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Bed stability in unconfined gravel bed mountain streams: With implications for salmon spawning viability in future climates
Author(s) -
McKean Jim,
Tonina Daniele
Publication year - 2013
Publication title -
journal of geophysical research: earth surface
Language(s) - English
Resource type - Journals
eISSN - 2169-9011
pISSN - 2169-9003
DOI - 10.1002/jgrf.20092
Subject(s) - overbank , oncorhynchus , tributary , hydrology (agriculture) , streams , canyon , chinook wind , floodplain , geology , bed load , environmental science , shear stress , deposition (geology) , sediment transport , geomorphology , fishery , sediment , geotechnical engineering , geography , fluvial , fish <actinopterygii> , computer network , materials science , cartography , structural basin , computer science , composite material , biology
Incubating eggs of autumn‐spawning Chinook salmon ( Oncorhynchus tshawytscha ) could be at risk of midwinter high flows and substrate scour in a changing climate. A high‐spatial‐resolution multidimensional hydrodynamics model was used to assess the degree of scour risk in low‐gradient unconfined gravel bed channels that are the favored environment for autumn‐spawning salmon in mountain watersheds such as the Middle Fork Salmon River (MFSR), Idaho. In one of the most important MFSR spawning tributaries, near‐bed shear stresses were relatively low at all discharges from base flows to 300% of bankfull. The highest stresses were found only in small areas of the central flow core and not at spawning sites. Median shear stresses did not increase in overbank flow conditions because poor channel confinement released the excess water into adjacent floodplains. Channel and floodplain topography, rather than discharge, control the maximum near‐bed shear stresses. Over the modeled range of discharges, ~2% of the total surface area of the main stem channel bed was predicted to be mobile. Even in known spawning areas, where shear stresses are higher, ≤20% of the spawning surface area was mobile during overbank flows with a 2 year recurrence interval. Field measurements of little gravel transport during flows that were 93% of bankfull support the numerical model predictions. Regardless of some uncertainty in future climates in these watersheds, there appears to be relatively limited risk of extensive scour at salmon spawning sites in any likely hydrologic regimes.