Hyporheic Flow in Coarse Gravel Beds: A Laboratory Investigation

Abstract:

Flows over permeable walls are ubiquitous in nature, with hyporheic flow playing a key role in subsurface-surface exchange, particulate dispersal and accumulation and the ecology of the top few pore spaces of a sediment bed. The study of flow dynamics in hyporheic flow is relevant to improve our understanding of the transport processes crucial for balanced ecosystems in a range of environments. In this paper, we report experimental measurements of mean velocities and turbulent fluctuations in the upper five pore spaces of an idealized gravel bed beneath a turbulent water flow. These experiments were conducted in the Hyporheic Flow Facility (HFF) at the University of Illinois. Systematic two-dimensional flow measurements were collected by an endoscopic Particle Image Velocimetry technique (EPIV), at five different pore locations with varying wall-normal distance from the interface. Several different surface flow conditions varying in Re and Froude have been investigated for all the pore space measurements. Herein, we report on the effect of the flow Reynolds number and Froude number on the flow structure within these five pore spaces, and examine the changing nature of mean flow and turbulence penetration with depth in the sediment bed.