Post on 02-Sep-2018
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Tracey Williamson
Associate Director | Water (Dams & Reservoirs)
British Dam Society Chairman
Historic dam failures and recent incidents
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1. Dams in all their beauty
2. Hazards associated with dams
3. History of dam failures around the world & in the UK
4. Links to UK dam safety legislation & guidance
5. Recent ‘near misses’ & incidents
Agenda
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Hazards and dam failure modes
Overtopping
Instability Internal erosion
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Hazards and dam failure modes
Foundation failure & appurtenant works failure
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Hazards and dam failure modes
Spillway failure
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History of dam failures around the world
Dam Dam
type
Country Height
(m)
Reservoir
volume
(106 m3)
Date
built
Failure Deaths
Date Type
Vega de Tera CMB Spain 34 7.8 1957 1959 SF 144
Malpasset CA France 66 22 1954 1959 FF 421
Vaiont CA Italy 265 150 1960 1963 L 2600
Baldwin Hills Emb USA 71 1.1 1951 1963 IE 5
Frias Emb Argentina 15 0.2 1940 1970 OF >42
Teton Emb USA 93 356 1975 1976 IE 14
Machhu II Emb India 26 100 1972 1979 OF 2000
Bagauda Emb Nigeria 20 0.7 1970 1988 OF 50
Belci Emb Romania 18 13 1962 1991 OF 25
Gouhou Emb China 71 3 1989 1993 IE 400
Zeizoun Emb Syria 42 71 1996 2002 OF 20
Shakidor Emb Pakistan -- -- 2003 2005 OF >135
Situ Gintung Emb Indonesia 16 2 1933 2009 IE 100
Dam type: CA = concrete arch, CMB = concrete and masonry buttress, Emb = embankment.
Type of failure: IE = internal erosion, FF = foundation failure, OF = overtopping during flood,
SF = structural failure on first filling, L = landslide into the reservoir causing overtopping
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Malpasset arch dam failure in France in 1959 (421 deaths)
The causes: High uplift pressures following heavy rainfall & a weakness in the left abutment rock
History of dam failures around the world
Lessons learnt:
Appropriate SI
and assessment
by experts in all
areas of dam
design
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Vaiont dam overtopping incident in Italy in 1963 (2600 deaths)
History of dam failures around the world
The causes: Instability of reservoir slopes causing a landslip & 125m high wave over the dam
Lessons learnt: Measure pore water pressures & movements at depth as well as at the surface
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History of dam failures in the UK
Dam Height
(m)
Reservoir
volume
(103 m3)
Date
built
Failure Deaths
Date Type
Tunnel End 9 1798 1799 OF 1
Diggle Moss (Black Moss) 1810 1810 OF 6
Whinhill 12 262 1828 1835 IE 31
Brent (Welsh Harp) 7 1837 1841 OF 2
Glanderston 1842 OF 8
Bold Venture (Darwen) 10 20 1844 1848 OF 12
Bilberry 29 310 1845 1852 IE 81
Dale Dyke 29 3,240 1863 1864 IE 244
Cwm Carne 12 90 1792 1875 OF 12
Castle Malgwyn 1875 OF 2
Clydach Vale 1910 OF 5
Skelmorlie 5 24 1861 1925 OF 5
Eigiau &
Coedty
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11
4,500
320
1911
1924
1925
1925
FF
OF 16
Type of failure: IE = internal erosion, FF = foundation failure, OF = overtopping during flood
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History of dam failures in the UK
Dale Dyke dam breach in 1864 (244 deaths)
The causes: Internal erosion possibly caused by hydraulic fracture of the core
Lessons learnt: Designs include wider cores, use of cohesive & compacted fill and placing pipes in tunnels through natural ground
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Dam failures Developments in legislation & guidance
Dale Dyke
(244 dead) in
1864
1864: Designs include specifications for fill to be
worked in layers not exceeding 0.23m
1872: Tunnels driven through natural ground
Upstream valve control on pipes through dams
Incidents of
leaks through
foundations in
the 1870s
1876: First use of concrete cut-off trenches
1879: First use of grouting to seal foundations
1882: Vyrnwy dam designed with a drainage
tunnel network to reduce uplift pressures
Links to UK dam safety legislation & guidance
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History of dam failures in the UK
Eigiau & Coedty dam failures in 1925 (16 deaths)
The causes: Foundation failure of Eigiau & overtopping failure
of Coedty
Lessons learnt:
Dams need to be designed, supervised and inspected by qualified engineers
Eigiau dam failure
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Coedty dam failure
Devastation in
Dolgarrog 1925
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Links to UK dam safety legislation & guidance
Dam failures Developments in legislation & guidance
Skelmorie (5 dead)
& Dolgarrog (16
dead) in 1925
1930: Reservoirs (Safety Provisions) Act –
periodic inspection by a qualified engineer
became mandatory
Major slips at 3
dams during 1937
due to high pore
pressures caused
by faster
construction rates
1937: Soil mechanics used in designs for the
first time
1940s: Berms added to designs to stabilise
slopes
1955: Drainage blankets & instrumentation
included in designs to control construction
pore pressure
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• Since 1925, no loss of life due to dam disasters in the UK
• However, dams have breached & many recent ‘near misses’
• Average age of dams in the UK is 115 years
• How will weather extremes impact potential failure modes of the UK’s ageing stock of reservoirs?
