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Downstream Fining and Sorting of Gravel Clasts in the Braided Rivers of mid‐Canterbury, New Zealand
Author(s) -
Browne Greg
Publication year - 2004
Publication title -
new zealand geographer
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.335
H-Index - 25
eISSN - 1745-7939
pISSN - 0028-8144
DOI - 10.1111/j.1745-7939.2004.tb01708.x
Subject(s) - clastic rock , sorting , geology , entrainment (biomusicology) , geomorphology , sediment , sediment transport , three gorges , graded bedding , bedform , fluvial , river mouth , hydrology (agriculture) , bed load , geotechnical engineering , programming language , aesthetics , computer science , rhythm , structural basin , philosophy
Gravel clast size dimensions have been determined in the Rakaia, Ashburton, and Rangitata rivers by measuring 100 clasts at representative sample locations along each river. In all rivers, gravel size decreases and sorting improves downstream for mean, D 50 , and D 90 fractions of the bed material. Clast size entering the sea is similar in all rivers (30–40 mm b‐axis dimension), despite large variations in transport distance, input size of clasts at their gorges, and discharge. The greatest size reduction occurs in the Rangitata River which has the shortest transport distance and steepest gradient. Rates of downstream clast size reduction are greater than would be assumed from Sternberg's Law, suggesting that additional factors, other than physical abrasion, such as sorting and selective entrainment operate.