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Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
63
DOI: 10.4408/IJEGE.2013-06.B-05
GLOBAL LOSSES FROM LANDSLIDES ASSOCIATED
WITH DAMS AND RESERVOIRS
D
aviD
PETLEY
Durham University - Department of Geography - Durham, UK
regions of Asia, a very large number of dam construc-
tion projects are proposed, planned or under construc-
tion. This suggests that losses will continue to rise in
the years ahead unless substantial measures are taken
to address the causes.
K
ey
words
: landslide, dam, reservoir, precipitation, loss
INTRODUCTION
The 1963 Vajont landslide represents the most im-
portant example of a dam-related landslide that caused
loss of life. Whilst details about the mechanisms of
failure remain controversial, the failure sequence and
causes are well-documented, as are the consequences
of the wave generated by the landslide when it entered
the reservoir (P
aronuzzi
& B
olla
, 2012). There is lit-
tle doubt that this event changed the ways in which
landslide hazards associated with dams have been
perceived and managed, and there has been no sub-
sequent dam-related event of this scale, despite many
large dam construction projects in high mountain
areas. Nonetheless, landslides associated with dams
continue to cause both loss of life and high levels of
economic cost. In summarizing the main causes of
failure of large dams, S
ingh
(1996) noted that 10% of
collapses result from slides of earth, rock and/or ice
from the flanks of the lake. Thus, this remains a prob-
lem that requires further work. This paper presents
a review of recent landslide events associated with
dams and reservoirs worldwide, with a focus on those
ABSTRACT
The 1963 Vajont disaster represents by far the
largest landside-related accident associated with a dam
or reservoir in recorded history. Since then, those in-
volved in planning and constructing large dams and
reservoirs have taken measures to ensure that this
event is not repeated. In general this has been success-
ful, with no events with losses on a similar scale. How-
ever, landslides have continued to present a substantial
challenge to those involved in the design and construc-
tion of large dams. In the first part of this paper, a brief
review is provided of the impacts of landslides on dam
projects, highlighting that although losses of life from
landslides on reservoir banks have been low, mass
movements have frequently caused problems for dam
foundations and abutments. Unidentified landslides or
areas of potential instability have required very expen-
sive mitigation works when identified after dam con-
struction had started, and they have caused substantial
environmental impacts. The second part of this paper
examines losses of life from landslides associated with
dams and reservoirs in the period 2003-2012 inclusive.
It is shown that during this time 500 lives have been
lost in landslides associated with dams and reservoirs
in 37 separate events. Almost all of these landslides
have occurred in East and South Asia, with the ma-
jority affecting India and China. These landslides have
mostly killed people involved in the construction of
dams, either at construction sites or in landslides af-
fecting workers’ accommodation. In the mountainous
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D. PETLEY
64
International Conference on Vajont - 1963-2013 - Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
on the flanks of reservoirs are much more common
though, and the peak of activity usually occurs during
initial impoundment and shortly thereafter, although
activity can continue for long periods of time. Finally,
landslides during the decommissioning of a dam site
are rarely considered but can be very important. The
change in the stress state can destabilise the flanks for
the reservoir and sediment impounded behind the dam
can become unstable, forming mudflows.
COSTS OF DAM-RELATED LANDSLIDE
DISASTERS PRIOR TO 1963
Although Vajont remains the best-known exam-
ple of a landslide associated with the construction of
an artificial dam, there is a number of documented
examples of previous events in the literature. Four
key events are reviewed here, demonstrating the high
costs associated with landslides at dam sites.
AN EARLY MASS FATALITY EVENT: THE 1864
DALE DYKE DAM FAILURE NEAR TO SHEF-
FIELD, ENGLAND
The collapse of the Dale Dyke Dam on the River
Loxley, upstream of Sheffield, England in 1864 caused
very high levels of loss, including about 250 fatalities
and £324,000 (the equivalent of $50 million in 2012
values) of direct economic costs. The city of Sheffield
and surrounding areas were flooded by the resulting
deluge. The inquest into the event heard conflicting
evidence about the likely cause of the failure, but evi-
dence was presented that the failure may have been
the result of a landslide that affected the toe of the
embankment. Evidence was presented to the jury that
the flank of the dam was subject to landslide-related
deformation prior to the collapse. A landslide remains
a likely possible cause of the collapse, although B
innie
(1978) argued that the failure may have been due to
fracturing in the clay core of the dam.
