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<br />these zones, as sediment is removed and transported by the debris flow to
<br />lower gradient segments of the channel. In contrast, the response of the
<br />deposition zone to the debris-flow event is aggradation as sediment is
<br />deposited by the debris flow. This aggradation, however. is Iollowed by
<br />degradation, when the debris-flow deposits were entrenched and scoured
<br />by hyperconcentrated flow or flood streamflow immediately after
<br />deposition. Degradation of the deposits probably continues through time as
<br />lateral and vertical erosion by fluvial processes removes sediment from the
<br />deposition zone.
<br />The geomorphic eIlect of the debris-flow event extends beyond the
<br />debris flow deposition zone as sediment eroded from the debris-flow
<br />impacted channel is incorporated into floodwaters immediately downstream
<br />of the deposition zone. The sediment distribution in the scour zones of
<br />Austin Run and Gravel Lick Run show that the highest volumes of erosion
<br />in this zone are directly upstream from the highest volumes of deposition
<br />(Fig. 1). This indicates there is minimal transport of the sediment eroded by
<br />floodwaters in the scour zone.
<br />RESEARCH NEEDS
<br />Quantifying the distribution of sediment in a debris.flow impacted
<br />channel provides a better understanding of the geomorphic role of debris
<br />flows on channel morphology. However, little is known of the response of
<br />channels after the debris.flow event. For example, how does the channel
<br />system respond, over time, in areas impacted by debris-flow erosion and
<br />depOSition. This information is critical to understanding the long-term
<br />effectiveness of debris flows on channel morphology.
<br />REFERENCES CITED
<br />Benda, L., 1990, The influence of debris flows on channels and valley
<br />floors in the Oregon Coast Range. U.S.A.: Earth Surface Processes
<br />and Landforms, v, 15, p, 457-466.
<br />Campbell, R.H.. 1975, Soil Slips, Debris Flows, and Rainstorms in the Santa
<br />Monica Mountains and Vicinity, Southern California: U.S.G.S.
<br />Professional Paper B51, 51 p.
<br />Cenderelli, D.A.. and Kite, J,S., 1993, Sediment production, transport, and
<br />deposition in four debris-flow channels on North Fork Mountain,
<br />eastern West Virginia: 6.S.A., Abstracts with Programs. v. 25.
<br />Hack, J.T., and Goodlett, J,C" 1960, Geomorphology and Forest Ecology
<br />of a Mountain Region in the Central Appalachians: U.S.G.S.
<br />Professional Paper 347, 66 p,
<br />Pierson. T .C.. 1980. Erosion and deposition by debris flows at Mount St.
<br />Thomas, North Canterbury, New Zealand: Earth Surface Processes
<br />and Landforms, v. 5, p. 227-247.
<br />Williams. G.P. and Guy, H.P., 1973. Erosional and Depositional Aspects of
<br />Hurricane Camille in Virginia. 1969: U.S.G.S. Professional Paper
<br />804, 80 p.
<br />Wohl, E,E.. and Pearthree, P,P., , 991, Debris flows as geomorphic
<br />agents in the Huachuca Mountains of southeastern Arizona:
<br />Geomorphology, v, 4, p. 273-292.
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<br />Size Olaracteristics of Debris Flow Deposition
<br />
<br />Zhao Huilin and Olen Yingyanl
<br />
<br />Abstract
<br />
<br />The size distribution of debris flow deposition is extremely wide which
<br />may contain nearly all particles from c1~y and colloid to boulder: Particle size
<br />and composition bave very importan! mflueoce on tbe fo~atlon,. transport
<br />and deposition of debris flow, EspeCIally, the clay and coll~ld particles hav,e
<br />direct relation to physical properties and structure of debns flow, For 1~1S
<br />reason, size analysis is a kind of important means and metbod of studymg
<br />debris flow deposition,
<br />
<br />In this paper, on the foundation of lots of experiments on the size
<br />romposilion of debris flow deposition, till and river sedimental)' samples,
<br />which were taken from Sichuan province, Yunnan province, and Gansu
<br />province in China, are compared and discussed. Their size parameters, such
<br />
<br />as: size mean value i.., standard deviation U l/I' skewness Sk and kurtosis K,
<br />and the dispersive point graphs of the size parameters are presented.
<br />
<br />The research results above show that the size characteristics of debris
<br />flow deposition are different from till and river deposition, since they have
<br />differenltransport way and flow properties.
<br />
<br />I( 'hengdu Institute of Mountain Disasters and Environment, Chinese Academy of Sciences and
<br />Minislry of Water Conservancy, Chengdu, Sichuan 610041, P.R. China.
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