Examining the assumptions of the single-porosity archetype for transport in bedrock aquifers

Bedrock aquifers are often characterized using porous medium concepts, but it is unclear to what extent these aquifers comply with the additional assumptions inherent in porous medium models. The core assumption is that aquifers can be treated as continuous single-porosity porous media, with Darcy's law describing the flow. The auxiliary assumptions include that the aquifer framework is insoluble, and that permeability varies randomly in space. The combination of these assumptions is referred to here as the single-porosity archetype. The applicability of the major assumptions to transport in bedrock aquifers was examined by considering substantial data sets for each assumption. It is shown that weathering often substantially increases the permeability in both carbonate and silicate rocks. Nonrandom spatial organization of permeability frequently occurs during deposition and diagenesis of rocks, as bedding planes, fractures zones, and interflow zones. Subsequently, self-organization occurs due to feedbacks between flow and weathering. Bedrock aquifers thus deviate substantially from the assumptions of the single-porosity archetype. The common presence of continuous preferential flow paths shows that bedrock aquifers often behave as dual-porosity aquifers when considering transport.

Automated summary

Bedrock aquifers deviate substantially from the assumptions of the single-porosity archetype and often behave as dual-porosity aquifers. This is because weathering increases permeability in rocks and nonrandom spatial organization of permeability frequently occurs. These deviations and behaviors have important implications for the transport processes in bedrock aquifers.