and Gillette (1993). Dam breaching and the hydraulics of dam-break
floodwaves are discussed in some depth in Vischer and Hager (1998).
Time-dependent floodwave propagation downstream of a breached
dam is extremely complex. It is a function of site-specific parameters
including reservoir capacity and breaching characteristics for the dam
under review, e.g. the progressive erosion of an embankment, as at Teton
or, at the other extreme, the sudden monolithic collapse of the Malpasset
arch dam. The advance of the floodwave across the floodplain will in turn
be governed by a further range of determinants, many difficult to replicate
in a mathematical model, e.g. differences in terrain and surface, including
the influence of urban development and/or vegetative cover. Certain of
the difficulties inherent in modelling the floodplain adequately have been
eased with the advent of digital mapping techniques, but considerable spe-
cialist expertize and computational effort is required to produce a high-
quality mathematical representation of the breach development process
for an embankment and of the subsequent floodwave as it spreads across
the floodplain. Sophisticated commercial software is now available for
dam-break analysis and the preparation of downstream inundation maps,
much of the software deriving from the early ‘DAMBRK’ and ‘DAMBRK
UK’ programs (Fread, 1984 and DoE, 1991a, 1991b). Later dam-break
modelling programs include FLD-WAV (Fread and Lewis, 1998) and the
recently developed HEC-RAS. An overall review of dam-break flood
analysis methodologies is published in ICOLD (1998); simplified predic-
tive equations for estimation of the dam-break flood are presented in
Zhou and Donnelly (2005).
The European CADAM (Concerted Action on Dam-break
Modelling) project reviewed dam-break modelling practice in depth and
identified questions regarding performance (Morris, 2000). Particular
attention was paid to the two critical issues of breach formation and
floodwave propagation, with results from physical and computer model-
ling of the latter extrapolated to real valleys and calibrated against records
from the 1959 Malpasset arch dam failure. Guidelines and recommenda-
tions for modelling derived from the CADAM project are published in
Morris and Galland (2000). Following the conclusion of CADAM a suc-
cessor European project, IMPACT (Investigation of Extreme Flood
Processes and Uncertainty), included within its scope further investigation
of the central issues of breach formation mechanism and floodwave propa-
gation. The programme included a study of breach formation through a
series of 22 small-scale (0.6 m high) laboratory models and, in the field, a
series of five controlled breachings on embankments of 4.5 m to 6 m height.
Alternative dam sections, some homogeneous section some not, some
employing cohesive and others non-cohesive soils, were studied in the two
series of tests. The project outcomes are presented and discussed in
IMPACT (2005).
Dam-break inundation mapping exercises have now been conducted
amelia
(Amelia)
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