AN EXAMPLE OF UNANTICPATED LANDSLI-
DE IMPACTS: THE 1941 TO 1953 GRAND
COULEE DAM LANDSLIDES
The Grand Coullee Dam on the Columbia River
in Washington State, USA was completed in 1942
toprovide both irrigation and hydroelectric power.
The resultant lake is exceptionally long (232 km),
such that some landsliding was expected. However,
that cause fatalities, drawing upon information from
both the literature and the Durham Fatal Landslide
Database (DFLD). It shows that landslide-induced
losses remain unacceptably high, although in recent
years the majority of fatalities have been associated
with mass movements during the construction phase
of the dam. As there are plans to build large numbers
of dams in high mountain areas in the coming years,
greater attention will need to be paid on the mitigation
of landslide hazards if losses are not to increase.
PERSPECTIVES ON RESERVOIR-INDU-
CED LANDSLIDES
S
chuSter
(1979) reviewed landslides induced by
reservoirs, noting that the failure of slopes into lakes
can induce the following hazards:
(1) Water waves that can cause local damage
along the reservoir shoreline and, if overtopping oc-
curs, to structures downstream of the dam;
(2) Damage to the dam itself and to its associ-
ated infrastructure;
(3) Loss of storage capacity;
(4) Delays to the construction of the project.
In addition, landslides on the flanks of reservoirs
can cause environmental problems, such as the loss
of ecosystem services. Landslides impact upon dam
construction and operation at all phases of such a
project (Fig. 1), but the greatest impacts usually occur
in the construction and commissioning/impoundment
phases of a project. Thus, for example, in a review
of 254 examples in which landslides had generated
substantial problems at dam sites around the world,
S
chuSter
(2006) found that 78 had suffered from
ground movement of either an abutment or the dam
foundations. However, he cited only five examples
in which post-construction landslide movement had
threatened the integrity of the dam itself, and noted
that such cases are fortunately very rare. Landslides
Fig. 1 - A summary of the landslide impacts associated
with each phase of a major dam project
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GLOBAL LOSSES FROM LANDSLIDES ASSOCIATED WITH DAMS AND RESERVOIRS
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
65
of in excess of 150 m and in one case a volume of
over 1 km
3
(M
acfarlane
, 2009) To ensure the stabil-
ity of the flanks of the reservoir, a major programme
of engineering works was undertaken, involving but-
tressing (Fig. 2a), drainage (pumped and gravity), and
infiltration protection (Fig. 2b). It is estimated that the
costs of the landslide stabilisation and monitoring pro-
gramme were US$300 million (the equivalent of $470
million in 2012 values).
AN EXAMPLE OF A LANDSLIDE INDUCING
SUBSTANTIAL WATER QUALITY ISSUES IN A
WATER SUPPLY RESERVOIR PROJECT: THE
SHIHMEN RESERVOIR IN TAIWAN
The Shihmen Dam in Taiwan, which was com-
pleted in 1964, is located in Taoyuan County of north-
ern Taiwan, primarily for drinking water supply, irri-
gation and flood defence purposes. Since construction
the catchment area of the dam has suffered from a very
significant landslide problem (Fig. 3), which has led to
J
oneS
et alii (1961) documented a much higher level
of landslide activity than had been anticipated, with
about 500 landslides being observed in the period
between 1941 and 1953. Of these, 245 occurred dur-
ing the reservoir-filling period. Subsequent landslides
were mostly associated with periods in which the wa-
ter level was drawn down, supplemented by some as-
sociated with heavy rainfall. S
chuSter
(1979) noted
that although the total volume of landslide movement
is probably 50 - 100 million m3, economic losses have
not been high and there has been no loss of life. His
is attributed to: a. the comparably small size of the in-
dividual failures; b. the low population density of the
reservoir banks; and c. careful landslide management.
