The effects of hillslope and fluvial processes on particle size of the stream bed at the watershed, reach and within-reach scales in a fifth-order mountain stream

approved: (Julia Allen Jones) This study addressed the effects of hilislope and fiuvial processes on spatial patterns of stream bed particle size at the watershed, reach and within-reach scales. The study was conducted in Lookout Creek watershed, a fifth-order, 64 km2 basin in the Western Cascades mountains of Oregon. Stream bed particle size was measured at 25 sites on firstthrough fifth-order streams. Boulder density was measured from the headwaters of the mainstem of Lookout Creek to its mouth, approximately 16 kilometers of stream length. In Lookout Creek watershed, spatial patterns of particle size result from a hierarchy of hydraulic and hilislope controls. At the watershed scale, hydraulic controls explain around 50% of the variation in d50 and d84. Particle size is related to watershed-scale trends in stream power and stream competence. At the reach scale, debris flows and landslides leave a patchy signature on stream bed particle size. Patches of both high and low boulder density are associated with landslides. A peak in density is associated with a February 1996 debris flow. Hydraulic controls are less evident at this scale, although the degree of reach constraint may affect particle size in fourthand fifth-order Lookout Creek. At the within-reach scale, hydraulic controls are responsible for around 20% of the observed particle size variation. The effects of the largest flood on record at Lookout Creek were documented at 7 sites that had been sampled before the flood. At the watershed scale, a fining in particle size was observed; this is consistent with the hypothesis that Lookout Creek has an armor layer which the flood disturbed. At the within-reach scale, changes in particle size appeared stochastic, and provided little information about the role of hydraulic controls at that scale. The Effects of IELillslope and Fluvial Processes on Particle Size of the Stream Bed at the Watershed, Reach and Within-Reach Scales in a Fifth-Order Mountain Stream

[1]  F. Swanson,et al.  Morphology and processes of valley floors in mountain streams , 2013 .

[2]  D. Dunkerley.  STONE COVER ON DESERT HILLSLOPES: EXTENT OF BIAS IN DIAMETERS ESTIMATED FROM GRID SAMPLES AND PROCEDURES FOR BIAS CORRECTION , 1996 .

[3]  Chih Ted Yang,et al.  Sediment transport : theory and practice / Chih Ted Yang , 1995 .

[4]  W. Marcus,et al.  Pebble Counts and The Role of User‐Dependent Bias in Documenting Sediment Size Distributions , 1995 .

[5]  C. Paola,et al.  Grain Size Patchiness as a Cause of Selective Deposition and Downstream Fining , 1995 .

[6]  J. Pizzuto.  Downstream Fining in a Network of Gravel‐Bedded Rivers , 1995 .

[7]  R. Ferguson,et al.  Numerical simulation of downstream fining by selective transport in gravel bed rivers: Model development and illustration , 1994 .

[8]  B. C. Wemple.  Hydrologic integration of forest roads with stream networks in two basins, western Cascades, Oregon , 1994 .

[9]  David Jon Furbish,et al.  Flow structure in a bouldery mountain stream with complex bed topography , 1993 .

[10]  Panayiotis Diplas,et al.  Surface Sampling in Gravel Streams , 1993 .

[11]  F. Swanson,et al.  Effects of coarse woody debris on morphology and sediment storage of a mountain stream system in western Oregon , 1993 .

[12]  P. Wilcock,et al.  Downstream Fining by Selective Deposition in a Laboratory Flume , 1992, Science.

[13]  E. Wohl.  Bedrock benches and boulder bars: Floods in the Burdekin Gorge of Australia , 1992 .

[14]  R. Ferguson,et al.  Slope-induced changes in channel character along a gravel-bed stream: the Allt Dubhaig, Scotland , 1991 .

[15]  L. Benda.  The influence of debris flows on channels and valley floors in the Oregon Coast Range, U.S.A. , 1990 .

[16]  F. Swanson,et al.  Pattern and origin of stepped-bed morphology in high-gradient streams, Western Cascades, Oregon , 1990 .

[17]  M. Dawson.  Sediment size variation in a braided reach of the Sunwapta River , 1988 .

[18]  Lyle W. Zevenbergen,et al.  Estimating Mean Velocity in Mountain Rivers , 1985 .

[19]  Richard D. Hey,et al.  Accuracy of Surface Samples from Gravel Bed Material , 1983 .

[20]  J. Whittaker,et al.  Origin of step-pool systems in mountain streams , 1982 .

[21]  R. D. Harr,et al.  Some characteristics and consequences of snowmelt during rainfall in western Oregon , 1981 .

[22]  M. Church,et al.  On the statistics of grain size variation along a gravel river , 1978 .

[23]  M. Gordon Wolman,et al.  Fluvial Processes in Geomorphology , 1965 .

[24]  M. Wolman.  A method of sampling coarse river‐bed material , 1954 .

[25]  M. Church,et al.  Bed material texture in low order streams on the Queen Charlotte Islands, British Columbia , 1996 .

[26]  T. Lisle.  Overview: Channel morphology and sediment transport in steepland streams , 1987 .

[27]  L. Benda,et al.  Sediment routing by debris flow , 1987 .

[28]  E. Keller,et al.  Relationships between channel morphology, unit stream power, and sediment routing and storage in a steep, beddrock controlled channel , 1987 .

[29]  A. Knighton.  Longitudinal changes in the size and shape of stream bed material: Evidence of variable transport conditions , 1982 .

[30]  W. Dietrich,et al.  Sediment budget for a small catchment in mountainous terrain , 1978 .

[31]  H. J. Mcpherson.  DOWNSTREAM CHANGES IN SEDIMENT CHARACTER IN A HIGH ENERGY MOUNTAIN STREAM CHANNEL , 1971 .

[32]  L. Brush.  Drainage basins, channels, and flow characteristics of selected streams in central Pennsylvania , 1961 .