The aim of this thesis is to investigate the effect underflow and diffusion have on hyporheic exchange. Hyporheic exchange has in many studies been shown to be mainly driven by the effect of Pumping, which describes the flow into and out of the sediment by the occurrence of pressure gradients. A theoretical model of Pumping has therefore in this study been used to calculate a velocity field in the hyporheic zone. The parameter for the underflow was then varied within a realistic range and combined with different strengths of the diffusion coefficient. Different set ups of the Pumping-underflow-diffusion composition were then simulated by a numerical random walk procedure and compared to each other. The result of the analysis was that diffusion and underflow both have a noticeable impact on the residence time behaviour of particles within the bed. Especially their combination resulted in greatly varying spatial and temporal distributions of the solute.     «

The aim of this thesis is to investigate the effect underflow and diffusion have on hyporheic exchange. Hyporheic exchange has in many studies been shown to be mainly driven by the effect of Pumping, which describes the flow into and out of the sediment by the occurrence of pressure gradients. A theoretical model of Pumping has therefore in this study been used to calculate a velocity field in the hyporheic zone. The parameter for the underflow was then varied within a realistic range and combin...     »