AN EXAMPLE OF A SMALL-SCALE, LAN-
DSLIDE-INDUCED DAM COLLAPSE WITH
HIGH CONSEQUENCE: THE 1955 ATENQUI-
QUE VOLCANICLASTIC DEBRIS FLOW AT
NEVADO DE COLIMA, MEXICO
On 16th October 1955, a volcanic debris flow
struck the town of Atenquique in Mexico (S
auceDo
et alii, 2008), triggered by three days of sustained
rainfall. The lahar originated as a series of multiple
landslides on the flanks of the Nevado de Colima vol-
cano, which coalesced within a steep series of ravines,
probably increasing in volume through entrainment
of basal materials within the channels. Downstream,
about 1 km prior to reaching the town of Atenquique,
the lahar encountered a 60,000 m
3
water storage res-
ervoir, which appears to have failed instantaneously.
At 10:45 in the morning, the town was struck by the
debris flow, which by this stage is thought to have had
a frontal height of 8-9 m. The landslide destroyed sev-
eral houses, a school, the local church, four bridges
and a paper factory. In total 23 people lives were lost.
AN EXAMPLE OF A VERY EXPENSIVE LAN-
DSLIDE MITIGATION PROGRAMME: THE
CLYDE DAM LANDSLIDES IN NEW ZEA-
LAND, 1989-1993
The Clyde Dam is an important 432 MW run-of-
the-river HEP scheme on the Clutha River in South
Island, New Zealand. During construction of the
project, 17 large prehistoric landslides were identified
on the flanks of the Cromwell Gorge, which was to
be impounded by the dam. Some of these landslides
were unusually large – for example with thicknesses
Fig. 2 - Two oblique aerial views of the Clyde Dam land-
slide mitigation works: a. A toe buttress on the
Brewery Creek landslide (landslide volume = 80
million m
3
); b. The innovative infiltration protec-
tion structure on the Cainmur landslide
Fig. 3 - Two views of the Shihmen Dam landslide catch-
ment. a) A landslide located on the catchment
valley walls); b. One of the many sediment check
dams upstream of the main reservoir, constructed
to retain sediment released by landslides. In this
case the storage capacity of the check dam is
now fully infilled
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D. PETLEY
66
International Conference on Vajont - 1963-2013 - Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
ly under-estimated in large-scale dam and reservoir
projects. However, it is also the case that the costs of
landslides are generally under-estimated in both finan-
cial and life terms.
GLOBAL LANDSLIDE FATALITIES 2004-2011
P
etley
(2012a) used the DFLD to investigate
losses associated with non-seismic landslides in the
period 2004-2010, reporting a total 2620 fatality-
inducing landslides that caused a total of 32,322 re-
corded deaths. Although this is an order of magnitude
higher than had been previously reported, this total
is likely to underestimate the total losses by a small
degree (probably 10-20%). The methodology used to
collect this data is described in detail in P
etley
et alii
(2005) and P
etley
(2012a and 2012b), but in brief in-
volves the use of newswire data, technical reports, of-
ficial datasets and scientific papers to track the occur-
rence of fatality-inducing landslides on a global basis.
The dataset includes all mass movements commonly
classified as landslides, including rockfalls and debris
flows, but not including snow and ice avalanches.
Here, an updated dataset is presented, with losses
for an additional year (2011), such that the dataset spans
the period 2004-2011 inclusive. In this period 35,287
landslide-induced fatalities were recorded in 3,059 non-
seismic events, representing an average of 4,411 fatali-
ties per year. Once seismically-induced landslides are
included in the total, the number of landslide-induced
fatalities increases to 84,341 (i.e. an average of 10,543
per annum), with this data being dominated by the land-
slides associated with the 2005 Kashmir and 2008 Wen-
chuan (Sichuan) earthquakes. Figure 4
presents the distribution of non-seismically-in-
duced landslide induced fatalities in the period 2004-
2011; as noted by Petley (2012a) the global landslide
distribution in the DFLD dataset is strongly heterogene-
ous, with the majority of landslides occurring in South,
large volumes of sediment entering the reservoir. In
consequence, the storage volume of the reservoir has
been reduced from 0.309 to 0.210 km
3
. Considerable
effort has been expended in trying to manage the land-
slides and to trap sediment before it enters the lake
with, for example, over 120 large-scale check dams.
