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Alluvial Morphodynamics of Low‐Slope Bedrock Reaches Transporting Nonuniform Bed Material
Author(s) -
Jafarinik S.,
Viparelli E.
Publication year - 2020
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2020wr027345
Subject(s) - bedrock , alluvium , geology , geomorphology , beach morphodynamics , sediment transport , sediment , trench , bedform , fluvial , hydrology (agriculture) , alluvion , geotechnical engineering , structural basin , chemistry , organic chemistry , layer (electronics)
Recent studies reveal that low‐slope bedrock reaches (bedrock surface slope milder than ~5 m/km) are more common than previously thought and can be found in engineered rivers and densely populated deltas. Here we present a novel formulation of alluvial morphodynamics of low‐slope bedrock rivers transporting nonuniform bed material that accounts for the nonuniformity of the sediment size and the presence of small scale bedforms such as dunes and can thus be of aid to solve management/restoration problems in low‐slope bedrock rivers. The formulation is implemented in a one‐dimensional morphodynamic model. Numerical results are compared with laboratory experiments on equilibrium bedrock reaches downstream of stable alluvial‐bedrock transitions. The differences between experimental and numerical results are comparable with those obtained in the alluvial case. Model applications simulate (1) bedrock reaches with a stable bedrock‐alluvial transitions, (2) an alluvial‐bedrock transition subject to sea level rise, and (3) steep bedrock reaches. Upstream of a stable bedrock‐alluvial transition the flow decelerates in the streamwise direction with the formation of a stable pattern of downstream coarsening of bed surface sediment. In response to sea level rise, alluvial‐bedrock transitions migrate downstream and bedrock‐alluvial transitions migrate upstream. Opposite migration directions are expected in the case of sea level fall. When applied to steep channels, the model predicts gradual alluviation, but it fails to reproduce runaway alluviation.