Part B1: Basics
B1.2 Reservoirs
B1.2 Reservoirs
Topics
• Why store?
– Raise head, smooth flow, conflicts and trade offs
• Determination of reservoir volume/height
– Mass curve approach, simulation approach
• Dam design
– Forces on a dam, Types of dam, Seepage, Spillways
• Technical problems with dams
– Silting, failure
• Social impact of dams
– Seminars (Monday W6)
B1.2 Reservoirs
Seminars: Monday 17/1, 16:00
• Go to www.dams.org
– World commission on dams report overview (skim this
– it’s pretty long and dull – concentrate on the findings)
– Responses to the report
• Contrast donors (such as the ADB) with utilities (such as
the Indian Ministry of water resources) and dam-oriented
organisations (such as ICOLD or the ICE)
– Case studies (2)
• On the web (not necessarily on dams.org)
– Find an example of a “bad” dam project
– Find an example of a “good” dam project
• We will be discussing
– Who benefits and who loses when a dam is built?
– Who makes the decisions?
– What makes a dam good or bad?
B1.2 Reservoirs
Seminar groups
Group 1 (16:00) Group 2 (16:30)
Gunjan Dhingra
Mike Farrow
Hannah Jones
Matt Knight
Paul Knowles
Peter Adams
Elizabeth Aldridge
Jonathan Bailey
Khesraw Bashir
Christopher Baxter
Richard Buckland
Dafydd Caffery
Samuel Carter
Nedim Dzananovic
Philip Hallgarth
Neil Harding
Martin Hill
Karen Hockey
Ching Hong
Adam Ithier
Peter Jordan
Jan Jozefowski
Rob Morford
Chris Swinburn
Kate Taylor
Celia Way
Marie Wells
Matt Whitley
Eral Kahveci
Imra Karimn
Martin Kendrick
Shua Lii
Beth Mcdowall
Adil Munir
Roger Palmer
Anthony Pearson
Gareth Pilmoor
Ann Ruthven
Matthew Scott
Ben Sheterline
Melanie Sim
Nicholas Thompson
Daniel Tkotsch
Christopher Tompkins
Ian Yeung
B1.2.1 Reservoirs Why store
• Raise head
– Hydro power
– Allow greater flow to irrigation
• Smooth flow
– Reliable Hydro power
– Off season irrigation
– Flood control
– Domestic Water supply
• Other reasons
– Fishing
– Leisure
B1.2.1 Reservoirs Why store: Conflicts
• Maximising head vs. Maximising storage – If the storage is used, the head is reduced
• Water use vs. flood control – Water use prefers a full reservoir (for use later)
– Flood control the reservoir should be empty (so floodwater can fill it)
B1.2.1 Reservoirs Why store: The anatomy of a reservoir
B1.2.2 Reservoirs How much to store
3 2( ) ( )h f V f A= =
B1.2.2 Reservoirs How much to store
n in outQ Q Q= −
in stream precipitationQ Q Q= +
......out used spill evaporation leakage seapageQ Q Q Q Q Q= + + + + +
precipitationQ AP≈
B1.2.2 Reservoirs How much to store: Mass curve
B1.2.3 Reservoirs Dam design: Forces on a dam
2
2
hF
γ=
2
hF W tγ= +
W
γ is the specific weight of water
B1.2.3 Reservoirs Dam design: Types of dam
Type Materials Typical cross section
Plan view
Gravity Concrete, rubble masonry
Arch Concrete
Buttress Concrete, ferrocement, timber,
steel
Embankment Earth, rock
B1.2.3 Reservoirs Dam design: Seepage: Flow nets
• Lines of constant potential, and constant flow
– Perpendicular
– Should form a series of squares
• Note boundary conditions
• ES254 Geotechnics Lectures 8&9
B1.2.3 Reservoirs Dam design: Seepage: Typical flow nets
B1.2.3 Reservoirs Dam design: Seepage: Typical flow nets: Earth dams
B1.2.3 Reservoirs Dam design: Seepage: Zoned earth dams: piping
Toe drain
Blanket drain
Chimney and blanket drain
Impermeable core and blanket
B1.2.3 Reservoirs Dam design: Seepage: Earth dams
B1.2.3 Reservoirs Dam design: Seepage: Earth dams: Zoned
Filters
Core
B1.2.3 Reservoirs Dam design: Seepage: Zoned earth dams
