Experimental study of bedform-driven hyporheic exchange

In order to test the bedform impacts on the hyporheic exchange behavior, the tracer NaCl is used to test the hyporheic exchanges under four groups of bedforms in a water-circling flume. Based on the diffusion theory, the impacts of hydrodynamics of water column and permeability of underlying sediments on the hyporheic flow are analyzed. Results show that the hyporheic exchanges can occur on a flat bedform. The exchange rate can be intensified under a more uneven bedform and a higher Reynolds number. Compared to the factor of water depth, the hyporheic exchange rate is much more sensitive to the velocity of the surface water. In addition, the effective diffusion coefficient is proportional to the square of characteristic grain diameter, and has a linear relationship with the streambed hydraulic conductivity. Also, the exchange depth in the flume is found to be proportional to the Re^1/2.