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Partial entrainment of gravel bars during floods
Author(s) -
Konrad Christopher P.,
Booth Derek B.,
Burges Stephen J.,
Montgomery David R.
Publication year - 2002
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 - 10.1029/2001wr000828
Subject(s) - entrainment (biomusicology) , flood myth , dimensionless quantity , hydrology (agriculture) , environmental science , geology , geotechnical engineering , mechanics , physics , rhythm , acoustics , philosophy , theology
Spatial patterns of bed material entrainment by floods were documented at seven gravel bars using arrays of metal washers (bed tags) placed in the streambed. The observed patterns were used to test a general stochastic model that bed material entrainment is a spatially independent, random process where the probability of entrainment is uniform over a gravel bar and a function of the peak dimensionless shear stress τ 0 * of the flood. The fraction of tags missing from a gravel bar during a flood, or partial entrainment, had an approximately normal distribution with respect to τ 0 * with a mean value (50% of the tags entrained) of 0.085 and standard deviation of 0.022 (root‐mean‐square error of 0.09). Variation in partial entrainment for a given τ 0 * demonstrated the effects of flow conditioning on bed strength, with lower values of partial entrainment after intermediate magnitude floods (0.065 < τ 0 *< 0.08) than after higher magnitude floods. Although the probability of bed material entrainment was approximately uniform over a gravel bar during individual floods and independent from flood to flood, regions of preferential stability and instability emerged at some bars over the course of a wet season. Deviations from spatially uniform and independent bed material entrainment were most pronounced for reaches with varied flow and in consecutive floods with small to intermediate magnitudes.