In 2007, one of these failed, releasing 10 million m3
of sediment. The high suspended sediment level in the
lake has also caused a deterioration of water quality
due to the effects of eutrophication and turbidity (K
u
et alii, 2009). As a result a series of very expensive
mitigation programmes have been required.
As these examples show, the impacts of land-
slides on dam and reservoir projects are highly com-
plex and varied. For example, even small-scale dams
can be responsible for substantial loss of life when
they are affected by landslides. In addition, landslides
can inflict high unanticipated economic costs to large-
scale dam and reservoir projects, often causing cost
over-runs and delays to completion dates. In many of
the examples examined in detail by S
chuSter
(2006),
the remediation costs were very high - for example,
the 80 m high Tablachaca Dam in Peru was construct-
ed in 1972 on an ancient rockslide. In the late 1970s
the landslide, which formed the right abutment of the
dam, began to move. A complex set of remediation
structures, including an earth berm at the toe, rock
anchors and drainage tunnels, were constructed at an
estimated cost of US$40 million (the equivalent of
$84 million in 2012 values). There are many similarly
expensive impacts on dam and reservoir projects.
Finally, landslides can have substantial intangible
costs as well, for example damaging the recreational
value of the banks of the reservoir, as well as being
responsible in some cases for significant deterioration
of water quality through turbidity and eutrophication,
which can require extremely expensive mitigation
schemes. Thus, the impact of landslides is common-
Fig. 4 - The distribution of non-seismic fatality-inducing
landslides from 2004 to 2011, projected onto a
digital elevation model. Each dot represents a sin-
gle landslide that caused one or more deaths
Fig. 5 - The distribution of major dams worldwide as re-
corded in the GRanD dams database (L
ehner
et
alii, 2013)
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GLOBAL LOSSES FROM LANDSLIDES ASSOCIATED WITH DAMS AND RESERVOIRS
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
67
cidence in the DFLD dataset. However, in Asia these
very large dam / reservoir projects are generally located
in areas with high rates of fatality-inducing landslide
occurrence, suggesting a different level of landslide
hazard associated with these programmes in this region.
FATALITIES ASSOCIATED WITH DAMS AND
RESERVOIRS, 2003-2012
Using the DFLD dataset, the occurrence of land-
slides associated with large dams has been extracted
and is presented in Table 1. In total there are ex-
actly 500 recorded deaths in this dataset in 37 dis-
tinct events. The locations of these 37 landslides are
shown on Fig. 8, alongside the full fatality DFLD
dataset. The geographical distribution of the land-
slides is highly heterogeneous, with most of the
losses occurring in South and East Asia. Analysed
from a country-specific perspective (Fig. 9), loss-
es were recorded in only nine countries, of which
China and India account for 51% and 32% of the
losses of life respectively. The occurrence of these
South-East and East Asia, with the southern edge of
the Himalayas representing the largest global hotspot
for landslide events. Other hotspots can be found in for
example Central and parts of South America and in the
Caribbean. Most landslide hotspots in the DFLD data-
set are in poorer countries.
It is interesting to compare the distribution shown
on Fig. 4 with the distribution of large dams worldwide.
Figure 5 shows the distribution of large dams as mapped
by the Global Reservoir and Dam (GRanD) database
version 1 (2012) (l
ehner
et alii, 2013). This dataset
provides compiles reservoirs with a storage capacity of
> 0.1 km³. This version of the database contains records
of 6,862 reservoirs worldwide with a storage volume
of >0.1 km
3
. In Fig. 6, dams constructed since 1990 are
shown. It is notable that in this period the numbers of
large dams completed in North America and Northern
Europe was low, with significant numbers being built in
Asia and Southern Europe.
