ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

Britain. Engineering geomorphology is now in a second
phase of answering geomorphological questions, providing
geomorphological information and implementing
management in accordance with the principles advocated.
This is involving much case-study work at specific locations.
A third phase of major development in the future is
envisaged in this paper, mainly stemming from major
changes in geomorphology itself and underlain by radical
alterations of scientific theories, philosophy and methods.
This will involve modelling and predicting responses in
ways that adequately deal with complexity, positive feedbacks,
non-linearity and holism. Questions remain with regard
to the links between geomorphology and engineering
on the type of predictions that are possible and acceptable,
and on the extent to which geomorphology will provide
'solutions', both nationally and internationally. Whatever
strategies or solutions are suggested there remains the
issue of political acceptability in specific applications and
the need for mechanisms to make public gain compatible
with private loss. Geomorphologists arguably have the potential
for another major leap forward, stimulated by theoretical
and technological developments, in which the results
of research will feed directly into 'environmental engineering',
providing the requisite spatial and temporal
data are available.
P. KYLE HOUSE 1 & VICTOR R. BAKER 2
Unconventional methods for evaluating the magnitude
and frequency of flash floods in ungaged desert
watersheds: an example from Arizona
1 Desert Research Institute, Quaternary Sciences Center,
Reno NV, 89512 USA
2 Department of Hydrology and Water Resources, University of Arizona,
Tucson AZ, 85721 USA
The vast majority of streams draining small watersheds in
desert areas throughout the world are ungaged. Typically,
desert regions are also characterized by sparse or non-existent
networks of meteorological stations. Thus, determining
the magnitude and frequency of flash floods in these
areas from the basis of real meteorological and hydrological
data on flooding is often impossible. This situation prevails
in many portions of the deserts of the southwestern
United States where small, rugged desert watersheds are
ubiquitous and commonly situated in physical settings that
are preferred areas for suburban development along the
outskirts of rapidly growing urban areas, thus posing a significant
flood hazard.
A recently completed multidisciplinary study of the flood
hydrology of a relatively remote portion of the Sonoran
Desert in west-central Arizona has demonstrated the feasibility
of developing a fairly detailed catalog of the magnitu-
de and frequency of flash-flooding in a region with very little
conventional data pertaining to floods. In the study, techniques
of paleoflood hydrology, aerial photograph analysis,
archeology, and historical research were combined
with minimal regional hydrological and meteorological data
to compile a regional flood chronology from 9 small
drainage basins (7-70 km') in the Buckskin, Rawhide, and
Artillery Mountains of western Arizona. The flood chronology
documents flash-flood events that have occurred in
the region over a time scale ranging from less than 1 to more
than 1200 years.
The recent flood history of each site was preliminarily evaluated
through comparison of a series of aerial photographs
spanning 50 years. At least one set of photos was
available for each decade. Occurrences of large floods were
easily inferred from distinct photographic evidence for
flood related channel change between photo dates. Tighter
constraints on flood timing were obtained by comparison
of dates bracketed by the photo analysis with sparse regional
meteorological and hydrological information, production
dates of beer cans found in flood deposits, presence of
distinct anthropogenic horizons in flood sediments, postbomb
14C dates on flood transported organic detritus, and
collection of anecdotal accounts from the few residents of
the general area. Constraining the timing of recent events
enables the determination of the most likely flood-producing
hydrometeorological processes. In this region, intense
precipitation from isolated thunderstorms and dissipating
tropical cyclones appear to be of nearly equal importance.
This pattern is likely to be reflected in the paleoflood record
as well. Techniques of paleoflood hydrology were employed
at each study site to extend the flood record significantly
back in time and also to estimate flash-flood magnitudes.
The paleoflood history of each site was established
through stratigraphic analysis of flood deposits and 14C dating
of detrital and in situ charcoal collected from flood sediments.
Flash-flood magnitudes were estimated by incorporating
the relict high-water evidence (historical and paleo)
into a step-backwater hydraulic modeling routine.
Study sites were preferentially located in bedrock canyons
with tight downstream constrictions to aid in the hydraulic
modeling and to ensure the presence of paleoflood stratigraphy.
Less ideal sites were also evaluated to broaden the
spatial and temporal scope of the investigation.
The study results indicate a striking consistency among the
magnitudes of the largest floods in both the historical and
the paleoflood records. This accords with similarities noted
among paleoflood and recent flood magnitudes in much
larger drainage basins in this general region. The magnitudes
and relative frequencies of the largest flash-floods
documented in west-central Arizona are at variance with
100-year flood magnitudes predicted for the same region
by conventional regional-regression methods. This indicates
that the predictive equations do not accurately characterize
the flood hydrology of this region and may not be
appropriate for regulatory purposes. Collection of historical
and paleoflood information from the region of interest
is the only means for demonstrating such a discrepancy aside
from instituting a gaging network and waiting for large
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