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