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Title: Unstable turbulent channel flow response to spanwise-heterogeneous heat fluxes: Prandtl’s secondary flow of the third kind
Award ID(s):
1649067 1712538
Author(s) / Creator(s):
; ;
Date Published:
Journal Name:
Journal of fluid mechanics
Medium: X
Sponsoring Org:
National Science Foundation
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  1. Abstract

    Intermittent streams currently constitute >50% of the global river network, and the number of intermittent streams is expected to increase due to changes in land use and climate. Surface flows are known to expand and contract within the headwater channel network due to changes in the water table driven by climate, often changing seasonally. However, the underlying causes of disconnections and reconnections throughout the stream network remain poorly understood and may reflect subsurface flow capacity. We assess how 3D subsurface flowpaths control local surface flows at Gibson Jack Creek in the Rocky Mountains, Idaho, USA. Water table dynamics, hydraulic gradients, and hyporheic exchange were monitored along a 200‐m section of the stream throughout the seasonal recession in WY2018. Shallow lateral hillslope‐riparian‐stream connectivity was more frequent in transects spanning perennially flowing stream reaches than intermittent reaches. During low‐flow periods, larger losing vertical hydraulic gradients were observed in paired piezometers in intermittent reaches than in adjacent perennial reaches. Contrary to dominant conceptual models, longitudinal measurements of hydrologic exchange in both intermittent and perennial reaches were seasonally variable except for one perennial reach that showed consistent significant gains. Observed drying dynamics, as well as subsurface pathways, were highly variable even over short distances (30 m). Flow probability and subsurface flow capacity at upstream locations can be assessed with an outlet hydrograph and upstream flow measurements. Accurate characterization of subsurface storage, discharge, and connection is critical to understanding the drivers of drying cycles in intermittent streams and their likely responses to future change.

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