Historic dam failures and recent incidents - … · Historic dam failures and recent incidents . 2...

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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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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?