ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

The numerical model used in this study is based on a set of
deterministic equations of flow momentum, flow resistance,
sediment transport and conservation of sediment mass.
The model is solved with a set of specific boundary conditions
(discharge and sediment load at the upstream boundary
of the modelled reach) to obtain predictions of bed
elevation change through time. Channel width adjustment
is accounted for through analysis of specific mechanisms of
bank erosion, mass failure, and deposition and subsequent
entrainment of failed bank-material debris. The effects of
riparian vegetation in any discrete time step are accounted
for through static analyses of the impacts of specific vegetation
types and arrangements on (1) flow resistance, and
(2) geotechnical characteristics of the bank materials.
Dynamic interactions between riparian vegetation colonization
and growth on re-stabilizing bank surfaces are accounted
for through use of idealized, site-specific, vegetation
growth functions. Dendrochronology studies along disturbed
channels in Mississippi and West Tennessee have
been used to develop growth functions for various riparian
species. For all woody species combined, mean annual rates
of tree diameter and rooting-depth growth were found
to be about 1.0 em/yr. Vegetation parameters (height, diameter,
rooting depth) are varied through time according to
these empirically-derived growth functions. Riparian vegetation
is removed from unstable banklines after mass failure.
Vegetation re-growth on stabilizing bank surfaces which
failed in previous time steps is simulated using the idealized
growth functions. It is recognized that this is a highly
simplified representation of geomorphic and vegetative recovery
processes.
The effects of riparian vegetation on channel adjustment
processes were analyzed in a series of sensitivity analyses,
carefully calibrated to reflect the conditions encountered
in Goodwin Creek and the South Fork Forked Deer River.
To quantify the effects of different types of riparianvegetation
on channel adjustment in these streams, simulations
were conducted for cases when (1) riparian vegetation is
totally absent; (2) riparian vegetation consists of herbaceous
vegetation only, and; (3) riparian vegetation consists
of woody vegetation only. In the case of woody vegetation,
additional simulations were conducted to evaluate the influence
of different species on channel dynamics. This was
done by using empirically-derived growth functions specific
to each of the species analyzed, in conjunction with the
use of rooting depth and root tensile strength values representative
of,and specific to, those species. Simulations were
conducted for the following species (1) river birch (Betula
nigra); «2) black willow (Salix nigra); (3) sycamore
(Platanus occidentalis), and; (4) alder (Alnus serrulatai.
These are common pioneer species along disturbed channels
of Mississippi and Tennessee. Results are presented
for both study reaches in terms of comparisons between simulated
changes, through time, in channel width, thalweg
'elevation, channel gradient, and cross-section shape corresponding
to each of the specific riparian vegetation types
simulated.
SUNIL KUMAR DE
Assessment of soil-loss in the Balasan of the
Darjeeling Himalaya
Department of Geography, Calcutta University,
35, Ballylgunge Circular rd., Calcutta, 700019, India
The Balasan Basin situated in the Darjeeling Himalaya
constitutes a fragile and unique ecological system. This basin
is frequently devasted by environmental catastrophies,
Among such events landslide is perhaps the most rampant
environmental hazard threatening the Town of Kalimpong
adjoining the basin.
In order to have an in sight into the probable cause of such
increased vulnerability, the author in this paper has tried
to trace the course of events by drawing together the nature
and amount of soils loss calculated on the basis of
Fao/Vnep, Usle and Usda methods.
Of the five vulnerable zones, the zone falling in between
600 to 1,800 m is consideredto be the most unsafe due to
high rainfall, fragile geological structure, deforestation and
unscientific use of the land by ever growing population.
Immediate measures should therefore be taken to stop such
menace and restore the natural ecological balance of the
basin under consideration.
DIRK H. DE BOER
Using fractal dimensions to quantify changes in the
morphology of fluvial suspended sediment particles
during baseflow conditions
Department of Geography, University of Saskatchewan,
9 Campus Drive, Saskatoon, Saskatchewan, S7N 5A5, Canada
The morphology of suspended sediment particles reflects
the origin of the suspended load and any modifying processes
which may have occurred during transport and storage
in the aquatic system. The objective of this study was
to evaluate the use of four fractal dimensions to quantify
visually observed changes in the morphology of fluvial suspended
sediment particles during baseflow conditions.
Samples were collected during summer low flow in a small
stream on the Canadian prairies. Particle morphology data
were obtained with a transmitted light microscope, aCed
camera, and an image analysis system.
The morphology of the particle population was characterized
using four fractal dimensions (D, Db D 1 , and D 2 ) . D
was derived from the area-perimeter relationship and
showed an increase from 1.26 ± 0.02 on June 30, to 1.34 ±
0.02 on July 4, to 1.42 ± 0.01 on July 7. Visually, the increase
in D represented the formation of large particles
with intricate shapes and increased perimeters. D, was de-
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