ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

with flow through the soil, we recognize five major flow
stages of increasing discharge. In the first stage (detention)
flood plain hollows are disconnected; in the second (Darcian)
the connections are built up and flow occurs between
cells. In the third stage (macropore) connected flow through
the reach occurs, with one or several channels having
faster flow than with poorly connected flow and at the
fourth stage, flow is sufficient to occupy the entire channel
but is entirely within the boundary layer. Finally the channel
is filled beyond the boundary layer and can conform to
the usual assumptions of unsteady flow in perennial channels.
Some or all of these conditions may occur in any flow
and the hydraulic conditions are different at each flow stage.
Effort is concentrated at this stage in defining the behavior
of flows in the first three stages.
Our approach comprises supplying water at the upper
boundary of the plot as a hydrograph (from a basin model)
that is distributed by channel cross section depths (after
Baird, Watts & Thornes, 1992), with the flows generating
random walks through the topography. From this the distribution
of mean first passage times, boundary impacts,
network characteristics and similar flow response variables
are derived from theoretical and digital simulation models
and validated against scale model hardware simulations.
The discrete random walks are developed first on a finite
difference mesh, using local channel slope as the direction
criterion and the path frequency per cell as a method of
generating flow depths and velocities and therefore is somewhat
similar to hillslope flow algorithms and to Murray
& Paola, 1994. The results comprise a set of output hydrographs
from both hypothetical and actual channel reaches,
with characteristic bed configurations, and for the actual
channels we compare the results with finite element modelling
of the flow equations. In a second formulation we
consider the process as a continuous Markov process with
varying time steps, though this work is still in its infancy
and will be reported on at the meeting.
DOUGLAS T. SHERMAN & EUGENE J. FARRELL
Shear velocity - saltation layer interactions
Department of Geography, University of Southern California,
University Park, Los Angeles, California 90089, U.S.A.
For equilibrium saltation in aeolian systems, the vertical distribution
of mass flux should be dependent upon shear
velocity, and sediment size. It is widely recognized that
mass flux in the saltation layer is distributed in a semi-logarithmic
manner, with most of the sediment transport occurring
within a relatively short distance above the surface.
Further, the presence of saltating grains modifies the distribution
of wind speeds above the surface, resulting in an
apparently increased roughness length.
Owen (1964) was the first to express the implicit relationship
between the shear stress and surface roughness pa-
rameter for a saltating system. He developed an expression
relating mean saltation height, h, to shear velocity:
h = 0.82 ui'//g, where g is the gravitational constant. During
saltation Owen hypothesized that the saltation layer
and boundary roughness are intrinsically related whereby
«the saltation layer behaves, so far as the flow outside it is
concerned, as an aerodynamic roughness whose height is
proportional to the thickness of the layer» (Owen 1964, p.
226). His analysis was dynamically similar to that of Charnock
(1955) in his examination of fully developed turbulent
air flows over water. Charnock suggested that
zo=aui'//g, where Zo is the surface roughness length, and a
is the Charnock constant. For aeolian saltation Sherman
(1992) modified Charnock's equation and described the
equilibrium relationship between shear velocity and an apparent
roughness length.
This study builds from these investigations. Specifically,
we demonstrate that field experiments suggest that mean
saltation height is relatively insensitive to changes in shear
velocity, at least over ranges of transport conditions typical
to beaches. Most sand transport occurs below about 0.05
m above the surface. We also examine 10 data sets (both
laboratory and field based) in the context of the modified
Charnock equation, and demonstrate that the empirical
constant is substantially and significantly larger for field
data than for the laboratory data. This suggests that basic
physical relationships may not be readily transferable from
the lab to the field.
HIROSHI SHIMAZU
Catastrophic debris transport along
the japanese mountain river
Department of Geography, Rissho University, Osaki,
Shinagawa, 141 Tokyo, Japan
The Upper Tedori river basin, central Japan experienced
catastrophic debris transport in July 11, 1934. This event
were triggered by a rainstorm with a cumulative two days
rainfall of approximately 466 mm. Since this event there
have been many huge blocks on the river bed. The largest
one is more than 10 meters in b-axis. Debris flows, which
consist of huge blocks and which do not triggered by a large
landslide, generally deposit along the river with about
8 % in channel slope. But in this event the blocks were
transported more than several kilometers along the river
whose channel slope is as small as 3 %. To examine the origin
of the blocks and the cause of the debris transport the
author investigates morphology and sediments in the upper
Tedori river basin.
The upper Tedori basin has an area of about 140 square
kilometers and an elevation range of 500 to 2702 meters.
This basin is underlain by sedimentary rocks and lava of
the Hakusan volcano, and is largely covered with the alpine
and subalpine vegetation and the forest of Fagus. Along
this river and its tributaries several levels of terraces are di-
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