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Hyporheic Exchange Under Undular Flows Over a Coarse Granular Bed
Author(s) -
Shih WuRong,
Wu FuChun
Publication year - 2020
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2020gl089114
Subject(s) - pressure gradient , flux (metallurgy) , hydrology (agriculture) , flow (mathematics) , environmental science , geology , channel (broadcasting) , hyporheic zone , front (military) , mechanics , geomorphology , materials science , physics , geotechnical engineering , oceanography , sediment , engineering , electrical engineering , metallurgy
Undular flows over riffles (standing waves with underlying open‐channel flows) facilitate a quality environmental setting for riverine habitats. Understanding their link with hyporheic exchange flow (HEF) is important from eco‐hydro‐geomorphic perspectives. We conduct refractive index‐matched scanning experiments to resolve the exchange between surface and subsurface flows across a coarse granular bed. We show that the HEF includes wave pumping (WP) and grain‐scale pumping (GP) components. Mechanistically, the dynamic pressure gradient best explains the HEF on both wave and grain scales. However, due to the underlying open‐channel flow, the result exhibits a phase lag compared to the theoretical WP, suggesting a necessary shift from the existing water surface‐based model to a pressure gradient‐based approach. Quantitatively, with the present experimental setting, the GP flux is 1 order of magnitude smaller than the WP flux. The relative significance of WP to GP is further increased at higher discharges, indicating potential utility of WP in habitat vitalization.