Saturation state of fractures in a three-dimensional stochastic network created using chalk interfluve fracture data. A general infiltration boundary (1mm/hr) is applied on the upper slope while the phreatic surface is held at surface on the right hand side. Sufficient water is entering the system to allow the creation of a seepage face on the slope. Dark blue fractures are saturated, white are unsaturated while pale blue fractures contain a free surface. Provided by Alex Bond.

NAPSAC has been extended to allow the solution of flow and transport in discrete fracture networks under phreatic conditions.

 
The flow solutions to the non-linear equations are obtained with a very efficient solution algorithm using Newton-Raphson linearisation. Unsaturated flow is characterised by a simple capillary curve model, the objective being to represent the specific yield of the aquifer and flow beneath the moving phreatic surface. Non-linear boundary conditions and a full borehole model have also been included to provide a more comprehensive flow simulation. A simple equivalent matrix is incorporated to allow modelling of units where dual permeability and dual porosity are significant.
Verification has been performed using field fracture data from the Southern Chalk of the UK, provided by the British Geological Survey.

This project has been performed in collaboration with the School of Earth Sciences of the University of Birmingham and is part of Alex Bond's PhD.

Tracks of 100 particles injected at inflow points on the slope, coloured with time. Colours blend from brown (early time), through to late (dark blue). Note irregular, three-dimensional nature of particle paths even within a scenario that forces bulk two-dimensional flow. Provided by Alex Bond.