RESIDENCE TIMES OF KARST CONDUIT HYPORHEIC FLOW

One of the primary causes for dynamic gradients of dissolved chemical constituents in the sediment below streams is hyporheic flow. We present computational fluid dynamics models of bedform driven hyporheic flow in the rock at the margin of a phreatic karst conduit. The modeling includes residence time distributions of water in the hyporheic zone, which can be used to infer chemical gradients. Multiple scales of bedforms yield a distribution of hyporheic residence times. We discuss a dimensionless number characterizing residence time distributions, accounting for geometry and permeability. These results may be important for hyporheic flow in bedrock below thin sediment in streams, and in bedrock streams.