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Pore-resolved direct numerical simulations (DNS) are performed to investigatethe interactions between streamflow turbulence and groundwater flow through arandomly packed porous sediment bed for three permeability Reynolds numbers,$Re_K$, of 2.56, 5.17, and 8.94, representative of natural stream or riversystems. Time-space averaging is used to quantify the Reynolds stress,form-induced stress, mean flow and shear penetration depths, and mixing lengthat the sediment-water interface (SWI). The mean flow and shear penetrationdepths increase with $Re_K$ and are found to be nonlinear functions ofnon-dimensional permeability. The peaks and significant values of the Reynoldsstresses, form-induced stresses, and pressure variations are shown to occur inthe top layer of the bed, which is also confirmed by conducting simulations ofjust the top layer as roughness elements over an impermeable wall. Theprobability distribution functions (PDFs) of normalized local bed stress arefound to collapse for all Reynolds numbers and their root mean-squaredfluctuations are assumed to follow logarithmic correlations. The fluctuationsin local bed stress and resultant drag and lift forces on sediment grains aremainly a result of the top layer, their PDFs are symmetric with heavy tails,and can be well represented by a non-Gaussian model fit. The bed stressstatistics and the pressure data at the SWI can potentially be used inproviding better boundary conditions in modeling of incipient motion andreach-scale transport in the hyporheic zone.

Pore-resolved investigation of turbulent open channel flow over a randomly packed permeable sediment bed