Conduit evolution in deep-seated settings: Conceptual and numerical models based on field observations

To examine the interrelation between hydrogeological environment and conduit development in deep-seated settings, a conceptual model is tested by numerical modeling. Based on field observations, simplified model settings are designed and crucial parameters are varied. A coupled continuum-pipe flow model is employed for simulating conduit development within the soluble unit of a multilayer aquifer system. In agreement with field observations, the evolving cave patterns are characterized by pronounced horizontal passages and multiple vertical conduits at the bottom of the soluble unit but only few at the top. The frequency distribution of conduit diameters is found to be bimodal if the permeability of the rock formation is sufficiently high to allow competitive conduit development governed by the feedback between increasing flow and dissolution rates. This feedback, however, is suppressed in low-permeability formations. As a consequence, conduit development is uniform rather than competitive.