A large single-ring infiltrometer test was performed in order to characterize the saturated hydraulic conductivity
below an infiltration basin in the well field of Lyon (France). Two kinds of data are recorded during the experiment:
the volume of water infiltrated over time and the extension of the moisture stain around the ring. Then numerical
analysis was performed to determine the saturated hydraulic conductivity of the soil by calibration.
Considering an isotropic hydraulic conductivity, the saturated hydraulic conductivity of the alluvial deposits is estimated
at 3.8 10–6 m s–1. However, with this assumption, we are not able to represent accurately the extension of the moisture
stain around the ring. When anisotropy of hydraulic conductivity is introduced, experimental data and simulation results
are in good agreement, both for the volume of water infiltrated over time and the extension of the moisture stain.
The vertical saturated hydraulic conductivity in the anisotropic configuration is 4.75 times smaller than in the isotropic
configuration (8.0 10–7 m s–1), and the horizontal saturated hydraulic conductivity is 125 times higher than the vertical
saturated hydraulic conductivity (1.0 10–4 m s–1).
In Mediterranean ecosystems, special attention needs to be paid to forest–water relationships due to water
scarcity. In this context, Adaptive Forest Management (AFM) has the objective to establish how forest resources have to
be managed with regards to the efficient use of water, which needs maintaining healthy soil properties even after
disturbance. The main objective of this investigation was to understand the effect of one of the AFM methods, namely
forest thinning, on soil hydraulic properties. At this aim, soil hydraulic characterization was performed on two
contiguous Mediterranean oak forest plots, one of them thinned to reduce the forest density from 861 to 414 tree per ha.
Three years after the intervention, thinning had not affected soil water permeability of the studied plots. Both ponding
and tension infiltration runs yielded not significantly different saturated, Ks, and unsaturated, K–20, hydraulic conductivity
values at the thinned and control plots. Therefore, thinning had no an adverse effect on vertical water fluxes at the soil
surface. Mean Ks values estimated with the ponded ring infiltrometer were two orders of magnitude higher than K–20
values estimated with the minidisk infiltrometer, revealing probably soil structure with macropores and fractures . The
input of hydrophobic organic matter, as a consequence of the addition of plant residues after the thinning treatment,
resulted in slight differences in terms of both water drop penetration time, WDPT, and the index of water repellency, R,
between thinned and control plots. Soil water repellency only affected unsaturated soil hydraulic conductivity
measurements. Moreover, K–20 values showed a negative correlation with both WDPT and R, whereas Ks values did not,
revealing that the soil hydrophobic behavior has no impact on saturated hydraulic conductivity.
Isothermal and non-isothermal infiltration experiments with tracer breakthrough were carried out in the laboratory
on one intact column (18.9 cm in diameter, 25 cm in height) of sandy loam soil. For the isothermal experiment, the
temperature of the infiltrating water was 20°C to the initial temperature of the sample. For the two non-isothermal experiments
water temperature was set at 8°C and 6°C, while the initial temperature of the sample was 22°C. The experiments
were conducted under the same initial and boundary conditions. Pressure heads and temperatures were monitored in two
depths (8.8 and 15.3 cm) inside the soil sample. Two additional temperature sensors monitored the entering and leaving
temperatures of the water. Water drained freely through the perforated plate at the bottom of the sample by gravity and
outflow was measured using a tipping bucket flowmeter. The permeability of the sample calculated for steady state stages
of the experiment showed that the significant difference between water flow rates recorded during the two experiments
could not only be justified by temperature induced changes of the water viscosity and density. The observed data
points of the breakthrough curve were successfully fitted using the two-region physical non-equilibrium model. The results
of the breakthrough curves showed similar asymmetric shapes under isothermal and non-isothermal conditions.
When dealing with groundwater resources, a better knowledge of the hydrological processes governing flow
in the unsaturated zone would improve the assessment of the natural aquifer recharge and its vulnerability to contamination.
