Author(s): Aaron I. Packman
Linked Author(s):
Keywords: Bedforms; Stream-subsurface exchange; Pumping; Solute transport
Abstract: Flume experiments have demonstrated that stream flow over bedforms generates a significant advective subsurface flow and a corresponding exchange of stream-and subsurface-water. Calculated pore-water velocity profiles have been used to predict the exchange of conservative solutes with deep and shallow sand beds. In this investigation, a new dimensionless parameter scaling is developed in order to obtain a universal solution for solute exchange with beds of any depth. The bed depth affects exchange in two ways: the presence of an impermeable boundary at the bottom of the bed compresses the advective pore-water velocity profile and decreases the stream-subsurface exchange, and the defined reservoir of water in a finite bed imposes a dilution limit on the exchange of a conservative solute from the stream to the bed. The use of a new dimensionless time and exchange parameter allows a single dimensionless curve to represent exchange with any stream and bed depths. The exchange time scale is similar to that for infinite beds, but is decreased (slower exchange for same bedform shape and stream conditions) due to reduced subsurface velocities. The appropriate dimensionless exchange parameter for a finite stream bed is the exchange length scale divided by the bed depth, where the exchange length scale is the average solute penetration into the bed. This new dimensionless exchange parameter is equivalent to the fraction of the bed that has been exchanged. When expressed using these dimensionless parameters, existing experimental data for conservative solute exchange vs. time are shown to collapse onto the theoretical exchange curve developed from the pore-water velocity profile.
Year: 1999