See more from this Division: Topical Sessions
See more from this Session: Innovative Methods for Investigating Flow and Transport in Karst Systems I
Abstract:
To describe the flow in the matrix and the conduits we use respectively the Richard's equation and the diffusive wave equation. When discretised, these equations can be combined into a single matrix system. This strategy is also often used in coupled river-aquifer models.
For the diffusive wave equation there exists a special positivity preserving scheme. We show that this scheme does not only preserve positivity but also allows the simulation of steady state, free-surface flows without any restriction on the time step size. This scheme results in a better efficiency of the coupled model. Typically, the steep hydraulic gradients in the conduits disappear faster then those in the matrix. Consequently, a simulation may contain a relatively long time period during which an almost steady state conduit flow is coupled with a transient matrix flow.
It is shown that the common node approach and dual node approach as used in existing discrete-continuum models for karst aquifers are inappropriate. Instead a special dual node approach as commonly used in well-aquifer models should be used. Using this approach the exchange parameter depends on the wetted surface of the conduit, the conductivity of the matrix and the spatial discretisation of the matrix.
The positivity preserving scheme and the special dual node approach may also be useful for coupled river-aquifer models.
See more from this Division: Topical Sessions
See more from this Session: Innovative Methods for Investigating Flow and Transport in Karst Systems I