A Layman's Guide to Dams & Spillway (2011) - Presentation (44)
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Transcript of A Layman's Guide to Dams & Spillway (2011) - Presentation (44)
A LAYMAN’S GUIDE TO DAMS &
SPILLWAYS
by
Bram Knoop & Bruce Cole
Australian Engineering Heritage 2011
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
Wivenhoe Dam Brisbane River
QLD
Australian Engineering Heritage 2011
Upper Reservoir Waterworks Reserve
Australian Engineering Heritage 2011
H = 18m
Lc= 204m
Vef= 0.135Mm3
Vs= 0.300Mm3
<< Spillway &
Bypass
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
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
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
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
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
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
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
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
ROCKFILL EMBANKMENT DAMS
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BLOWERING DAM
H = 112m
Lc = 808m
Vrf = 8.6Mm3
Qs =2350m3/s
Vs = 1,600Mm3
< Power Stn.
<< Tail Race
ROCKFILL EMBANKMENT DAMS
Blowering Dam Cross Section SMHA Diagram
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CONCRETE FACED ROCKFILL DAMS
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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
CONCRETE FACED ROCKFILL DAMS
CFRD – Cross Section
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3 – Concrete Plinth
4 – D/S Face Protection
5 – Compacted Rockfill Zone
6 – Transition Zones
7 – Upstream Face Membrane
CONCRETE FACED ROCKFILL DAMS
Reece Dam
Upstream Face
<<< Slipform
<< Plinth
<< Plinth
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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
ROLLER COMPACTED CONCRETE GRAVITY DAMS
Meander Dam
Construction
H = 50m
Lc = 186m
Vc = 85,000m3
Vs = 24Mm3
Qs = 2600m3/s
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ROLLER COMPACTED CONCRETE GRAVITY DAMS
MEANDER
RCC DAM
< D/S Face
RCC placing
<<< U/S Face
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ROLLER COMPACTED CONCRETE GRAVITY DAMS
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Meander Dam
Downstream face
as the dam nears
completion
This RCC Gravity
Dam has a central
stepped spillway
with a d/s impact
basin.
CONCRETE ARCH DAMS
Australian Engineering Heritage 2011
A - Gordon Dam start of Construction B - After Diversion Closure
CONCRETE ARCH DAMS
Australian Engineering Heritage 2011
GORDON DAM
<
Concrete placement
at Block C
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.
MULTIPLE ARCH & BUTTRESS DAMS
Australian Engineering Heritage 2011
Miena Multiple Arch Dam – Tas.
Julius Dam - Qld
Oberon Buttress Dam - Qld
UNUSUAL SPILLWAYS
Geehi Dam – Glory Hole Spillway
Crotty Dam - Chute Spillway on the crest
and downstream face of a rockfill dam.
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OUTLET WORKS
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Hume Dam Outlet Valves
Typical Cone Dispersion Valve
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
WARRAGAMBA DAM
Warragamba Dam
in the early 1960s.
H = 137m
Lc = 351m
Vc = 1.3Mm3
Vs = 2.1Gm3
WARRAGAMBA DAM – SPILLWAY UPGRADE - 2008
Australian Engineering Heritage 2011
H = 142m
Lc = 351m
Right Bank
Fuse Plug
Spillway
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
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
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.
DAM FAILURES
Malpasset Dam
< July 1959
And after 2-12-1959
Right & Left Banks
GORDON DAM
GORDON DAM
GORDON DAM
GORDON DAM CONSTRUCTION
Australian Engineering Heritage 2011
Left: After the
upstream coffer
dam was
breached.
Right: With the
storage level
rising.
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
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
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