ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

Large amount of information about morphology and dynamics
of sandy beaches in the coastal zone of the non-tidal
Black Sea mainly on the example of Ukrainian shores has
been accumulated and processed. Two main types of beaches
were considered: with lean-to (foreshore) profile and
two-sloping (gable) profile (with foreshore and backshore
sides). Beaches containing in themselves from 10 to 40
m'z'm of sand prevail. Numerical correlations between linear
and volumetric parameters of the beaches were obtained.
It was found out that the parameters are relatively stable
during long-term period. Under the impact of wave regime
during storms and some seasons beach undergo
short-term deformation values fluctuate around certain
average value are different in correspondence with concrete
local conditions. This conclusion was elaborated for
coast-protective constructions of different types, which gives
opportunity to optimize planning, management and
operation of coast-protective structures.
In the paper in succession are given: conditions of development
and definition of sandy beaches, morphodynamical
types and development in duration of time, the results
of the study of correlation between same parameters of natural
beaches sizes. Then we consider the problem of creating
and dynamics of artificial beaches from the position of
correlation of beach dimensions and wave energy regulation.
Such approach has practical importance for projection,
management and operation of the beaches as a means
of abrasive and erosive shore protection against wave destruction.
In natural conditions of the Northern Black Sea
coastal zone sandy beaches are subjected to the action of
storm waves from 0.5 to 5.1 m high. The most effective waves
higher than 1.25 m, act during 470-850 hours a year in
the average for a long-term period (5.4-9.7 % a year) in different
sectors of the coastal zone. The average reoccurence
of wave height more than 3 m is 0.04-0.07 % (or 35-62
hours) a year. The strongest sandy beach deformations
take place during the action of the waves higher than 1.25
m. As a rule stormy waves are steep, usually 0.03-0.08. The
main conclusions are:
- As a result of long-term instrumental measurements
sandy beaches in the coastal zone of the non-tidal Black
Sea were studied.
- The amount of drifts contained within the beach is its
universal dimension, numerical values being different
within various alongshores lithodynamical cells within a
coastal zone.
- The parameters of sandy beach are closely interconnected
with rather high coefficient of correlation, which indicates
of close connection with the full complex of forming
factors and processes.
- Relative stability, constancy of long-term dimensions of
sandy beaches preserve against the background of essential
short-term variations around the average value within strictly
definite limits.
- Regularities of natural development of beaches must be
used in the processes of planning, management and exploitation
of shore-protective structures. In this connection three
main scenarioes taking into account the correlation of
dimensions (volume) of artificially created beaches, and
ammount of wave energy acting on beaches: artificial increase
of protecting beach sizes by means of artificial filling
with preservation of non-changed wave energy flow;
artificial reduction of wave energy amount with preservation
of previous natural supply of drifts on protecting beach;
artificial reduction of wave energy amount and increase
of protecting beach dimensions by artificial filling of drifts.
- Numerical values of lithodynamical cubic content and limits
of short-term deformations of beach parameters are
different in various alongshore lithodynamical cells and sites
of the coastal zone.
REMO MASSARI & P.M. ATKINSON
Modelling susceptibility to landslide:
an approach based on individual landslide type
Department of Geography, University of Southampton,
Highfield, Southampton SOI7 IB], U.K.
Landslide hazard mapping amounts to map the probability
of landsliding within a given region (that is, where landslides
might occur in the future) in a given time scale (Hansen,
1984). This may be achieved using both direct and indirect
approaches. A landslide map may be used to some
extent as a landslide hazard map because slopes that have
already failed are likely to be composed of weaker material
that may be subject to further movements. However, a
landslide map fails to assess the landslide hazard for slopes
that have not yet failed, and generally overestimates the hazard
for areas that have already failed. Therefore, it is generally
necessary to attempt to map the landslide hazard.
A landslide hazard map should include an indication of the
time scale within which a particular landslide is likely to
occur. In practice, data on the temporal dimension of the
landslide hazard are difficult to obtain, since landslide triggering
is usually due to external causes (rainfall or earthquakes).
For this reason landslide hazard maps are usually
simple landslide susceptibility maps (Carrara & alii, 1996).
When attempting to map landslide susceptibility, one never
has data on future landslides. The statistical model is
constructed between data on past landslides and a set of
selected independent variables. As a consequence, the estimated
susceptibility is likely to be similar to a landslide
map. The assumption is that, for those slopes that have not
already failed, the relative differences in the estimated values
may point to relative differences in susceptibility to
landsliding.
The selection and definition of independent variables is a
key point in modelling landslide susceptibility. For example,
old landslide areas are sometimes reforested partly as a
result of a slope stabilisation program. In a statistical model,
landslides will be positively correlated with reforestation.
However, reforestation is a post-landslide condition
and, clearly, does not imply an increase in susceptibility to
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