Hydraulic Geometry of Cave Passages

Abstract

There are two competing sets of factors that control the original solutional shapes of the natural drainpipes that make up the conduit system. One set comprises the spatial variations in the rates of solution of the bedrock caused by the distribution and geometry of joints and bedding planes, by the variations in solubility of the limestone, and by the distribution of such lithologic features as shale beds, dolomite beds, sandy layers, and chert nodules. The second set comprises the variations in rates of solution caused by the shifting flow regimes of moving water. If flow velocities are low, the passage tends to be etched into a complex shape controlled by structural and lithologic factors and we speak of an etching geometry or structure-controlled geometry. If the rate of solution varies with flow velocity, the shape of the passages will be modified to accommodate the flow pattern and we speak of a hydraulic geometry. Etching geometries tend to be irregular and angulate; hydraulic geometries tend to be smooth, curvilinear shapes. The forms of solution conduits are further modified by bedrock breakdown, by sediment in-filling, and by the deposition of secondary calcite deposits so that the shapes of cave passages might be quite different from the original solution shapes. Some deduction and interpretation is needed on the part of the karst hydrogeologist.