Design, construction and

management of flood defences

Sun Dongya

Doctor, Senior engineer of professor level

China Institute of Water Resources and

Hydropower Research (IWHR), sundy@iwhr.com

International Training Programme 2010

Management of Flood Control and Disaster Mitigation

CONTENTS

1. Design philosophy for flood defence systems

2. Flood defence

3. Mechanism of dike failure

4. Dike design procedures

5. Dike construction

6. Filter and drain design

7. Structures through dikes

8. Dike risk management

9. Dike planning and ecological conservation

10. Conclusive remarks

1. Design philosophy for a flood

defence system

Flooding is one of

the main causes of

loss of life and loss

of property and

income in the world

and thus a major

drain on welfare of

people and an

important cause of

poverty.

http://big5.eastday.com:82/gate/big5/world.eastday.com/eastday/node81844/node81849/node118315/userobject1ai1858125.html

Hurricane

Katrina on

August 29,

2005

Damage estimates at the time of this writing are on the order of $100

to $200 billion in the greater New Orleans area

The official death count in New Orleans and southern Louisiana at the

time stands at 1,293, with an additional 306 deaths in nearby southern

Mississippi.

An additional approximately 300 people are still listed as “missing”

Flooding scenario

The two main items in flood management

Designing and construction a flood defence

system (physical infrastructure)

Designing and building a flood management

system (organization, information and tools)

Basic concept for flood prevention

Dike planning and construction

dike strengthening/raising

Temporary (flexible) measures

Free flood plains (occupation of detention areas)

Room (space) for rivers

Dredging

Storage basins

Etc.

Basic concept for flood prevention

Disaster Managements/Warning system and

Action plans

High Water Information/Management System

(HIS)

Measuring/monitoring network and

instrumentation

Evacuation plans

Relocation plans for endangered areas

Flood defence system

Dike (height, stability)

Polder (spatial planning, local measures)

River bed (widening floodplain, reducing resistance, deepening channels, etc)

River system (reforestation, retention+nature, storage reservoirs, flooding sequence)

Flood management system

Observations (rainfall, run off, discharges)

Prediction (short term, long term, models)

Communication (all kinds)

Decision (operation storage, retention, flood sequence, evacuation, emergency measures)

Implementation

Evaluation

Five systems have to interact:

Natural system

Infrastructure, dikes, dams, etc,

Observation & communication system

Professional system

Users & beneficiaries

2. Flood defence

Definitions

Flood defence: an embankment, wall, fill, piling,pump, gate, floodbox, pipe, sluice, culvert, canal,ditch, drain or any other thing that is constructed,assembled or installed to prevent the flooding ofland;

Dike: an embankment whose primary purpose is tofurnish flood protection from seasonal high waterand which is therefore subject to water loading forperiods of only a few days or weeks a year.

Sluice:

Dams/Reservoirs

Dike types according to use

Type Definition

Mainline and

tributary

dikes

dikes that lie along a mainstream and its

tributaries, respectively.

Ring dikes dikes that completely encircle or “ring” an area

subject to inundation from all directions.

Setback

dikes

dikes that are built landward of existing dikes,

usually because the existing dikes have suffered

distress or are in some way being endangered, as

by river migration.

Type Definition

Subdikes dikes built for the purpose of underseepage control.

Subdikes encircle areas behind the main dike which

are subject, during high-water stages, to high uplift

pressures and possibly the development of sand boils.

They normally tie into the main dike, thus providing a

basin that can be flooded during high-water stages,

thereby counterbalancing excess head beneath the top

stratum within the basin. Subdikes are rarely employed

as the use of relief wells or seepage berms make them

unnecessary except in emergencies.