In Fig. 7 the distribution of very large reservoirs
(storage volume greeter than 1 km
3
) is shown, super-
imposed on top of the distribution of fatality-inducing
landslides for the period 2004-2011 as per Fig. 4. Note
that in most of the world these very large dams are
located in areas with comparatively low landslide in-
Fig. 6 - The distribution of major dams worldwide con-
structed since 1990 as recorded in the GRanD
dams database (L
ehner
et alii, 2013). Note the
comparatively large number that have been con-
structed in Asia and in S Europe
Fig. 7 - The distribution of non-seismic fatality-inducing
landslides from 2004 to 2011 (open circles) and
major dams (reservoir capacity >1 km
3
, black tri-
angles) from the GRanD dams database (v1 2012,
L
ehner
et alii, 2013), projected onto a digital el-
evation model
Fig. 8 - The distribution of fatality-inducing landslides as-
sociated with dams and reservoirs in the period
2003-2012. LEGEND: The small dots indicate
other fatality-inducing landslides for the period
2004-2011; the large dots present the landslides
associated with dams and reservoirs in the afore-
mentioned period
Fig. 9 - The recorded occurrence of fatality-inducing
landslides, as recorded on the DFLD dataset, as-
sociated with dam and HEP projects in the period
2003-2012 inclusive, organised by country. The
bar graph shows numbers of fatalities (right hand
axis), whilst the line graph shows numbers of re-
corded events (left hand axis)
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D. PETLEY
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International Conference on Vajont - 1963-2013 - Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
events in time possibly suggests an increasing rate
(Fig. 10), although the data are too short to properly
assess the trend. Note that 2007 stands out as a year
with an unusually large number of landslides and re-
sultant fatalities.
The brief description of the landslide events in
Table 1 demonstrates that many (46%) of the land-
slides took the form of landslides or rockfalls at dam
construction sites, but with 30% taking the form of
landslides or rockfalls that impacted upon workers’ ac-
commodation (Fig. 11). There were also five landslides
that affected workers either maintaining or travelling
on highways near to the construction site, and a small
number of landslides in quarries or spoil heaps. Only
one Vajont-style fatality-inducing reservoir bank land-
slide occurred, although this event killed 24 local peo-
ple and destroyed 129 houses and four factories. This
was the 14
th
July 2003 Qianjiangping landslide (Fig.
12), which occurred during the first impoundment of
the Three Gorges Reservoir (W
ang
et alii, 2004). The
landslide occurred as a rapid movement on a rock bed-
ding plane as the water level rose. This landslide had
been preconditioned to failure by quarrying activities
by a local brickworks from 1997-2003, and final failure
occurred in the aftermath of intense precipitation.
Many other landslides have been documented
along the banks of the Three Gorges Reservoir (e.g.
f
ourniaDiS
, 2007) and unanticipated efforts have been
required to manage and mitigate them. In early 2012
Liu Yuan, an inspector at the Ministry of Land Re-
sources in China reported that the number of landslides
along the banks of the Three Gorges reservoir had in-
creased substantially since the impoundment of the lake
began. He is reported to have observed that that 5,386
sites were being monitored, of which 355 locations had
already suffered landslides. The result is that an addi-
tional 100,000 people may need to be relocated from
the banks of the reservoir.
Fig. 10 The recorded occurrence of fatality-inducing
landslides, as recorded on the DFLD dataset, as-
sociated with dam and HEP projects in the period
2003-2012 inclusive. Numbers of fatalities (bar
graph, right hand axis) and cumulative numbers
of events (line graph,
left hand axis) show an in-
creasing trend with time, although 2007 does
stand out as an exceptional year
Fig. 12 - The Qianjiangping landslide on the banks of the
Three Gorges Reservoir in China. This landslide,
which was responsible for the loss of 24 lives, was
associated with the first impoundment event of the
Three Gorges Dam
Fig. 11 - The breakdown according to types for the occur-
rence of fatality-inducing landslides, as recorded
on the DFLD dataset, associated with dam and
HEP projects in the period 2003-2012 inclusive
Tab. 1 - Reported landslides associated with major dam
and HEP projects, as recorded in the DFLD da-
taset. In some cases the indicated dam project is
speculative as clear information is not available
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GLOBAL LOSSES FROM LANDSLIDES ASSOCIATED WITH DAMS AND RESERVOIRS
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
69
rates of weathering under tropical or semi-tropical con-
ditions; and affected by intense rainfall, especially in
the summer monsoon period. The importance of these
meteorological conditions is illustrated by the month of
occurrence of the landslides associated with reservoirs
or dams (Fig. 14). It is clear that the majority of these
landslides occurred during the northern hemisphere
summer when monsoon rainfall is dominating the
weather conditions of South and East Asia. This pattern
reflects that observed for this region for other fatality-
inducing landslides (e.g. P
etley
2010, 2012a, 2012b;
P
etley
et alii 2005).
