<abstract xmlns="http://www.w3.org/1999/xhtml"><p>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.</p><p>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.</p></abstract>

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.

Kinematic diffusion approach to describe recharge phenomena in unsaturated fractured chalk

United Kingdom of Great Britain and Northern Ireland

Aerospace & Civil Engineering - Brunel University London

Journal of Hydrology and Hydromechanics

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

When dealing with groundwater resources, a better knowledge of the hydrological processes governing flow in the unsaturated zone would improve the assessment...

Kinematic diffusion approach to describe recharge phenomena in unsaturated fractured chalk

Published Online: Jul 22, 2017

Page range: 287 - 296

Received: Jul 26, 2016

Accepted: May 24, 2017

DOI: https://doi.org/10.1515/johh-2017-0033

Keywords
Unsaturated, Recharge, Rainfall, Chalk, Kinematic, Diffusive

© 2017 Nicola Pastore et al., published by De Gruyter Open

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Kinematic diffusion approach to describe recharge phenomena in unsaturated fractured chalk

Published Online: Jul 22, 2017

Page range: 287 - 296

Received: Jul 26, 2016

Accepted: May 24, 2017

DOI: https://doi.org/10.1515/johh-2017-0033

KeywordsUnsaturated, Recharge, Rainfall, Chalk, Kinematic, Diffusive

© 2017 Nicola Pastore et al., published by De Gruyter Open

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Keywords
Unsaturated, Recharge, Rainfall, Chalk, Kinematic, Diffusive