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.
An understanding of preferential flow in the vadose zone is crucial for the prediction of the fate of pollutants.
Infiltration basins, developed to mitigate the adverse effects of impervious surfaces in urban areas, are established above
strongly heterogeneous and highly permeable deposits and thus are prone to preferential flow and enhanced pollutant
transport. This study numerically investigates the establishment of preferential flow in an infiltration basin in the Lyon
suburbs (France) established over a highly heterogeneous glaciofluvial deposit covering much of the Lyon region. An investigation
of the soil transect (13.5 m long and 2.5 m deep) provided full characterization of lithology and hydraulic
properties of present lithofacies. Numerical modeling with the HYDRUS-2D model of water flow in the transect was
used to identify the effects of individual lithofacies that constitute the deposit. Multiple scenarios that considered different
levels of heterogeneity were evaluated. Preferential flow was studied for several values of infiltration rates applied
after a long dry period. The numerical study shows that the high contrast in hydraulic properties of different lithofacies
triggers the establishment of preferential flow (capillary barriers and funneled flow). Preferential flow develops mainly
for low water fluxes imposed at the surface. The role of individual lithofacies in triggering preferential flow depends on
their shapes (layering versus inclusions) and their sizes. While lenses and inclusions produce preferential flow pathways,
the presence of the surface layer has no effect on the development of preferential flow and it only affects the effective
hydraulic conductivity of the heterogeneous transect.
Artificial basins are used to recharge groundwater and protect water pumping fields. In these basins, infiltration
rates are monitored to detect any decrease in water infiltration in relation with clogging. However, miss-estimations
of infiltration rate may result from neglecting the effects of water temperature change and air-entrapment. This study
aims to investigate the effect of temperature and air entrapment on water infiltration at the basin scale by conducting successive
infiltration cycles in an experimental basin of 11869 m2 in a pumping field at Crepieux-Charmy (Lyon, France).
A first experiment, conducted in summer 2011, showed a strong increase in infiltration rate; which was linked to a potential
increase in ground water temperature or a potential dissolution of air entrapped at the beginning of the infiltration. A
second experiment was conducted in summer, to inject cold water instead of warm water, and also revealed an increase
in infiltration rate. This increase was linked to air dissolution in the soil. A final experiment was conducted in spring with
no temperature contrast and no entrapped air (soil initially water-saturated), revealing a constant infiltration rate. Modeling
and analysis of experiments revealed that air entrapment and cold water temperature in the soil could substantially
reduce infiltration rate over the first infiltration cycles, with respective effects of similar magnitude. Clearly, both water
temperature change and air entrapment must be considered for an accurate assessment of the infiltration rate in basins.