ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

en alternance d'un litho-facies impermeable, des grandes
surfaces arables sont affectees par erosion areolaire et torentielle
et par des glissements de terrain. Ainsi, de la surface
arable totale de 1.574.098 ha, 916.757 ha sont affectees
par l' erosion areolaire et torentielle et 62.000 ha par
des glissements de terrain en delferents stages d' evolution.
ALEXADRE o. BRINKEN
Geomorphology of seacosts and global changing
of climate
Russian Geographic Society
Grivtsova 10, St.-Petersburg, 190000, Russia
Widespread opinion about increasing of greenhouse-effect
because of intensification of human activity should cause
higher water level of the ocean. This is the modern point
of view.
But observations carried out during the last ten years on
many seacosts - Peruvian coast of the Pacific ocean, Hindustanian
coast of the Arabian sea, Coromandel coast of
the Indian ocean, Dutch coast of the North sea, Finnish
and Russian coast of the Baltic sea, Adzharian coast of the
Black sea and some others - don't prove such a conclusion.
They could prove long stability of a state or clearly show a
recession of a seacost (Madras fortress is divided from the
sea 300-meter beach which had appeared after 17th century).
These phenomenons don't show flood of seacoast and
don't prove increasing Greenhouse-effect either. The conclusions
can be different if the theory of increasing of the
earth size is accepted.
SANDRA O. BRIZGA 1 & IAN D. RUTHERFURD 2
Sedimentation in the Yarra Estuary, South-Eastern
Australia: geomorphology and management
1 s. Brizga & Associates, p.o. box 68, Clifton Hill Vic. 3068, Australia
2 Cooperative Research Centre for Catchment Hydrology,
Monash University, Clayton Vic. 3168, Australia
Sedimentation is a major management issue in estuaries throughout
the world, particularly in situations where the
maintenance of a navigable waterway is a management imperative.The
Yarra estuary is no exception. It falls into
two management regions: 1) the downstream end of the
estuary which has been developed as part of the Port of
Melbourne; and 2) the middle and upstream parts of the
estuary which are managed for a range of uses including
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power boating (tourist ferries and private boats), canoeing,
rowing, angling, passive recreation, and flood drainage.
This paper focuses on the Yarra estuary upstream of the
port.
The study area had been substantially modified since European
settlement. At the time of European settlement,
rock bars near the downstream end limited the intrusion of
tidal flows. The removal of the rock bars in the late nineteenth
century shifted the head of the estuary some 15 km
upstream. Other modifications have included.channel widening'
straightening, bank lining, and levee bank development.
The tidal regime has also been affected by port development
further downstream. Catchment development,
including flow regulation, has affected hydrologic regime
and sediment loads. These changes have had major impacts
on physical processes in the study area.
Historically, dredging has been carried out to remove
unwanted sediment deposits from the Yarra estuary,
although this approach has recently been queried on environmental
and financial grounds. A geomorphological investigation
was carried out to assist in answering management
questions such as:
- are there any feasible alternatives to dredging, such as
reducing sediment production at source or manipulating
patterns of deposition within the estuary?
- what would happen in the absence of any further management
intervention in the sedimentation processes (including
dredging)?
Data were obtained using a range of methods including coring
and probing of the river bed to examine the character
and distribution of the sediment deposits, dating of the sediments
on the basis of artefacts and pollen, and analysis
of historical documentary data such as bathymetric surveys
and dredging records to determine deposition rates. The
study also drew upon the results of recent geomorphological
investigations of the Yarra River further upstream. Some
key findings are outlined below.
The sediments recently deposited in the estuary are dominated
by muds and, to a lesser extent, sand. The sources of
the muds are diffuse, and include surface wash-off as well
as in-stream sources throughout the catchment. The major
sources of the sands are likely to be in parts of the catchment
close to the estuary. Catchment management will not
solve the problems of sedimentation in the short term, but
in the longer term is likely to be a useful part of an overall
management strategy, particularly in terms of limiting the
influx of pollutants bound to sediments.
A relationship was apparent between channel width and
deposition, the widest reaches displaying the highest deposition
rates. Other aspects of the pattern of deposition, such
as the development of point bar, alternate bar, and concave-bench
deposits, were predictable on the basis of geomorphic
principles. We concluded that dredging is necessary
where management requirements are in conflict with
natural sedimentation processes, such as where over-wide
reaches need to be maintained (e.g., for rowing or ferry
turn-around sites), or where deep water access is required
at boat landings situated on the inside banks of bends.
Hydraulic geometry analysis of the Yarra catchment and