Recent ‘near misses’ & dam incidents
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Recent dam failure with no loss of life
Warmwithens dam
failure in 1970
The causes: Internal
erosion along the line
of a new tunnel
Lessons learnt:
Tunnelling works
through embankment
dams need to be
carefully designed in
terms of understanding
changes to stresses &
stability.
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Dam failures Developments in legislation &
guidance
Incidents at Lluest Wen
in 1969 and
Warmwithens in 1970
1975: Reservoirs Act 1975
1978: Publication of “Floods and
Reservoirs Safety”
Construction failure of
Carsington dam in 1984
1986: Reservoirs Act 1975 implemented
– New roles for enforcement,
supervision & ‘undertakers’
1990s: Publication of further guidance
on embankment dams
Links to UK dam safety legislation & guidance
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Recent ‘near misses’ & dam incidents
Ulley dam spillway failure in 2007
The causes: Masonry blocks plucked out due to turbulence.
Overtopping of the spillway walls.
Lessons learnt:
Spillway designs to
ensure sufficient
capacity so flows are
discharged safely
away from the dam
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Dam failures Developments in legislation & guidance
Failure of stepped
masonry spillway at
Boltby dam in 2005
and Ulley in 2007
2007: Post-incident reporting system
established
2008: The Pitt Report
2010: Floods and Water Management Act
2010: Guide on design of masonry
stepped spillways
Links to UK dam safety legislation & guidance
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Recent ‘near misses’ & dam incidents Rhymney Bridge spillway failure
Erosion
beneath
the slabs
Plucking of
bricks as water
flows at high
velocity
Uplift
pressure
forces 6t
slabs to
fracture
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Repairs commenced immediately in difficult weather conditions
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24hr working using rapid set concrete
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High volume pumps to assist with emergency draw down
Careful management of the res levels to avoid rapid draw down
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Preparations made for an auxiliary spillway as a precaution
CCTV patched to Gold Command where all decisions were made
Spillway half complete when an extreme storm event was forecast
Reservoir rose 13m in 8 hours due to snow thaw and rainfall
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Dam overflowed at 04.00 in dreadful weather conditions
All contingencies in place - sandbags stockpiled, staff & excavators at the ready
LRFs notified
Evacuation plans ready
Gold Command ready
……
The repairs held
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Before After
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Located 75 miles north of Sacramento; completed in 1968
At 235 m high, it is the tallest dam in the U.S.
Oroville dam spillway failure
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Early to mid-Jan: series of storms; main spillway gates opened
7th Feb: flows increase; spillway damage discovered; flows stopped
Timeline of events
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5
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8th to 10th Feb: reservoir continues to fill
11th to 12th Feb: emergency spillway overflows – the hillside began eroding uphill, threatening to collapse the concrete lip, causing the top 10m of the reservoir to empty
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12th Feb: main spillway gates opened again to reduce flows over the emergency spillway & evacuation commenced
13th Feb: crews fill eroded hillside with concrete & rocks
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13th to 26th Feb: main spillway flows continue erosion
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27th Feb: with the reservoir lowered, flows stopped down the main spillway to allow assessment of damage
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28th Feb: works commence to clear the debris at the base of the
main spillway.
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• The 180,000 evacuees have returned home
• Crews continue to place millions of tons of rocks and concrete in the emergency spillway
• Crews have cleared debris out of the river channel below the main spillway
• The Hyatt Power Plant has reopened
• In the coming months, crews will begin to fix the main spillway
• So far an estimated $200 million has been spent
Current state of play
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Cavitation:
If defects were present in the concrete spillway, water flowing over these may have created turbulence that formed bubbles that collapsed with powerful force, breaking apart the concrete
Uplift pressures:
Hydraulic uplift pressure (due to water below the spillway) may have built up, lifting the slabs
Theories on the causes of the Oroville dam spillway failure
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Internal erosion:
Sealant between the concrete slabs may have deteriorated, allowing water to seep underneath the spillway
The water then may have eroded the soil underneath the spillway
The slabs may have then collapsed into the voids
Or a combination of these causes?
Theories on the causes of the Oroville dam spillway failure
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• Ongoing and timely maintenance and monitoring of spillway channels
• Replacement of deteriorating joint sealant between slabs
• Ensure pressure relief drainage is functioning
• Maintenance of underdrains
• Consider undertaking NDT to check for voids underneath spillways
• Consider employing leakage detection techniques to check for any flow paths underneath spillways
Lessons learnt
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I’d like to thank Welsh Water for their permission to share the learning from the spillway incident at Rhymney Bridge, and acknowledge their commitment and management of the incident that led to a successful conclusion.
Acknowledgements
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56 ANY QUESTIONS?