An electrical analog study of the geometry of limestone solution

Abstract

This study of the geometry of limestone solution is based on the following conditions: (1) the limestone is impermeable but contains and transmits water in joints, fractures, bedding‐plane partings, and solution channels; (2) at depth, the limestone aquifer is underlain by impermeable rock; (3) ground water in the limestone is under water‐table conditions; (4) recharge to the limestone is by infiltration of precipitation through the overlying rock to the zone of saturation; (5) discharge from the aquifer is by seeps and springs; and (6) ground water dissolves the limestone through which it flows, continuously modifying the flow pattern and the hydrologic properties of the medium. These conditions commonly are found in limestone terranes in the eastern and central United States. An electrical analog was constructed conforming to this description of the ground‐water flow system and has been used to define the pattern, velocity, and density of ground‐water flow and the relative length of time of contact of water with the aquifer. Successive models are used to illustrate progressive limestone solution and changes in ground‐water flow in the aquifer. The initial analog indicates a strongly convex water table with the greatest density of flow at shallow depths beneath the water table near the point of discharge. Successive models indicate greater concentration of flow near and on the level of ground‐water discharge, an overall lowering of the water table, and a pronounced flattening of the water table near the discharge point. Results of the analog study support the following conclusions: (1) The most active zone of solution is at shallow depths beneath the water table and near the point of ground‐water discharge. Consequently, the size of channels generally decreases with depth and increases with proximity to the point of ground‐water discharge. (2) Generally, solution channels have a greater lateral than vertical extent.