Paper No. 92-7
Presentation Time: 10:00 AM
A SIMPLE COMPUTER MODEL FOR PARAGENETIC GALLERY FORMATION
Computer models of speleogenesis have primarily been limited to the pre-breakthrough stage, before the onset of turbulent flow. With the onset of turbulent flow speleogenesis is more complex, and thus modeling must take into account factors such as sediment transport. The lack of such models limits the simulation of passage morphologies, such as those caused by paragenesis. Previous models of paragenesis have included a conceptual model and hardware modeling, which demonstrated the formation of paragenetic speleogens, but have not captured the dynamics affecting the formation of paragenetic galleries. Here we use a cross-section evolution model based on a simple method for calculation of boundary shear stress and alluviation, combined with a dissolution rate proportional to shear stress to simulate the formation of paragenetic galleries. Simulation demonstrates dynamics hypothesized in the conceptual model: passage growth starts from a small cross-sectional area, sediment armors the floor and walls as shear stress lowers, causing cross-sectional area to decrease and thus increasing shear stress. This process continues in a loop, driving passage growth upwards, with average velocity, sediment transport capability, and water filled cross-sectional area oscillating around an equilibrium point. The model reveals that paragenesis requires that dissolution rates vary as a function of shear stress to maintain a constant width as seen in field examples. Equilibrium widths depend strongly on discharge and sediment supply.