2. The reservoir dam represents a
particular source of high vulnerability
a point of conjunction between natural
and anthropogenic disaster potentials.
3. Types of reservoir dam:
• earth dam and rock-fill dam
(embankment dam): triangular section,
built of compacted sediments and
boulders (most common type)
• gravity dam: weight of concrete or
dressed stone supports structure
• concrete arch dam: deflects pressure
of impounded water onto adjacent
foundations and abutments
• buttress dam: has supports
on its downstream side.
4.
5. Fewer than 10%
of dams are
made of concrete
Worldwide:
• more than 50,000 dams are higher
than 15 m
• more than 40 are higher than 180 m.
6. Dams and reservoirs are used for:-
• water supply for domestic
and industrial use
• electrical power generation
• reduction of flood risk
• acquifer recharge
• irrigation and agricultural uses
• recreation (tourism and sport).
7. Problems:
• pollution of stored water
(with sediment, etc.)
• loss of storage capacity (siltation,
leakage or breaching of dam)
• seiching in violent windstorms or
earthquakes (seiche: a oscillatory
motion of an enclosed body of water)
• surges and water waves
caused by landslides.
8. Problems (contd.)
• failure of the dam leading to floods
• instability beneath the foundations
• overtopping if sluices or spillway fail
• loss of free board (caused by
subsidence or uplift)
• creation of earthquakes.
9. Brief classification of emergencies
associated with reservoir dams:
• filtration: slow loss of water, brief
and without serious consequences
• rapid loss of water through piping,
cracks or in highly permeable terrain
• partial or total collapse of the dam.
10. More than 2000
catastrophic failures
have been recorded
• 10% in the
20th century
• more than 9000
dead in the
20th century.
11. According to a study
of 308 dam disasters:
• 40% were caused by foundation failures
• 23% resulted from spillway failures
• 37% were due to errors of design
or construction, site inadequacies,
subsidence or earthquakes.
12. Disasters have resulted from:
• poor design, construction and
maintenance (foundation failures,
inadequate spillway capacity)
• site inadequacies
• extensive rains and swollen rivers,
leading to flood discharges
• earthquakes
• landslides.
13. To design safe dams:
• locate dam away from active faults
• overdesign to allow for displacements
• use wide sections that resist cracking
• use self-healing materials
• conduct geological and geotechnical
site survey
• design dam to resist elastic and
permanent displacements.
14. Case histories
St Francis dam, California, 1928
• 46.5 million m3 of water released
at 11,00014,000 m3/sec
Baldwin Hills Reservoir, Calif., 1963
• 5 dead and $15 million of damage
• faulting and subsidence: leakage -->
cracks --> collapse of earth dam.
17. Case histories
Teton Dam, Idaho (1976)
• 302.8 million m3 of water released
• 14 dead, $4001,000 million of
damage
Stava Valley, Italy (1985)
• collapse of two earth dams
• 264 killed in mudflow 5 km long
21. Case histories
Vajont Dam, Italy (1963)
• 1,925 dead, 3 villages flattened
• 240 million m3 of rock slid at
100 km/hr into reservoir
• wall of water 100 m high
29. Seismicity caused by tectonic
forces can cause:-
• liquefaction:
- of the foundations of the dam
- of earth dams
- of the reservoir sideslopes
• elastic or permanent displacements
and overtopping of the dam
• direct damage to the dam and collapse.
30. Earthquakes and reservoir dams
San Fernando Valley earthquake,
California (1971)
• M=6.1 earthquake nearly caused
• failure of the Van Norman (earth) Dam
• 80,000 people were at risk
32. Induced seismicity:-
• occurs where hydraulic conductivity
in underlying rocks is high
• high pore water pressures cause
rapid fault movements to occur
• the weight of water, if
its depth exceeds 100 m
• induced seismicity does not only
occur in areas of natural seismicity
• earthquake can occur some
years after the dam is built.
33. Dam Height Volume Year of Year of Magni-
of dam of water const- biggest tude
(m) (mn m3) ruction quake
Koyna,
103 2,708 1964 1967 6.5
India
Kremasta
165 4,750 1965 1966 6.3
Greece
Xingfeng
xang, 105 10,500 1959 1962 6.1
China
Oroville,
236 4,295 1968 1975 5.8
California
Kariba,
128 160,368 1959 1963 5.8
Zimbabwe
Hoover,
221 36,703 1936 1939 5.0
Arizona
34. Earthquakes and reservoir dams
Koyna Reservoir, India (1967)
• capacity 2,800 million m3
• filling of reservoir caused M=6.2
earthquake
• 177 killed and 2200 injured
35. Natural dams
• most natural dams fail within two
weeks of formation
• landslide debris or glacier ice
blocks river and causes impoundment
of discharge
• high pore water pressures cause
failure of dam
• failure usually leads to an
outburst flood.
41. Collapse of a dam
in the Chi-Chi, Taiwan,
1999 earthquake
42. Planning measures:
• surveillance of small dams,
not only large ones
• careful study of various risks
(earthquake, landslide,
subsidence, flood, etc.)
• careful study of the environment
of the dam and the reservoir
• geotechnical testing.
43. Planning measures:
• control of the techniques
of design and construction
• analysis of risks
• monitoring of risks
• evacuation plans for the
downstream valley area.
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