Spur dikes Dikes that project from the maindike and serve to

protect the main dike from the erosive action of

stream currents. Spur dikes are not true dikes but

training dikes

Spur dike

Sea wall

Types of flood defences according to geometry

Dike design requirements

High enough

Watertight

Stable

Resistant against

erosion

Accessible

Functional elements Underground (1)

Dike core + Crest (2)

Watertight protection (3)

Revetment (4)

Stability berm (5)

Wave run up berm (6)

Drainage (7)

Seepage ditch (8)

Road for

inspection/maintenance (9)

1

23

4

56 7 8

94

Rock riprap erosion

protection

Grass revetment

3. Mechanism of dike failure

1 - Overflowing

2 - Wave overtopping

3 - Sliding inner slope

4 - Sliding outer slope

5 – Seepage-Piping

6 – Seepage-Uplift

7 - Settlement

8 - Erosion inner slope

9 - Erosion outer slope

10 - Erosion foreland

11 - Liquefaction

12 - Animals

Overflow / wave overtopping

Sand boil

Dike slope slippage

Failure of the toe of the channel

lead to collapse of the

revetment

Overtopping and erosion of

bank material led to the breach

of a river embankment

Overtopping Overtopping is not allowed

Forces: Driving force = high water level

and due to waves

Resistance force = Erosion

strength of grass / revetment

Calculation methods: Wave run up (z2%) or

overtopping (q)

Design figures for strength of

grass

Leakage and seepage

Leakage

Phreatic line (dike)

Stability inner slope

Seepage

Piezometric head

(aquifer)

Piping

Uplifting

landsideRiver side

Aquifer

Ditch

Piping Only occurs after uplifting

Forces:

Driving force =

flow in the pipe due to

flow in the aquifer

Resistance force =

equilibrium of sand

particles

Calculation methods:

Bligh or Lane criteria

Aquifer

River landside

sandboilH

L

Dike stabilization for seepage control

Relief wells

Seepage berm

Impervious;

Semipervious;

Pervious berms

Barron (1984) suggested that short berms

can be used where boiling is allowed at some

distance from the dike toe.

Statistics of Risks in Yangtze River Main Dike during the ’98 Flood

During the ’98 Flood, severe risks caused by embankment foundation piping

accounted for about 52.4%, which ranked the first among all those severe

risks occurred in the Yangtze River dikes. There were 7 dike breaches

occurred, and 5 breaches are caused by embankment foundation piping. In

the history, dike breaches are caused by piping accounted for 90%.

Types of

risksPiping

Riverbank

collapseLeakage Crack Drop Sloughing

Wave

erosion

Culvert

gateOthers total

Number of

Occurrence2025 330 2763 2795 106 615 316 220 235 9405

Percentage 21.5% 3.5% 29.4% 29.7% 1.1% 6.5% 3.4% 2.3% 2.5% 100%

Number of

severe

Occurrence

366 56 40 130 6 56 9 20 15 698

Percentage 52.4% 8.0% 5.7% 18.6% 0.9% 8.0% 1.3% 2.9% 2.1% 100%

H

s

hiy ii>icy

ii= hi/si

(a)

H

ix>icx

L1

(b)

H

A

L

(c)

图 4-2-3

C

H

s

hiy ii>icy

ii= hi/si

(a)

H

ix>icx

L1

(b)

H

A

L

(c)

图 4-2-3

C

H

s

hiy ii>icy

ii= hi/si

(a)

H

ix>icx

L1

(b)

H

A

L

(c)

图 4-2-3

C

8.05.0 cyi

07.0cxi

Silty sand

15.0cxiCoarse sand

L

A

BPiping channelPervious substrate

dike

Problems in countermeasures

Piping occurs near or far away from the toe. Because the piping

mechanisms are not well understood, emergency measures are taken

wherever piping occurred. They cost plenty of manpower and

materials to check the possible piping occurrences and to fight

against them. The critical distance between piping position and dike

toe need to be studied, beyond which dike safety will not be

threatened.

Aquifer

River landside

pipingH

L

River landside

piping

H

L

Aquifer

Seepage berms are usually adopted to be general

countermeasures. In some cases, according to the existing design

criterion of China, the calculated widths of landside seepage berms

are too large to be adopted in dike stabilization design.

Dike stabilization measures for piping prevention and

corresponding design criteria need to be investigated and modified

for abnormal dike foundation and based on state-of-art concept for

dike piping.

