A Layman's Guide to Dams & Spillway (2011) - Presentation (44)

A LAYMAN’S GUIDE TO DAMS &

SPILLWAYS

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.

Wivenhoe Dam Brisbane River

Upper Reservoir Waterworks Reserve

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,

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

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.

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.

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.

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

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

ROCKFILL EMBANKMENT DAMS

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

CONCRETE FACED ROCKFILL DAMS

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

CFRD – Cross Section

3 – Concrete Plinth

4 – D/S Face Protection

5 – Compacted Rockfill Zone

6 – Transition Zones

7 – Upstream Face Membrane

Reece Dam

Upstream Face

<<< Slipform

<< Plinth

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

ROLLER COMPACTED CONCRETE GRAVITY DAMS

Meander Dam

Construction

H = 50m

Lc = 186m

Vc = 85,000m3

Vs = 24Mm3

Qs = 2600m3/s

MEANDER

RCC DAM

< D/S Face

RCC placing

<<< U/S Face

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

A - Gordon Dam start of Construction B - After Diversion Closure

CONCRETE ARCH DAMS

GORDON DAM

Concrete placement

at Block C

CONCRETE ARCH DAMS

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

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.

OUTLET WORKS

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

WARRAGAMBA DAM

Warragamba Dam

in the early 1960s.

H = 137m

Lc = 351m

Vc = 1.3Mm3

Vs = 2.1Gm3

WARRAGAMBA DAM – SPILLWAY UPGRADE - 2008

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

CAMARA DAM FAILURE - BRAZIL

This RCC Dam failed

on June 2004.

H = 50m

Lc = ?

Failure flood 17Mm3

5 Deaths

20 Vanished

250 Homes lost

800 Families

homeless

CAMARA DAM FAILURE - BRAZIL

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 CONSTRUCTION

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.

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,

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.

A Layman's Guide to Dams & Spillway (2011) - Presentation (44)

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