Search results for "Ponding"
showing 10 items of 34 documents
A field assessment of the Simplified Falling Head technique to measure the saturated soil hydraulic conductivity
2012
Abstract The Simplified Falling Head (SFH) technique to measure field saturated soil hydraulic conductivity, Kfs, has received little testing or comparison with other techniques. Different experiments were carried out to i) determine the effect of ring size on the measured conductivity; ii) compare the SFH and Pressure Infiltrometer (PI) techniques in a clay loam soil; and iii) evaluate the approach used in the SFH methodology to estimate the α* parameter. Sampling a relatively large number of sites allowed to detect statistically significant relationships between the Kfs values obtained with rings differing in diameter (0.15 and 0.30 m, respectively). The ring size effect was substantial (…
Soil hydrological response under simulated rainfall in the Dehesa land system (Extremadura, SW Spain) under drought conditions
1998
Soil hydrology was investigated in the Guadelperalon experimental watershed in order to determine the influence of land use and vegetation cover on runoff and infiltration within the Dehesa land system. Five soil–vegetation units were selected: (1) tree cover, (2) sheep trials, (3) shrub cover, (4) hillslope grass and (5) bottom grass. The results of the simulated rainfall experiments performed at an intensity of 56·6 mm h−1 during one hour on plots of 0·25 m2, and the water drop penetration time test indicate the importance of water repellency in the Dehesa land system under drought conditions. Low infiltration rates (c. 9–44 mm h−1) were found everywhere except at shrub sites and in areas…
Influencia de la litología en los procesos de erosión en <i>badlands</i>. Los casos de Anna (Valencia) y Petrer (Alicante)
1997
By means of experiments with simulated rainfall the hydrological and erosional behaviour of degraded surfaces (badlands) developed on two different parent materials (marls and clays) is studied. On the Keuper clays, the ponding (4'07") and runoff (6' 36") initiation is delayed, the infiltration rates (38.63 mm h<sup>-1</sup>) are high, and the runoff coefficient (11.2 % after 30 minutes and 19.4 % after 60 minutes) and the erosion rates (13 g m<sup>2</sup> h<sup>-1</sup>) are low. On the contrary, over Cretaceous marls, the ponding (1’ 37") and the surface runoff (2' 52") initiation is very rapid, the infiltration rates are low (11.2 mm h<sup>-1<…
Asymmetric colour matching: memory matching versus simultaneous matching
2001
We have compared corresponding pairs obtained by simultaneous matching (haploscopic matching) and by memory matching (after 10 min) using 34 reference tests selected from the Munsell Atlas (glossy), belonging to the four main hues 5Y, 5G, 5PB, and 5RP. These colours lie very close to the F1 and F2 axes in the SVF space, where we have analyzed our results. Illuminants D65 and A were used as reference and matching illuminants, respectively. Our results show for both kinds of matching a tendency to select more colourful colours than the original ones, with significant differences between matching and test colours, whereas hue does not seem to follow a definite pattern. This behavior is similar…
Field and Numerical Tests of the Two-Ponding Depth Procedure for Analysis of Single-Ring Pressure Infiltrometer Data
2013
Abstract The two-ponding depth (TPD) analysis procedure of single-ring infiltrometer data can yield invalid results, i.e., negative values of the field-saturated soil hydraulic conductivity or the matric flux potential, denoting failure of the two-level run. The objective of this study was to test the performance of the TPD procedure in analyzing the single-ring infiltrometer data of different types of soils. A field investigation carried out in western Sicily, Italy, yielded higher failure rates (40%) in two clay loam soils than in a sandy loam soil (25%). A similar result, i.e., fine-textured soils yielding higher failure rates than the coarse-textured one, was obtained using numerically …
Testing laboratory methods to determine the anisotropy of saturated hydraulic conductivity in a sandy–loam soil
2009
Abstract Anisotropy, a (the log of the ratio of horizontal to vertical conductivity, log 10 ( K h / K v )), of saturated soil hydraulic conductivity, K s , affects transport processes in soil but is not routinely measured, probably because practical and validated methods are lacking. The objective of this investigation was to determine the effects of different constant-head laboratory and sampling procedures on anisotropy of saturated hydraulic conductivity measurements. The sequence of K s measurements was varied (vertical conductivity, K v , first, then horizontal, K h , second and vice versa) for an experimental set-up considering five variables: 1) water ponding type (Mariotte or siphon…
Relationships between climate and soil hydrological and erosional characteristics along climatic gradients in Mediterranean limestone areas
1998
An investigation was undertaken to determine the relationships between climate and soil hydrological and erosional characteristics. Rainfall simulation experiments were carried out along three climatological gradients on similar limestone lithologies in the Mediterranean region. Standard experiments were used to characterize each site so that an objective comparison could be made. At each of the eleven south-facing slopes three experiments were carried out. A total of 33 plots were selected for the experiments; located in the Galilee and Carmel Mountains (Israel), Crete (Greece) and Alicante (Spain). Simulated rainfall was used in order to measure time to ponding and runoff, steady-state in…
Direct synthesis of pure brannerite UTi2O6
2019
International audience; A new method based on the precipitation of uranium(IV) and titanium(IV) hydroxide precursors was developed to prepare pure brannerite UTi2O6 samples. In fact, U(IV) dissolved in HCl (6 mol L−1) was mixed to Ti (IV) alkoxyde before a basification step with an excess of NH4OH to obtain a highly reactive nanometric (U,Ti)(OH)4 powder. The obtained powder was then dried under vacuum, pressed into pellets and finally fired at 1300 °C. This method led to the formation of pure brannerite in contrast to previous reported protocols, which showed the formation of impurities such us UO2 and TiO2. The refined unit cell parameters of UTi2O6 led to a = 9.8113(2) Å, b = 3.7681(1) Å…
Cultural institutions as agents of urban and community regeneration in the (post-)pandemic city. The case of the «Laboratorio Zen Insieme» in Palermo
2022
Although all cities in the world have been affected by the COVID-19 pandemic, its impacts on the territories, yet to be understood, are unevenly distributed, revealing extremely varied imbalances depending on the places. However, it is clear that the virus and its variants have aggravated pre-existing socio-spatial inequalities, creating new ones and bringing attention back to those implications between space, planning, public health and citizenship that are at the origins of contemporary urbanism. In a reference framework in which the crisis is globalized but unequal and in the absence of a welfare system capable of responding to the urgencies of the most marginalized social contexts and g…
Transfer coefficients for evaporation of a system with a Lennard-Jones long-range spline potential
2007
International audience; Surface transfer coefficients are determined by nonequilibrium molecular dynamics simulations for a Lennard-Jones fluid with a long-range spline potential. In earlier work A. Røsjorde et al., J. Colloid Interface Sci. 240, 355 2001; J. Xu et al., ibid. 299, 452 2006, using a short-range Lennard-Jones spline potential, it was found that the resistivity coefficients to heat and mass transfer agreed rather well with the values predicted by kinetic theory. For the long-range Lennard-Jones spline potential considered in this paper we find significant discrepancies from the values predicted by kinetic theory. In particular the coupling coefficient, and as a consequence the…