A logical conclusion may well be that landslide
hazards associated with large dams in East and South
Asia are not being managed as well as might be opti-
mal. The reasons for this are likely to be complex and
varied, and may well include factors that are socio-eco-
nomic and/or political, and are thus beyond the scope
of this paper. From a technical perspective three aspects
may be important:
a. Occasional seismic activity can profoundly alter the
rates of activity of the landscape, such that condi-
tions that apply during a site investigation phase
may no longer be current during the construction
of the dam and associated infrastruccture;
b. In a tropical or sub-tropical landscape, there is fre-
quently a combination of thick layers of weathered
material and dense vegetation. This can render the
identification of potential or pre-existing landslides
very challenging. Thus, it is likely that many po-
tential instabilities are being missed during the site
investigation and planning phases;
c. The climate and geological environment of these ar-
eas are different to those in other areas in which
FUTURE PROSPECTS FOR LANDSLIDES AS-
SOCIATED WITH DAMS AND RESERVOIRS
The analyses presented here portray an interesting
view of landslides associated with dams and reservoirs.
The data suggest that since the 1963 Vajont disaster, the
dam and reservoir industry has in general been success-
ful in preventing recurrence of this type of accident.
However, two very clear patterns emerge:
a. In the planning phase of many dam and reservoir
projects there is a failure to recognise either the
existence of ancient landslide bodies (as indeed
was the case at Vajont) or to identify landslide po-
tential on reservoir banks. The upshot has been in
many cases project costs that have been substan-
tially higher than expected, and completion dates
that are later than planned;
b. In the construction phase of many projects, landslide
accidents continue to occur regularly. In many cases
these events are situated in or around construction
sites; landslides onto temporary camps are also
common. These events have been responsible for an
unacceptable level of loss of life in the last decade.
It is notable that the distribution of fatality-induc-
ing landslides associated with reservoirs and dams in
the last decade does not correlate well with the list of
dams completed in the same period (as indicated by
the GRanD dataset), even though nearly all landslides
occurred during the construction phase of the projects
(Fig. 13). The occurrence of these landslides in South
and East Asia appears to have been disproportionately
high in comparison with other areas. The cause of this
is not clear, but is likely to be associated with the level
of natural landslide activity associated with this geo-
graphic region. East and South Asia are both tectoni-
cally active (which is responsible for both generating
a landscape that is landslide-prone and for triggering
landslides through large earthquake); subject to high
Fig. 13 - A comparison of the distribution of fatality-induc-
ing landslides associated with dams and reser-
voirs (point symbols) with the distribution of large
dams completed in the period 2003-2012 (square
symbols) as indicated by the GRanD database
Fig. 14 - The number of recorded fatality-inducing land-
slides associated with dams and reservoirs by
month of occurrence in the period 2003-2012.
Note the higher incidence in the Northern Hemi-
sphere summer, which suggests a strong meteoro-
logical influence on their occurrence
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D. PETLEY
70
International Conference on Vajont - 1963-2013 - Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
coming years. Thus, without careful management there
is a strong potential for continued landslide impacts on
large dam and reservoir projects.
DISCUSSION AND CONCLUSIONS
The 1963 Vajont dam disaster undoubtedly repre-
sents a watershed moment in the management of land-
slides associated with large dams and reservoirs. Fortu-
nately, since the disaster there has been no repeat event
on a similar scale. However, landslides continue to be
a substantial issue in the planning and implementation
of large dam projects. S
chuSter
(2006) demonstrated
that in a large number of cases, landslides have caused
significant disruption to dam sites themselves, often
requiring expensive mitigation programmes to founda-
tions and abutments. Landslides on reservoir banks in-
flict substantial levels of loss, as the 2003 Qianjiangping
landslide on the Three Gorges reservoir demonstrates. It
is likely that the impact of landslides will continue for
many years in the Three Gorges reservoir. Fortunately,
to date only one of these landslides has been responsible
for loss of life, although great care will be needed in
exceptional rainfall events over the next few years.
