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.
The decline in groundwater levels is a cause of concern in many regions of the world, including the Sand Ridge of Hungary. The causes of the regional depletion range from rising air temperatures, changes in precipitation, domestic and agricultural groundwater use and past amelioration and recent afforestation, including the effects of drilling for crude oil exploration. The relations between the decline, the soil water regime and groundwater recharge under existing aged forests remained unclear thus far. Based on our monitoring of groundwater and soil moisture we aim to clarify this interplay in a new experimental site on the hilltop of the Sand Ridge. We compared three land-uses: a 41-year-old black locust (Robinia Pseudoacacia) offshoot forest, an 83-year-old first generation black pine (Pinus nigra) forest, and a grassland control site. The observed differences in the soil moisture profiles and dynamics were connected to the use of water by the given type of vegetation. We indicated a connection between the disruption of the groundwater recharge and the loss of contact of the rooting system of the forests with the deepening of the unconfined aquifer. Even if the aged forests could locally contribute to the decline, we conclude that the decline at the hilltop site that may be more strongly driven by other regional factors.