In North West Europe groundwater from unconfined chalk aquifers constitutes a major water resource, therefore the
need for a good hydrological understanding of the chalk unsaturated zone is essential, as it is the main control for aquifer
recharge. In the North Paris Basin, much of the recharge must pass through a regional chalk bed that is composed of a
porous matrix with embedded fractures. The case study regards the role of the thick unsaturated zone of the Cretaceous
chalk aquifer in Picardy (North of France) that controls the hydraulic response to rainfall. In order to describe the flow
rate that reaches the water table, the kinematic diffusion theory has been applied that treats the unsaturated
water flow equation as a wave equation composed of diffusive and gravitational components. The kinematic diffusion
model has proved to be a convenient method to study groundwater recharge processes in that it was able to provide a
satisfactory fitting both for rising and falling periods of water table fluctuation. It has also proved to give an answer to
the question whether unsaturated flow can be described using the theory of kinematic waves. The answer to the question
depends principally on the status of soil moisture. For higher values of hydraulic Peclet number (increasing saturation),
the pressure wave velocities dominate and the preferential flow paths is provided by the shallow fractures in the vadose
zone. With decreasing values of hydraulic Peclet number (increasing water tension), rapid wave velocities are mostly due
to the diffusion of the flow wave. Diffusive phenomena are provided by matrix and fracture-matrix interaction.
The use of a kinematic wave in this context constitutes a good simplified approach especially in cases when there is a
lack of information concerning the hydraulic properties of the fractures/macropores close to saturation.
Two sets of triangular hydrographs were generated in a 12-m-long laboratory flume for two sets of initial bed conditions: intact and water-worked gravel bed. Flowrate ranging from 0.0013 m3 s–1 to 0.0456 m3 s–1, water level ranging from 0.02 m to 0.11 m, and cumulative mass of transported sediment ranging from 4.5 kg to 14.2 kg were measured. Then, bedload transport rate, water surface slope, bed shear stress, and stream power were evaluated. The results indicated the impact of initial bed conditions and flow unsteadiness on bedload transport rate and total sediment yield. Difference in ratio between the amount of supplied sediment and total sediment yield for tests with different initial conditions was observed. Bedload rate, bed shear stress, and stream power demonstrated clock-wise hysteretic relation with flowrate. The study revealed practical aspects of experimental design, performance, and data analysis. Water surface slope evaluation based on spatial water depth data was discussed. It was shown that for certain conditions stream power was more adequate for the analysis of sediment transport dynamics than the bed shear stress. The relations between bedload transport dynamics, and flow and sediment parameters obtained by dimensional and multiple regression analysis were presented.
Topsoil field-saturated hydraulic conductivity, Kfs, is a parameter that controls the partition of rainfall between
infiltration and runoff and is a key parameter in most distributed hydrological models. There is a mismatch between the
scale of local in situ Kfs measurements and the scale at which the parameter is required in models for regional mapping.
Therefore methods for extrapolating local Kfs values to larger mapping units are required. The paper explores the feasibility
of mapping Kfs in the Cévennes-Vivarais region, in south-east France, using more easily available GIS data
concerning geology and land cover. Our analysis makes uses of a data set from infiltration measurements performed in
the area and its vicinity for more than ten years. The data set is composed of Kfs derived from infiltration measurements
performed using various methods: Guelph permeameters, double ring and single ring infiltrotrometers and tension infiltrometers.
The different methods resulted in a large variation in Kfs up to several orders of magnitude. A method is proposed
to pool the data from the different infiltration methods to create an equivalent set of Kfs. Statistical tests showed
significant differences in Kfs distributions in function of different geological formations and land cover. Thus the mapping
of Kfs at regional scale was based on geological formations and land cover. This map was compared to a map based
on the Rawls and Brakensiek (RB) pedotransfer function (mainly based on texture) and the two maps showed very different
patterns. The RB values did not fit observed equivalent Kfs at the local scale, highlighting that soil texture alone is
not a good predictor of Kfs.
Differences in soil stability, especially in visually comparable soils can occur due to microstructural processes and interactions. By investigating these microstructural processes with rheological investigations, it is possible to achieve a better understanding of soil behaviour from the mesoscale (soil aggregates) to macroscale (bulk soil). In this paper, a rheological investigation of the factors influencing microstructural stability of riparian soils was conducted. Homogenized samples of Marshland soils from the riparian zone of the Elbe River (North Germany) were analyzed with amplitude sweeps (AS) under controlled shear deformation in a modular compact rheometer MCR 300 (Anton Paar, Germany) at different matric potentials. A range physicochemical parameters were determined (texture, pH, organic matter, CaCO3 etc.) and these factors were used to parameterize pedotransfer functions.
The results indicate a clear dependence of microstructural elasticity on texture and water content. Although the influence of individual physicochemical factors varies depending on texture, the relevant features were identified taking combined effects into account. Thus, stabilizing factors are: organic matter, calcium ions, CaCO3 and pedogenic iron oxides; whereas sodium ions and water content represent structurally unfavorable factors. Based on the determined statistical relationships between rheological and physicochemical parameters, pedotransfer functions (PTF) have been developed.