ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

Depressions and similar features in the sample area were
described previously as forms of geochemical origin but
only recently they have been studied in detail. As in other
humid tropical areas these karstic-like forms evolve by vertical
exportation of soluble material from the base favoured
by lithological or tectonic discontinuities. More detailed
research is needed yet dominance of geochemical evolution
of landforms in southeastern Brazil must be accepted
and a landscape evolution model homologous to etchplains
evolution should be adopted.
ARTHUR J. CONACHER
Geomorphology and EIA in relation to agriculture
Department of Geography, University of Western Australia,
Nedlands, WA 6907, Australia
Dryland agricultural practices set in train a very complex
array of direct and indirect effects on the environment.
Many of these effects take place in the soil or affect the
soil, with the driving processes being pedological, hydrological
and geomorphic in nature.
Clearing of pre-existing vegetation in order to plant crops
or pasture affects the way in which rainfall reaches the soil
surface, by modifying interception, canopy drip (throughfall),
stemflow, storage in the biomass, drop impact, and
evapotranspiration. Pedo-geomorphic processes of rainwash
(rainsplash plus overland flow), infiltration and throughflow'
and the translocation of soil materials by those
processes and mass movements, are also influenced by vegetative
changes as well as by the range of Dryland agricultural
practices: including ploughing and seedbed preparation,
weeding, seeding, fertilising, spraying and harvesting;
and soil disturbances caused by the movements and grazing
activities of stock.
Secondary salinisation of soils and water in Australia is one
of the environmental consequences of dryland agricultural
practices, and the mechanisms which are responsible for
the problem show the need for an appreciation of both
geomorphology and hydrology. Intensely and deeply
weathered soils, deep and shallow aquifers, overland flow
and streamflow are crucial, and are illustrated by data from
the Western Australian wheatbelt, Geomorphology is relevant
both for understanding the processes and for correctly
'reading' landscapes in order to predict the future occurrence
of secondary salinity. In this latter context, landscape
interpretation is being assisted by remote sensing,
both in the traditional imaging sense and by the use of airborne
sensors to measure electrical conductivity and magnetic
anomalies, often in association with Gis.
There are several implications of this work in relation to
environmental impact assessment. The implications include
the inadequacy of most current Eia methodologies in
the agricultural context for accurately identifying and un-
derstanding processes. The environmental impact matrix
and its numerous derivatives, for example, are particularly
inappropriate. Secondary salinisation in dryland agricultural
areas, as is undoubtedly true for most environmental
impacts of agricultural practices, is not a simple cause-effect
situation.
A further implication concerns management. Accurate
identification and quantification of processes is essential if
effective remedial works are to be developed. Again with
reference to the secondary salinity problem, for many years
the standard remedial measure recommended to farmers
was to fence off the affected area (in order to control grazing
by stock) and to establish salt-tolerant vegetation.
Whilst this approach may improve the aesthetics of the site'
reduce erosion by water and wind, and provide at best
some fodder for carefully controlled light grazing, it does
not and cannot deal with the causes of the problem. These
occur in the catchments of the salt-affected areas, connected
to the latter by hydro-geomorphic processes, and influenced
by land-use practices. Thus it is in the catchments
that the processes must be manipulated by modifying landuse
practices in order to rehabilitate the salt-affected areas.
Manipulation takes place by essentially engineering-type
approaches as well as by agronomic measures, both designed
to control water movements on the slopes. Transpiration,
deep infiltration, throughflow and overland flow are
the main water movements targeted. In turn, if manipulation
is successful, the depth of groundwater tables from
the soil surface in salt-affected areas is increased, the translocation
of saline water to the surface by capillarity and
suction reduced, the accumulation of soluble salts in the
root zone prevented, and leaching of the soil by fresh
rainwater in the same zone enhanced, resulting in complete
rehabilitation.
CARMELO CONESA-GARCIA, FRANCISCO LOPEZ-BERMUDEZ,
FRANCISCO ALONSO-SARRIA & YOLANDA ALVAREZ-ROGEL
Hydraulic and morphological effects of the derivation
Tagus-Segura Works on the ephemeral channels
in the Rambla Salada Basin (South-East Spain)
Departamento de Geografia Fisica, Universidad de Murcia,
30001 Murcia, Spain
The Rambla Salada basin (131,6 kms"), situated in the semi-arid
zone of South-East Spain, is drained by a system of
ephemeral channels with a torrential regime, part of which
have already suffered the initial effects of the engineering
works being carried out in connection with the 'Right Canal
of the Tagus-Segura Aqueduct'. The building of the
infrastructure was started as recently as 1979, and it is of
great socio-economical importance for the agricultural
areas of the South-East of Spain. In this work the changes
brought about by the related structures (bridges, pipe-lines
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