ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

data. Based on Equation 1, we reformulate Tokunaga's
concept of self-similarity for drainage networks, in a way
that incorporates both geometric and topologic features.
Our definition does not use the notions of Strahler's orders
and streams, which are not well defined in self-similar
topographies. We also show that many natural river profiles
are consistent with H(x,y,t) satisfying Equation 1 with
8 = O. In the past, different conclusions were reached on
the self-similarity of such profiles, based on self-similarity
conditions different from Equation 1. Finally, we show in
which sense river courses and width functions are self-similar.
GEORGE VENI
Methods and problems in conducting hydrogeologic
vulnerability assessments in Karst Areas
George Veni & Associates, 11304 Candle Park, San Antonio,
Texas 78249-4421, U.S.A.
Karst aquifers are the most sensitive to groundwater contamination.
Historically, such problems have been limited to
small and rural areas, but recent urbanization of karst terrains
has increased the risk and frequency of pollution, and
especially increased the need for hydrogeologic assessments
appropriate to their aquifers. Dye tracing is an important
and often-used technique in conducting vulnerability
assessments of karst sites, and is well documented for
its utility in delineating groundwater flow paths and conditions.
Geophysical techniques have also been used to assess
.karst areas. However, their precision varies according
to local conditions, they are best suited to locating the relatively
larger subsurface features, and broad areal use of
these methods is often very expensive.
Increasing numbers of urban karst site assessments are
being made solely by morphological examination of surface
karst features, although until this paper, effective standardized
techniques for such evaluations had not been
proposed. A case study of over 700 caves and karst features
along the southeastern margin of the Edwards Plateau,
Texas, U.S.A., supports the following geomorphological
karst feature assessment methodology outlined by the following
critical elements:
1. identify strata with greater secondary solution;
2. identify fracture orientations with greater secondary
solution;
3. develop an evolutionary model for the karst aquifer and
apply it to interpreting feature vulnerability;
4. determine if a feature has airflow;
5. note that features with no soil or with A horizon soil infills
are more likely to rapidly transmit contaminants
into the aquifer than features infilled with soils of the B
and C horizons;
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6. delineate the drainage basin of each feature, and its
likely relationship to other local recharge features;
7. excavate as needed for more accurate evaluations of the
features.
While the above methodology is effective at identifying
vulnerable karst features and areas, it alone will not prevent
groundwater degradation. Data clearly show that karst
aquifers can be readily contaminated if pollutants are
present on the karst surface, and that karst vulnerability assessments
only identify the most sensitive sites in these highly
sensitive terrains. Successful management of karst in
urban environments is best achieved by preserving the most
vulnerable areas and their drainage basins in their natural
state, coupled with minimizing pollutant loading of the
aquifer by limiting impervious cover to 15%.
CHRISTINE VERGNOLLE-MAINAR
Nouvelles technologies et rehabilitation des formes
de relief dans les etudes de geomorphologic
Geode, Umr 5602 Cnrs
Iufm, 181 avenue De Muret, 31 077 Toulouse Cedex, France
Les nouvelles technologies fournissent de nouveaux outils
d' analyse et permettent ainsi de vitaliser certains champs
de la geomorphologic. Elles sont aussi etroitement liees a
une evolution dans la facon de considerer l'objet des etudes
geomorphologiques, le relief.
L'utilisation de Modeles Numeriques de Terrain permet
une nouvelle representation graphique du relief. Ils proposent
une visualisation en trois dimensions sous de multiples
angles de vision. Et dans leur utilisation la plus frequente,
ils gomment les asperites de petite taille et privilegient
les grandes masses, leur morphologie generale et leur
agencement. Ils permettent egalement des changements
d' echelles, sans rupture de 1'une al' autre, et incitent arelativiser
l'opposition entre creux et saillants, une meme forme
pouvant etre 1'un ou l'autre suivant le niveau considere,
Cette nouvelle facon de representer le relief favorise un retour
en force des formes, de leur geometric et de leur agencement.
Un nouveau regard rehabilitant le relief pour luimeme
est done en train de se forger. Ceci est a mettre en
relation avec Ie fait qu'au cours de 1'histoire les modifications
majeures dans la representation de l'espace (comme
l'utilisation de la perspective) ont accompagne ou precede
un changement dans la facon de le concevoir. Le maniement
d'images en trois dimensions est une de ces ruptures.
Cette approche rompt en effet avec celIe de la geomorphologie
classique davantage centree sur la genese des formes,
sur la chronologie et les rnodalites de leur faconnement.
Dans le meme temps, emerge une demande derivant des
preoccupations environnementales et portant sur une meilleure
connaissance de la fonction des formes de relief dans
l'organisation et le fonctionnement des milieux. En effet,