA model to study the annual behaviour of the temperature of a homogeneous solid (considered like a semispace) will be presented in this paper. The model gives the temperature of the solid at any time and at any depth. It assumes the solar flux as the incoming flux, constant atmospheric effects and a simple expression for the outgoing flux. Finally solutions of the soil temperature, when a meteorological transient (box shape) is present, will be shown. The model gives a qualitative behaviour of the soil temperature on a yearly basis and it is like the many experimentally observed behaviours
Confined Diffusion
No full textAn equation for the unidimensional confined diffusion is proposed. The equation coincides with the well-known homogeneous equation except the presence of a source term. This term which has the form of a dipole distribution is located on a moving front which sharply separates two distinct regions. In the first region (from the boundary up to the front) the confined solution coincides with a suitable solution of the homogeneous equation; in the second region (besides the front) it vanishes. The source term, moreover, switches off the diffusing flux at the front. The sharp confinement allows to relax the original boundary conditions of the homogeneous equation. Precisely, to the function depending on the time at the boundary, another arbitrary function depending on the space at the initial time is added. This new function (provided not vanishing) allows to obtain in general an acceptable evolution of the front and does not prevent the validity of the conservation law: flux at the boundary is equal to the time variation of the diffusing quantity contained between the boundary and the front. By a suitable choice of this new function, so that it results to be connected to the other boundary condition (that depending on time) it is possible to arrive at an evolution of the front such as: lÖ{4Kt}\lambda \sqrt {4Kt} , where λ,K, corresponding, respectively, to a dimensionless parameter and diffusivity, depend on the medium. Under such simplifying assumption, it is possible to obtain an analytical expression for the confined solution. This solution, evaluated in a point of the space, arrives asymptotically at the same value reached by the solution of the homogeneous equation
TIME SERIES OF SOIL WATER CONTENT MEASUREMENTS IN THE TARO RIVER GIANT ALLUVIAL FAN
No full textThe soil water content profile in the surface soil has been measured at two stations located between the town of Parma and the Taro River (Po valley) for few years. At one of the two stations, some meteorological data are also collected, including air temperature and relative humidity at two levels besides atmospheric pressure and precipitation. The soil water content measurements are performed with Frequency Domain Reflectometry (FDR) sensors; the scaled frequencies and the meteorological data are automatically collected and stored in a data logger and then transmitted when required. The aim is to study the partition of the water entering the surface of the soil in: evaporation, run off, water stored in the measured soil column and percolation towards the deeper layers. The readings show a clear dependence on the soil depth; a high variability characterizes the superficial probes while the deeper ones show smoother trends. Due to the reduced precipitation during 2008 summer-autumn seasons, the soil water content at 1.5 m reached the maximum value measured the previous year only about at the middle of January. Vice versa, the soil water content at 2 m depth never reached the previous winter value; it had its maximum in February. During some drying periods, a linear trend of the soil water content well represents the measurements collected at the shallowest levels. These data also show a daily oscillation damping with the depth. A new hydrological station is going to be installed very close to the Taro River. Moreover, the meteorological station, located in the Enia area of the well #1 of Roncopascolo, is now completed with new sensors, which permit to compute all the terms of the energy balance equation required to estimate the evaporation into the atmosphere
Analytical solutions of the linearized Richards equationwith flux boundary conditions for a half space and afinite layer
No full textA useful insight of physical mechanisms related to the complex hydrological problems can be provided by analytical solutions of differential flow equations (e.g. Richards equation). Although analytical solutions may be not suitable to solve complex hydrological problems, they are fast and useful to test numerical procedures. The aim of this work is the study of the water flow in a sub-surface unsaturated layer (Vadose zone).In this context, the linearized Richards equation is analytically solved for arbitrary flux boundary conditions and arbitrary soil moisture initial conditions. Approximating the supplementary conditions by step-wise functions, the solution results a sumof solutions obtained for constant boundary conditions. This approach is quite useful because it permits to use standard meteorological data as boundary conditions. In fact, it can be used precipitation data as incoming flux and evaporation from Bowen ratio data as outgoing flux; these data are very common, while soil volumetric water content measurements are usually not available exactly at the soil-atmosphere interface. The study is extended to a finite layer schematisation, which can represent a real situation, in case of a shallow water table. The aforementioned solutions hold till the saturation is reached; after saturation behaviour is under study
General analytical solutions of the linearized Richards equation for a half-space and a finite-thickness domain
