a layman's guide to dams & spillway (2011) - presentation (44)
TRANSCRIPT
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A LAYMAN’S GUIDE TO DAMS &
SPILLWAYS
by
Bram Knoop & Bruce Cole
Australian Engineering Heritage 2011
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INTRODUCTION
Dams generally attract public attention:-
• When they are in the planning stage,
• During droughts, - water restrictions,
• During major floods, - inundation.
• And when they receive a Bronze Plaque.
Australian Engineering Heritage 2011
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Wivenhoe Dam Brisbane River
QLD
Australian Engineering Heritage 2011
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Upper Reservoir Waterworks Reserve
Australian Engineering Heritage 2011
H = 18m
Lc= 204m
Vef= 0.135Mm3
Vs= 0.300Mm3
<< Spillway &
Bypass
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OUTLINE
• Public Expectations
• Functions of Dams & Essential Features
• Spillway Requirements & Types
• ANCOLD Register of Large Dams & Types of Dams
• Examples of types of dams, Earthfill Embankments, etc.
• This will include spillways, and Outlet Works
• Dam Upgrades,
Australian Engineering Heritage 2011
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PUBLIC EXPECTATIONS
Typical questions included:
• Why can’t dams control large floods?
• Why do we have a ‘100 year flood’ 34 years
after the previous 100 year flood in 1974?
• Why can’t flood waters be diverted to the dry
inland Murray-Darling Basin?
Engineering Heritage Conference 2011
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FUNCTIONS OF DAMS
Mainly to store water for later use in:
– Irrigation farming– (#) ~70%
– Industrial use ~20%
– Domestic consumption <10%
– Flood protection
– Navigation
– Environmental flows
– Waste storages – tailings dams
– Recreational activities # - % storage capacity of all dams in Australia
Australian Engineering Heritage 2011
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ESSENTIAL FEATURES
Extensive studies are required to establish the feasibility of a major dam project.
This includes hydrological, engineering and economic evaluations.
• Dam Sites – normally on-stream, but can be or off-stream,
• Foundations – need to be stable and water tight,
• Structural Stability – requires appropriate safety factors,
• Spillway Facilities – can be un-controlled, or controlled,
• Outlet Works – gates, valves to suit specific requirements.
All parts need to be optimised to for an economic dam project.
Australian Engineering Heritage 2011
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SPILLWAY REQUIREMENTS
• To release excess water from the reservoir.
• Capacity: initially based on existing flood data, or experience.
• Now Based: on probable maximum precipitation (PMP),
• PMP estimates: depend geographic and atmospheric conditions,
• And on probable maximum flood (PMF) estimates, this is the notional
“upper limit” for a specific catchment area.
• The annual exceedance probability (AEP) for a PMF event may vary
from 1/10E7 for small catchments to 1/10E4 for large catchments.
There are different types of spillways some of which will be pointed out.
Australian Engineering Heritage 2011
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TYPES OF SPILLWAYS
• Uncontrolled Spillways – Free flow over a spillway crest.
• Controlled Spillways – Flow regulated by gates.
• Earthfill and Rockfill Embankments: normally have
Spillways adjacent to the dam embankment.
• Concrete Dams: can have Spillway Crests that are part of the
dam structure; or they can have a Spillway adjacent to the dam.
Australian Engineering Heritage 2011
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ANCOLD REGISTER OF LARGE DAMS
Types of Dams No. Examples Ht m
Earthfill Embankment 260 Eucumbene 116
Rockfill Embankment 145 Dartmouth 180
Concrete Gravity 108 Warragamba 142
Concrete Arch 40 Gordon 140
Concrete Buttress 5 Meadowbank 43
Multiple Arch Buttress 3 Julius 38
561
Australian Engineering Heritage 2011
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EARTHFILL EMBANKMENT DAMS
EUCUMBENE DAM
H = 116m
Lc = 579m
Vef = 6.75Mm3
Spillway >>>
Qs = 475m3/s
Vs = 4,800Mm3
This is the largest
Dam of its type.
SMHA Photo
Australian Engineering Heritage 2011
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ROCKFILL EMBANKMENT DAMS
Australian Engineering Heritage 2011
BLOWERING DAM
H = 112m
Lc = 808m
Vrf = 8.6Mm3
Qs =2350m3/s
Vs = 1,600Mm3
< Power Stn.
<< Tail Race
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ROCKFILL EMBANKMENT DAMS
Blowering Dam Cross Section SMHA Diagram
Australian Engineering Heritage 2011
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CONCRETE FACED ROCKFILL DAMS
Australian Engineering Heritage 2011
REECE DAM
Pieman River P. D.
This is the largest CFRD
in Australia
< Spillway
<<< Power Station
H = 122m
Lc = 374m
Vr = 2.7Mm3
Qs = 4714m3/s
Vs = 641Mm3
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CONCRETE FACED ROCKFILL DAMS
CFRD – Cross Section
Australian Engineering Heritage 2011
3 – Concrete Plinth
4 – D/S Face Protection
5 – Compacted Rockfill Zone
6 – Transition Zones
7 – Upstream Face Membrane
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CONCRETE FACED ROCKFILL DAMS
Reece Dam
Upstream Face
<<< Slipform
<< Plinth
<< Plinth
Australian Engineering Heritage 2011
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CONCRETE GRAVITY DAMS
GUTHEGA DAM
H = 34m
Lc = 139m
Vc = 44,000m3
<< Spillway
Qs = 1420m3/s
Vs = 1.8Mm3
< Spillway Apron
This was the first
Dam in the Snowy
Hydro Scheme
Australian Engineering Heritage 2011
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ROLLER COMPACTED CONCRETE GRAVITY DAMS
Meander Dam
Construction
H = 50m
Lc = 186m
Vc = 85,000m3
Vs = 24Mm3
Qs = 2600m3/s
Australian Engineering Heritage 2011
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ROLLER COMPACTED CONCRETE GRAVITY DAMS
MEANDER
RCC DAM
< D/S Face
RCC placing
<<< U/S Face
Australian Engineering Heritage 2011
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ROLLER COMPACTED CONCRETE GRAVITY DAMS
Australian Engineering Heritage 2011
Meander Dam
Downstream face
as the dam nears
completion
This RCC Gravity
Dam has a central
stepped spillway
with a d/s impact
basin.
