Monitoring tracer stones through the potholes of Fall Creek Gorge near Williamsport, Indiana

Abstract

We document coarse sediment transport through Fall Creek Gorge, a bedrock channel step-pool system with deep and complex pothole structures located in western Indiana. Tracer clasts are embedded with Passive Integrated Transponder (PIT) tags using our new highly successful and efficient method for drilling holes into small (~ 10 mm) clasts. Repeated surveys of bed topography record deposition and erosion of sediment within potholes. Tracer clasts introduced upstream of the potholes were transported through the reach over a period of a few weeks: we see no evidence for individual coarse sediment particles having long residence times within potholes. Initial transport of tracer clasts was accompanied by a spatially extensive aggradational event. We develop a conceptual model for coarse sediment transport within Fall Creek gorge in which potholes are filled with fine sediment (sand and gravel) prior to initiation of coarser sediment transport. The fine sediment creates a temporary bridge allowing coarse particle to move through the reach without becoming trapped within potholes. We are in the early developmental stages for testing this model in a flume.