No full textThis paper aims to describe a compilation of solutions of the linearized one-dimensional Richards equation, solved both in a half-space and in a finite-thickness domain. The solution (the soil water content at any time and depth) can be represented as the sum of two components, one related to the initial condition and to null boundary conditions and the other related to the boundary conditions and to a null initial condition. The sum of the two quoted components is the general solution of the Richards equation in integral form; the analytical expression of the soil water content distribution is therefore obtained if the integrals in the solution can be solved. Besides the integral form solution, another solution holding for any initial and boundary conditions represented with step functions is described in the paper. The initial condition is always the soil water content profile (e.g. the one experimentally measured) while the boundary conditions are different for the two domains. For the half-space domain, the boundary condition can be the soil water content at the surface or the surface flux (e.g. the measured precipitation or evaporation). For this domain, the solution, with the initial-boundary conditions expressed as step functions, is obtained using a procedure, which accounts for the effects of the hydrological conditions of the soil on the flux at the surface. Therefore, this procedure is able to switch between successive atmosphere-controlled and soil-controlled phases of infiltration or evaporation, as required by the given boundary condition. The procedure provides the ponding time, the desiccation time and the surface water flux during the soil-controlled phases. For the finite-thickness domain, the top and bottom boundary conditions are given as time dependent soil water content trends. Also for the finite-thickness domain, a solution, obtained approximating the initial-boundary conditions with step functions, is derived using the basic solution. It provides the soil water content profile evolution, the top and bottom instantaneous and cumulative fluxes and the water gained by the soil layer in a specified time interval. Lastly, a comparison between the procedure results and an exact analytical solution is discussed
HYDROMETEOROLOGICAL MEASUREMENTS IN THE TARO RIVER GIANT ALLUVIAL FAN
No full textIn the framework of the National Project: “Esplorazione geofisica e geologica di alcuni complessi acquiferi alluvionali nella pianura Padana tra Milano e Bologna, per la modellazione della circolazione idrica sotterranea”, the soil water content profile in the surface soil is measured at two stations located between the town of Parma and the Taro River (Po valley). The physical structure of the Taro River giant alluvial fan is well known because of the previous studies of the University of Parma geologists involved in the same National Project. On the basis of this knowledge, one station was installed at the site of the well #1 of Roncopascolo and the other at a site closer to the Taro River (Barilla field). At Roncopascolo, meteorological data are also collected, including air temperature and relative humidity at two levels, while, at Barilla field, only the soil moisture profile is measured. The aim is to study the partition of the water entering the surface of the soil in: evaporation, run off, water stored in the measured soil column and percolation towards the deeper layers. The soil water content measurements are performed with Frequency Domain Reflectometry (FDR) sensors; the scaled frequencies and the meteorological data are automatically collected and stored in a data logger and then transmitted when required. Roncopascolo station started at the end of July 2006, while Barilla station started in October 2006. At both stations, soil samples were taken for the laboratory determination of the soil physical characteristics. The time variation of the water stored in the studied soil columns is estimated by means of the mass balance method. From the data collected in the summer period, the evaporation is estimated. Similarly, applying the mass balance method to the data collected during and after heavy precipitation events, the water infiltrated into the soil can be estimated. Furthermore, the time evolution of the soil moisture profile is studied solving the linearized one-dimensional Richards equation for discrete arbitrary initial and boundary conditions. The results are the soil water content at any required time and depth in a semi-infinite unsaturated porous medium domain, the ponding time, the desiccation time and the surface water flux during the soil-controlled phases of infiltration or evaporation
Analytical solutions of the linearized Richards equationfor arbitrary surface boundary conditions andarbitrary initial conditions
No full textUnsaturated flow processes are subject to either atmosphere control or soil control, often switching from one to the other. In order to study the water flow in a sub-surface unsaturated layer, the linearized Richards equation is analytically solved for arbitrarysurface boundary conditions and arbitrary soil moisture initial conditions. Approximating the supplementary conditions by step-wise functions, the solution results a sum of solutions obtained for constant boundary conditions. This approach is quite useful because it permits to use standard meteorological data as boundary conditions. In fact, precipitation data can be used as incoming flux and evaporation data (Bowen ratio) as outgoing flux. Meteorological data are very common, while soil volumetric water content measurements, excluding saturation and air dry soil, are usually not available exactly at the soil-atmosphere interface. The procedure proposed in this work automaticallyswitches from flux boundary conditions to soil moisture boundary conditions accounting for atmosphere controlled or soil controlled evaporation or infiltration
ANALYSIS OF THE SOIL MOISTURE BEHAVIOUR DURING WETTING AND DRYING EPISODES FROM TDR DATA COLLECTED AT PALLANZENO (TOCE VALLEY)
No full texthttp://www.map.meteoswiss.ch/map-doc/NL15/menziani.pd
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