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CONCRETE ARCH DAMS
Australian Engineering Heritage 2011
A - Gordon Dam start of Construction B - After Diversion Closure
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CONCRETE ARCH DAMS
Australian Engineering Heritage 2011
GORDON DAM
<
Concrete placement
at Block C
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CONCRETE ARCH DAMS
Australian Engineering Heritage 2011
GORDON DAM
This is the highest arch
dam and largest storage
in Australia
H = 140m
Lc = 198m
Vc = 154,000m3
Vs = 12,450Mm3
Qs = 175m3/s
This is via an
emergency spillway that
is made by removing
two crest parapet wall
sections.
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MULTIPLE ARCH & BUTTRESS DAMS
Australian Engineering Heritage 2011
Miena Multiple Arch Dam – Tas.
Julius Dam - Qld
Oberon Buttress Dam - Qld
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UNUSUAL SPILLWAYS
Geehi Dam – Glory Hole Spillway
Crotty Dam - Chute Spillway on the crest
and downstream face of a rockfill dam.
Australian Engineering Heritage 2011
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OUTLET WORKS
Australian Engineering Heritage 2011
Hume Dam Outlet Valves
Typical Cone Dispersion Valve
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DAM UPGRADES
• ANCOLD produced a number of Guidelines – including:
• Design of Dams for Earthquake – 1998a,
• Acceptable Flood Capacity – 2000a,
• Assessment of the Consequences of Dam Failure – 2000b,
• Guidelines on Risk Assessment – 2003.
• Older dams may have insufficient spillway capacity.
• Over the past 40 years many dams have been modified to
comply with currently accepted criteria for dam safety and
flood capacity
Australian Engineering Heritage 2011
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WARRAGAMBA DAM
Warragamba Dam
in the early 1960s.
H = 137m
Lc = 351m
Vc = 1.3Mm3
Vs = 2.1Gm3
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WARRAGAMBA DAM – SPILLWAY UPGRADE - 2008
Australian Engineering Heritage 2011
H = 142m
Lc = 351m
Right Bank
Fuse Plug
Spillway
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INCIDENTS & FAILURES
Dam Incident:
A structural failure that generally can be fixed, usually at great expense.
Examples range from: failed gate works, major leakages, substantial
settlements, concrete cracking, etc.
Dam Failure:
A structural failure that can not be fixed and is normally followed by a
judicial inquiry.
Recent Examples:
Camara Dam (RCC Dam) – Brazil – June 2004
Malpasset Dam (Arch Dam) – France – 2nd December 1959
Australian Engineering Heritage 2011
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CAMARA DAM FAILURE - BRAZIL
Australian Engineering Heritage 2011
This RCC Dam failed
on June 2004.
H = 50m
Lc = ?
Vc =?
Failure flood 17Mm3
5 Deaths
20 Vanished
250 Homes lost
800 Families
homeless
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CAMARA DAM FAILURE - BRAZIL
Australian Engineering Heritage 2011
This was a first filling failure.
The left bank section of the dam
section of the dam collapsed as
shown.
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DAM FAILURES
Malpasset Dam
< July 1959
And after 2-12-1959
Right & Left Banks
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GORDON DAM
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GORDON DAM
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GORDON DAM
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GORDON DAM CONSTRUCTION
Australian Engineering Heritage 2011
Left: After the
upstream coffer
dam was
breached.
Right: With the
storage level
rising.
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RECENT HISTORY
• Australia experienced below average
rainfalls for most of the decade 2000-2010
• Dam storage levels dropped to low levels
• Water restrictions applied in many towns
• This changed in 2010-2011 – when …..
• The eastern states saw extensive flooding
• With property damage and loss of life.
Australian Engineering Heritage 2011
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DAM PROJECT INVESTIGATIONS
Extensive Studies are required to Establish the Feasibility
of a Major Dam Project; these include:
• Catchment Surveys; geography, climate, hydrology, environment, geology,
• Water Resources; run-off, minimum, average, peak flows,
• Dam Site & Reservoir Investigations; soil, rock, stability, materials,
• Suitable Dam Design Types; embankment, concrete gravity, arch,
• Suitable Spillway Arrangements; uncontrolled, controlled,
• Appropriate Outlet Works; gates, valves,
• Economic Studies; project costs, operating costs, returns on investment,
Australian Engineering Heritage 2011
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PUBLIC INTEREST
• The 2011 floods in Queensland were widely reported.
• There appeared to be a lack of understanding of the principal features of large dams and their operation.
• This applied to journalist, and members of the public.
• A Commission of Inquiry was set up to investigate the Queensland Floods.
Australian Engineering Heritage 2011