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Displacement and transport of marked pebbles, cobbles and boulders during floods in a steep mountain stream
Author(s) -
Lenzi Mario Aristide
Publication year - 2004
Publication title -
hydrological processes
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.222
H-Index - 161
eISSN - 1099-1085
pISSN - 0885-6087
DOI - 10.1002/hyp.1456
Subject(s) - bed load , hydrology (agriculture) , hyperconcentrated flow , geology , snowmelt , flood myth , sediment transport , stream power , cobble , winnowing , geomorphology , drainage basin , streams , sediment , snow , geotechnical engineering , geography , cartography , archaeology , habitat , biology , ecology , computer network , computer science
In a small experimental catchment of the Dolomites (Rio Cordon, 5 km 2 ) field observations have been carried out on the movement of various sized bed material particles. Displacement length of 860 marked pebbles, cobbles and boulders (0·032 < D < 0·512 m) has been measured along the river bed during individual snowmelt and flood events in the periods 1993–1994 and 1996–1998. Floods were grouped into two categories. The first includes ‘ordinary’ events, which are characterized by peak discharges with a return period of 1–5 years and by an hourly bedload rate not exceeding 20 m 3 h −1 . The second refers to ‘exceptional’ events with a return period of 50–60 years. A flood of this latter type occurred on 14 September 1994, with a peak discharge of 10·4 m 3 s −1 and average hourly bedload rate of 324 m 3 h −1 . The variation according to grain size of total displacement length L i depends on the degree of mobilization of the individual fractions of the bed surface: L i is independent of D i for smaller, fully mobile grain sizes and decreases rapidly with D i for larger fractions in a state of partial transport. Sustained selective transport without a supply of sediment from upstream leads to the development of a stable coarse armoured surface through progressive winnowing of finer material from the bed surface. With supply unlimited conditions for transport, both the occurrence of extreme events and the duration of a sequences of ‘ordinary’ floods play an important role in the degree of mobilization of the individual fractions of the bed. Copyright © 2004 John Wiley & Sons, Ltd.