However, it is clear that in recent years a sub-
stantial problem with landslides associated with dams
and reservoirs has developed. This is associated with
landslides that occur during the construction and im-
poundment phase of dam projects. Large numbers of
fatality-inducing landslides have been occurring, with
substantial levels of loss of life. The majority of these
landslides have occurred in South Asia and East Asia,
large dams have been constructed. In particular,
the dynamic nature of the landslide can be easy to
under-estimate.
In the coming years a very large amount of dam
construction is planned around the world as the need for
hydroelectric power increases for both social and envi-
ronmental reasons. Major hydroelectric power projects
are planned or proposed in high mountain areas on all
of the inhabited continents. However, the global centre
for large-scale dam and reservoir projects in the next
two decades will inevitably be South and East Asia,
with the steep valleys of the Himalayas being respon-
sible for a substantial proportion of that planned activ-
ity. Fig. 15 presents the distribution of fatality-inducing
landslides associated with dams and reservoirs, fatality-
inducing landslides for the period 2003-2011, existing
large scale dams from the GraND dataset and the distri-
bution of planned large-scale dams (data from i
nterna
-
tional
r
iverS
2013 and other sources). It is clear that a
very large number of new projects are planned in this
region in the coming years. In most cases these projects
will be constructed in areas that have been subject to
high levels of landslide activity in the past, such that
palaeo-landslide deposits are likely to be extensive.
Landslide activity under contemporary climatic condi-
tions is likely to be high, and most of this area is also
subject to occasional large or very large earthquakes,
which are likely to be associated with extensive land-
slide activity. Finally, the effects of climate change in
this area may be increased precipitation intensity (e.g.
P
etley
, 2010), which may increase landslide activity in
Fig. 15 A comparison of the distribution of fatality-inducing landslides associated with dams and reservoirs (point symbols)
with the distribution of large dams completed in the period 2003-2012 (square symbols) as indicated by the GRanD
database, the distribution of planned dams (crossed circles) and fatality-inducing landslides (small dots)
background image
GLOBAL LOSSES FROM LANDSLIDES ASSOCIATED WITH DAMS AND RESERVOIRS
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
71
mate change, and in particular increases in peak rainfall
intensity, will change patterns of landslide activity. At
least some of these sites are also likely to be affected
by earthquakes, which generate large numbers of land-
slides, during their design life.
Since the Vajont disaster, the dam and reservoir
industry has very successfully identified and mitigated
landslides, albeit at times at very high cost. A similar
level of action is now required to address landslides
occurring at and around dam construction sites and in
the camps housing the workers, especially in East and
South Asia. To do so will require concerted effort from
planners, funding agencies, regulators and construc-
tion companies.
ACKNOWLEDGEMENTS
This work was undertaken within the framework
of the International Landslide Centre (ILC), part of the
Institute of Hazard, Risk and Resilience at Durham
University. The DFLD was funded by an anonymous
benefactor to the ILC. The analysis of this dataset and
production of the paper was funded by NERC nd ESRC
through the Earthquakes Without Frontiers programme,
grant NE/J01995X/1.
and in particular on dam projects in India and China.
In most cases the victims have been people employed
by the dam project, with most of the landslides hav-
ing occurred either on construction sites associated
with the project or on workers’ accommodation sites.
Clearly, there is a need for improved management of
these sites to reduce the impact of landslides. At this
stage it is not clear as to whether these events might
indicate that there is an increased chance of landslides
during the impoundment phase of these large dam
projects.
As Fig. 14 demonstrates, in coming years there are
many further large-scale dam and reservoir projects
planned for landslide-prone areas. There is a notably
high number of these projects planned for the Hima-
layan region, which is both highly landslide-prone and
has a track record of large landslide events associated
with reservoirs and dams. Landslides associated with
these projects have the potential to continue to gen-
erate substantial human and economic losses unless
improvements are put in place to reduce to reduce the
occurrence of landslides at and around the dam con-
struction sites. In the areas in question, it is also likely
that changes to weather patterns associated with cli-
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