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CUDAM
CUDAM is a Center for advanced studies of hydrogeological
risks of mountain areas, with particular reference to
sediment production, hillslope hydrogeology, debris
and mud flows dynamics, alluvial fans and piedmont risks
issues.
Up to now, these phenomena have been analyzed separately
inside different disciplines and usually with focus
on single aspects. It is urgent, important and possible
to arrive to a set of conceptual, numerical and practical
tools that present scientific rigor with an interdisciplinary
approach. In particular, we are referring to generation
and modeling of shallow landslide and debris flows,
to the problems related to the evaluation in continuous
time of the hydrological cycle, to solid discharges
evaluation, to limited area precipitation forecasting,
to the morphology of the mountain and piedmont rivers,
to the role of vegetation on these phenomena. The Center
is the framework in which researchers of the disciplines,
that bring knowledge to the above phenomena, can jointly
work: low atmospheric physics, hydrology, geology, forestry,
topography, remote sensing and hydraulics. The Center
wants to coordinate multidisciplinary researches on
these fields and, at the same time, establish as a Center
for advanced education for graduate and postgraduate
national and international students. It will also support
life-long education for technicians and professionals
already working in the field of hydrogeological hazard
prevention with national and international scope, including
third world countries and especially Latin America.
An important aspect of the Center is the possible application
of the outcomes of the Center activities to basin planning,
risk prevention, evaluation of the efficiency of the
protection structures that could be implemented in collaboration
with public institutions: Provinces, River Authorities,
Ministries.
The Center is using the infrastructures of the Hydraulic
laboratory being completed at present, some experimental
basins, a computer center of the Department of Civil
end Environmental Engineering and the lodging facilities
of the University of Trento.
Furthermore, CUDAM is a Center of advanced studies for
the hydrogeological risks of mountain and piedmont regions.
Mountain areas cover nearly two thirds of the Italian
territory and require specialized studies. Both liquid
and solid discharges form in these areas and strongly
interact, making it necessary to approach the two aspects
jointly.
Mountain regions have been considered until a few years
ago marginal areas, mainly because of their scarce relevance
for the economy of the country. Actually, they were
areas devoted to sheep-rearing activities, in which
emigration has been the most attractive perspective
for young generations for a long time and which were
therefore subject to increasing depopulation. Starting
from the sixties, the increasing of the birth rate and
the increased prosperity allowed a great development
of tourism and handicraft. In a few ten years these
regions have taken on an important economic role. This
phenomenon has caused the stopping of emigration and
a progressive increase of urbanization, inclusive of
tourist activities, handicraft and minor manufacturing
and housing. This transformation changed the fragile
hydrological equilibrium of the mountain regions: there
has been not only an increase of natural catastrophes
because of the new anthropic pressure and of the progressive
abandon of soil maintenance practices, but also a uncontrolled
increase of costs of the damages of the properties and
of human lives.
Differently from what happens in plans, the hydrological
risk of mountain and piedmont regions depends on solid
supply and the intensity of the solid discharge implies
that it is not possible to approach the two components
separately. It is possible to think that the intense
run-off picks up the sediments and debris along the
hillslope and the bed of the torrents creating large
solid discharges, which could be (for small basins)
even ten times the liquid discharges (in form of debris
or mud flows). The solid phase starts to deposit in
the alluvial fans causing over-flooding phenomena that
damage anthropic settlements. Furthermore, the finest
part of the solid discharge flows down into piedmont
rivers, causing an increase of the water level that
often lead to over-flows because of the reduction of
the discharge capacity as the events of Versilia and
Garfagnana (Italy) in 1996 and Venezuela in 1999 teach.
The sediments transport in piedmont rivers is also a
determinant element causing localised erosion processes,
altering the river morphology and the environment.
The research activities can be summarised
as follows:
1. Hillslope instability and solid
run-offs formation.
Several researchers proposed empirical
approaches based on the relationships between rainfalls
and sediments volumes (Rickemann, 1997). Systematic
investigations on this topic has been carried on by
the research group led by Takahashi of the DPRI of the
Kyoto University (Japan): its geomechanical approach
is still important but subject to the simplifications
introduced into the geologic and stratigraphical structure
of granular deposits. A distributed approach that fully
uses the potential of high resolution digital elevation
models has recently been proposed by Dietrich et al.
(1992, 1995) . A research of the proponents shows that
the coupling of rainfall forecasting with soil water
contents models and simple hillslope stability models
with those data sets (DEMs) allows to foresee traslational
shallow landslides and debris flows.