B1.2.3 Reservoirs Dam design: Seepage: Zoned earth dams
Ramganga project
B1.2.3 Reservoirs Dam design: Seepage: Zoned earth dams
Kishan rockfill dam
B1.2.3 Reservoirs Dam design: Spillways: Types
Side channel
Chute
Shaft
Syphon
Ogee
B1.2.3 Reservoirs Dam design: Spillways: Side channel
B1.2.3 Reservoirs Dam design: Spillways: Chute spillways
B1.2.3 Reservoirs Dam design: Spillways: Shaft spillways
B1.2.3 Reservoirs Dam design: Spillways: Ogee spillways
B1.2.3 Reservoirs Dam design: Spillways: Ogee spillways
B1.2.3 Reservoirs Dam design: Spillways: Hydraulic jump
Hd
h1
h2
2
2
2
v
g
2
1
2
v
g
h
hL
B1.2.3 Reservoirs Dam design: Spillways: Hydraulic jump
V = Stream velocity (m s-1)
R = Hydraulic radius
S = Slope
n = Manning roughness
B1.2.3 Reservoirs Dam design: Spillways: Hydraulic jump Manning's equation
2 3 1 2R S
Vn
=
p = pressure (Pa)
ρ = Density (kg m-3)
g = Gravity (m s-2)
v = velocity (m s-1)
z = elevation (m)
B1.2.3 Reservoirs Dam design: Spillways: Hydraulic jump Bernoulli's equation
2
constant2
p vz
g gρ+ + =
B1.2.3 Reservoirs Dam design: Spillways: Hydraulic jump: Sums: Critical depth
E
h
2
2
vE h
g= +
crith
minE
Tranquil
Rapid
E = Specific
Energy (m)
h = head (m)
g = Gravity
(m s-2)
v = velocity
(m s-1)
B1.2.3 Reservoirs Dam design: Spillways: Hydraulic jump: Sums: Head loss
( )22
22
L d
vh H h h
g
= + − +
Hd
h1
h2
22
2
v
g
21
2
v
g
h
hL
Hd
h1
h2
22
2
v
g
21
2
v
g
h
hL
B1.2.3 Reservoirs Dam design: Spillways: Hydraulic jump: Sums: Height of the jump
1 22 2
1 1 1 12
2
2 4
h h v hh
g
= + +
B1.2.3 Reservoirs Dam design: Spillways: Hydraulic jump: Location of the hydraulic jump
B1.2.3 Reservoirs Dam design: Spillways: Encouraging a jump
B1.2.4 Reservoirs Technical problems with dams: Silting
B1.2.4 Reservoirs Technical problems with dams: Silting
B1.2.4 Reservoirs Technical problems with dams: Failure modes
• Overtopping – inadequate spillways (1/3)
• Foundation failure (1/3)
– Excess seepage through foundation
– Piping – insufficient drainage/grading
• Wave action
• Erosion of downstream face
• Slump
• Bank stability
• Seismic activity
• Degradation – lack of maintenance
• Material supplies sub specification
B1.2.4 Reservoirs Technical problems with dams: Failure: St Francis breach
B1.2.4 Reservoirs Technical problems with dams: Failure: St Francis breach
B1.2.4 Reservoirs Technical problems with dams: Failure: Piping - Hellhole dam
Dec 22 3:00 pm Dec 23 7:00 am
Dec 23 9:30 am Dec 23 3:30 pm
B1.2.4 Reservoirs Technical problems with dams: Failure: San Luis Dam Slide
B1.2.4 Reservoirs Technical problems with dams: Failure: Fatehgarh dam earthquake damage
B1.2.4 Reservoirs Technical problems with dams: Failure: Vaiont dam bank slip
B1.2.5 Reservoirs Social impact of dams
• Climate change
• Fertility of downstream banks
• Displacement
• Changes in local economy
• Deforestation
• Possibility of financial collapse
• Possibility of failure
• See; World commission on dams www.dams.org
B1.2 Reservoirs
Summary
• Storage needs may conflict
• Mass balance and the mass curve are useful ways
to size reservoirs
• Seepage is an issue with earth dams but can be dealt with by zoning
• There are several varieties of spillway, including side channel, chute, shaft, syphon, and ogee
• Hydraulic jump is a useful technique to reduce
spillwater levels
• Dams can fail by silting, overtopping, foundation
failure wave action, erosion and lack of maintenance
• Dams can have social and environmental impacts
B1.3 Next…..Water conveyance
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