Abstract:

Three conceptual models are proposed for the integration of the large systems of conduits responsible for groundwater flow in soluble rocks. These models are supported by laboratory experiments with scaled solution models, flow-field analogues, and evidence from existing caves.
The three models reflect different boundary conditions imposed by geologic structure and stratigraphy. They have three characteristics in common. First, the smaller elements of the larger systems propagate separately from points of groundwater input toward points of discharge as distributary networks. Second, the integration of the smaller networks proceeds headward from the resurgence, in a stepwise fashion. Third, the result of the integration process in each case is a tributary system with many inputs discharging through a single discharge point.
The potential for growth of each of the smaller networks, within a common pressure field, is related to its distance from the discharge boundary and the distribution of other inputs. The first input to establish a low-resistance link to the discharge boundary will effect a localized depression within the potential field, thus attracting the flow and redirecting the growth of nearby networks until they eventually link with it. As additional orders of links develop, the system takes on a tributary pattern.
The first model applies to steeply dipping rocks. Inputs occur where bedding planes are truncated by erosion, and discharge takes place to the strike. Conduits in this case evolve as a roughly rectangular grid of strike and dip oriented elements. Dip elements are the initial form, with subsequent integration along the strike. The type example is the Holloch in Switzerland.
The second model applies to flat-lying rocks. Inputs occur over a broad area, and discharge takes place along a linear boundary. Conduits in this case evolve in a trellised array with elements normal to the discharge boundary predating those parallel to it. These latter conduits integrate the flow. The type example is the Mammoth Cave Region, Kentucky.
The third model applies to simple systems which occur beneath an impermeable cap rock. Inputs occur where erosion has breached the capping beds. The type example is Cave Creek, Kentucky.