ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

tion analyse of the periglacial landforms in a representative
part of the South Shetland Islands.
Finally, 26 types of periglacial landforms have been inventoried:
Slope landforms: debris slopes, talus and cones,
protalus ramparts, rock glaciers, stone stripes (coarse and
fine), terraced debris lobes, ploughing blocks, gelifluction
lobes, debris lobes; landforms associated with permafrost:
patterned ground (stone rings, poligonal ground), fussion
hollows, stone fields, cryoplanation terraces, gelifluction
sheets; nivation landforms: debris flows, mudflows, nivation
niches, nivation pavements, flat-floored valleys, assymetrical
valleys, sandur; weathering of the bedrock: laminated
cracking, tors.
Most of the landforms are active at present, specially those
above 10 m a.s.l. However, an attenuation of the periglacial
activity in relation to previous periods has been pointed
out, being signalated by the presence of inactive
landforms colonized by lychens, that denote recent environmental
changes. At the present time, crionival processes
and in second place those associated to the active layer
are dominant. The permafrost has been studied by means
of surface temperature measurements (Deception Island),
seismic and geoelectric sounding (Caleta Espanola, Hurd
Peninsula), shallow coring (Deception Island and Byers
Peninsula) and, in general, by landforms analyse and study
of periglacial morphosequences. Depths of the active layer
have been reconnaised at 10-96 em below the surface,
always at altitudes of more than 10 m a.s.l. except in Deception
Island.
The distribution of the periglacial landforms in altitude
shows that 8% of these landforms are located at altitudes
between 0 and 20 m a.s.l., being most of them above 10 m
and associated to slope processes. The greatest presence of
periglacial landforms is between 20 and 50 m, being stone
fields and patterned ground the most common. Same types
of landforms are also present between 50 and 100 m, but
in less quantity. Above 100m slope landforms are again dominant.
JOANNA 1. SHANAHAN, D.E. WALLING & T.A. QUINE
Sediment delivery in a small, agricultural catchment,
Devon, UK
Department of Geography, University of Exeter,
Rennes Drive, Exeter, EX4 4RJ, UK
Agricultural non-point pollution in the UK has increased
significantly in recent years owing to the intensification of
farming practices. Accelerated soil erosion and soil degradation
lead to a loss of productivity on-farm and to an increase
in suspended sediment transported by rivers. Sediment
acts as both a pollutant and as a vector for nutrient
and chemical contaminants. Spatial and temporal discontinuities
exist between on-site erosion and downstream sedi-
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ment yield. An improved understanding of the complex
nature of sediment delivery is therefore required to design
effective pollution control strategies. The findings of an intensive'
spatially-distributed study of a small, agricultural
catchment, Devon, UK, are presented. Several techniques
were employed to elucidate the sediment delivery dynamics
of the basin at a range of spatial and temporal scales.
The relative contribution of suspended sediment sources
to sediment yield was established using the fingerprinting
technique. Medium-term rates of soil erosion and deposition
were estimated using 137CS. Various measurements of
contemporary erosion, transport and deposition were
taken over a two-year period. Linear elements in the landscape
including tractor wheelings, rills and ditches were
found to be important zones for the erosion and conveyance
of sediment. Grass and woodland buffer areas showed
significant levels of sediment storage. Sediment budgets
were developed on both the catchment and subcatchment
scale. The paper highlights the importance of an integrated,
basin-scale approach to the study of sediment delivery
and its controls.
TULlE SHANNON & JOHN B. THORNES
A probabilistic approach to modelling of ephemeral
channel flow and sediment transport
King's College London, Strand, London WC2R 2LS, U.K.
In ephemeral channels the flow is intermittent and asynchronous,
the channel bed and boundaries are highly mobile
and very irregular and waves of sediment occur in the
channel. Transmission losses to the bed and the presence
of both vegetation and anthropogenic features, such as excavation
hollows and check dams, mean that conventional
routing techniques are inapplicable either for technical or
conceptual reasons, except when the channel is behaving
more like a perennial river i.e. in extremely rare events. On
these occasions the strongly unsteady nature of the flow in
any case precludes the use of many standard methods. Under
these circumstances the adoption of a probabilistic
methodology seems especially appropriate. Todorovic &
Woolhiser (1962) already attempted to provide a general
sediment transport model for such conditions that consisted
of obtaining a multi-dimensional aggregate probabilistic
distribution of flow events upon which the sediment
transport was piggy-backed. Others have attempted to
build a sediment rating onto a probabilistic flow routing,
while yet other (Smith, 1972) attempted to develop an
analytical solution to the forward propagation of the wave
front across a dry bed using the dam-burst modelling approach.
In this paper we describe the conceptual basis, theoretical,
laboratory and field investigations and preliminary results
of investigations to model these phenomena. By analogy