SEPARATING CHEMICAL AND PHYSICAL EROSION PROCESSES IN FLUVIOKARST: FLUME EXPERIMENTS

Accurate modeling of karst conduit development is predicated on understanding the erosion processes at work. In fluviokarst, where sediment is fluxing through the subsurface carried by pipe full or free surface flows, these processes have chemical and physical components. Flume experiments mimicking high water and sediment flow rates help delineate the range of processes and rates in these systems.

To simulate a mature conduit, a ~60 cm long block of Ordovician Centre Hall limestone was drilled with a 15 cm round conduit. This conduit is well beyond the lower size limit of turbulent flow and sediment transport (1 cm), but small enough to allow analysis and substantial interaction between the sediment and surface. The block was placed in a sediment recirculating flume, and flows of 3 to 4 l/s in the bottom half of the conduit entrained 1-mm sand as bedload in free surface flow. After a 5-day run, the conduit showed wear from the sediment load and water and additional evidence of tooling by sediment. This strongly suggests that with adequate sediment supply physical processes play an important role in conduit development. Further experiments will examine wear patterns and erosion rates under different flow conditions. Additional work on the lab bench and in the field will be required to place this work in the proper context and generate valid erosion rates.