The goal of CUDAM is modelling the mechanisms of infiltration
and water flow along hillslopes and in the alluvial
fans. High resolution digital models of the terrain,
satellite data, field measurements in the framework
of new hydraulic and geometrical models of the soil
(Heimsath et al., 1997) will be used. Another goal of
the proponents, at present involved in an ASI-NASA international
project, is to develop standardized data treatment techniques.
They require improved procedures of signal reconstruction
and topographic validation, also by means of sensors
able to return the microtopography and other information
related to vegetation.
2. Debris flows and hyperconcentrated currents dynamic
and mathematical models for mapping debris flow risk
and for evaluating the defence structures stability.
The first systematic approaches to intergranular
actions on the rheology of the granular fluids have
been proposed by Bagnolg (1954). Other researchers have
proposed rheological models which consider debris flows
as an equivalent single-phase fluid, a two-phases or
multi-phases fluid or as particles (McTigue, 1982; Jenkins
and Savage, 1983; Savage and Sayed, 1982; Johnson, 1987).
There is no reliable physical confirmation of the proposed
models.
The proponents have recently created an experimental
device (EC projects DEBRIS FLOW and THARMIT) for reproducing
stationary and uniform free surface flows for high concentrated
fluxes on an erodable bed in equilibrium (Armanini et
al, 1999). Compared to previous researches in anular
conducts (Bagnold, 1954) and in pressure pipes (Bakhtiary
and Asano, 1998), this system led to innovative results.
Furthermore, the new device allows more precise measurements
of the concentration and the velocity of the two phases
and of the granular temperature. The goal of CUDAM is
to define and characterise hyperconcentrated currents
and debris and mud flows rheology and to individuate
the global relationships existing between geometrical
and average physical quantities. This will allow the
definition of more precise and realistic mathematical
models integrated on the flow depth and able to more
exactly simulate the phases separation problem (Takahshi,
1980; Julien and O'Brian, 1988; Armanini, 1999; Fraccarollo
and Armanini, 1999). CUDAM will concentrate mainly on
two-phases modeling, also developing some physical simulations
to be used as tests for mathematical models.
3. Analysis of the morphological
phenomena relative to piedmont rivers.
Flow and sediment transport processes
which are relevant for the hydrological hazard prevention
of piedmont settlements will be investigated. As for
the long term morphological evolution of alluvial channels,
starting from the original contribution of de Vries
(1965), several refined approaches have been introduced,
both for general aspects and for particular aspects
which are relevant for the morphology of upper-middle
reaches like the bed response under unsteady flow conditions
(Tubino,1990; Welford, 1994) and the effect of sediment
heterogeneity (Gallapatti, 1983; Ribberink, 1983; Armanini
e Di Silvio, 1988; Holly and Rahuel, 1990; Lanzoni and
Tubino, 1999): in this context an original approach
to the concept of active layer (Hirano, 1972), which
has been mostly used up to now, has been introduced
by the proponents (Armanini, 1991). A second relevant
aspect is the planimetric configuration of rivers, both
for the theoretical implications and for the consequences
in terms of the hydraulic safety due to the strategic
role of river morphology and of the interaction processes
between flood plains and bed cuts (Shiono and Muto,
1998). Piedmont rivers present single thread meandering
morphologies or multi-channel braiding morphologies.
The factors determining the two morphologies are still
being studied (Langbein and Leopold, 1964; Ikeda et
al., 1981; Parker et al., 1982; Blondeaux and Seminara,
1985; Tubino and Seminara, 1990; Seminara and Tubino,
1992; Murray and Paola, 1994; Zolezzi and Seminara,
1999).
Aim of CUDAM is to investigate thoroughly
the evolution of braided rivers. The planimetric evolution
is influenced by the interaction with the banks and
the riparian vegetation which constrain the transport,
condition the resistance to flow, the pollutants dispersion
and river self-purification. Aim of the research is
to support projects of river renaturalization, frequently
proposed without an adequate investigation of the morphodynamic
processes which are involved. From an analytical and
numerical point of view, the mechanisms controlling
the dynamic evolution of braided rivers (bifurcations,
confluence, altimetry evolution of the single branches
of the river network) will be studied, in order to acquire
the fundamental knowledge for implementing mathematical
models of the whole network, with laboratory experiments.
For what field measurements are concerned, a braided
river reach, located in Trentino or Veneto regions,
will be monitored (Tagliamento River, Rio Solda). A
further aspect, which has recently became of great importance
mainly for bio-engineering restoration techniques, is
the interaction between vegetation, hydrodynamics, sediments
transport and river morphology. These studies will be
based on the field activity in the Sunwapta River, carried
out in collaboration with Canadian and American researchers.
It will give parameters for the validation of mathematical
and numerical models and for the evaluation of the reproducibility
of the involved process at laboratory scale.
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