7

Necessary ?

berm

soil sand Gravel

Single-stratum dike foundation Two-stratum dike foundation

Dike bodyDike body

Three stratum dike foundation

Dike body

Multi-stratum dike foundation

Dike body

Complex and multiform dike foundation in China

februari 2000 45

Stability inner (outer) slope Forces:

Driving moment = wet earth

body

Resistant moment = shear

stresses

Special attention: uplifting

Calculation methods:

Rigid limit equilibrium

(Bishop)

Finite Element Method

Slip circle

Aquifer

River Polder

Non-circular slip surfaceSoft substrate

Erosion of the inner slope Forces:

Driving force = leakage

due to flow in the dike

Resistance force =

equilibrium of sand

particles

Calculation methods:

Design figures (analytical)

F.E.M Groundwater flow

calculation

Erosion outer slope Forces:

Driving force =

currents or water waves

Resistance force = erosion

strength (grass) or

equilibrium (revetment)

Calculation methods:

several

Rip rap formula’s (Hs/^D;

Pilarczyk / van der Meer).

Analytical model: Anamos.

4. Dike design procedures

(1) Conduct geological study based on a thorough

review of available data including analysis of aerial

photographs. Initiate preliminary subsurface explorations.

(2) Analyze preliminary exploration data and from this

analysis establish preliminary soil profiles, borrow

locations, and embankment sections;

(3) Initiate final exploration to provide:

a. Additional information on soil profiles.

b. Undisturbed strengths of foundation materials.

c. More detailed information on borrow areas and

other required excavations.

(4) Using the information obtained in Step (3):

a. Determine both embankment and foundation soil

parameters and refine preliminary sections where

needed, noting all possible problem areas.

b. Compute rough quantities of suitable material and

refine borrow area locations.

(5) Divide the entire dike into reaches of similar

foundation conditions, embankment height, and fill

material and assign a typical trial section to each reach.

(6) Analyze each trial section as needed for:

a. Underseepage and through seepage.

b. Slope stability.

b. Settlement.

d. Trafficability of the dike surface.

(7) Design special treatment to preclude any

problems as determined from Step (6).

Determine surfacing requirements for the

dike based on its expected future use.

(8) Based on the results of Step (7), establish

final sections for each reach.

(9) Compute final quantities needed;

determine final borrow area locations.

(10) Design embankment slope protection or

revetment.

d

V

Wave run-up Rp

Wind setup e

Safety surplus

Design flood level

Rock blockfilter

The determination of dike crest elevation

d

V

RK K K

mHLp

V p

1 2

0.5-0.3surplusSafety

0.5m-0.3surplusSafety 2

cosKV F

egd

Dike Geometry

1:21:3 1:21:3 1:21:3 1:21:3

（a） Clay dike （b） Sand dike

（d） Central clay core(c) Inclined clay core

1:21:31:21:3

1:21:3

1:21:3

Cutoff wall for seepage control

1:3

1:31:21:3

H>6m

Berm

L

A

BPiping channelPermeable substrate

dike

Dike Geometry

粉细砂

粉质粘土

粘土

砂壤土

粉质壤土

28.89

150 500

保护装置

W1-238.66

设计洪水位 43.38

35.00P1-333.44

P1-2

44.89

W1-139.07

33.44P1-1

P1-434.74

荆南长江干堤监测断面 (712+400)

38.66W1-3

700 750

200

细砂

粘土

31.40SL1-1

27.43

水泥土截渗墙

33.44

29.69

33.44P1-5

200

P1-7

P1-6

W1-439.37

W1-539.37

36.78W1-6

33.41P1-8

33.51

P1-1029.23

P1-9

设计洪水位

750

荆南长江干堤监测断面 (712+200)

1500

43.38 43.50

保护装置 管盖 45.18

550150

950

砂壤土

细砂

粉质粘土

水泥土截渗墙

2500 3000

40001500

保护装置

砂壤土

砂壤土

粉细砂

粉质粘土

粘土

粉细砂

砾卵石夹砂

砂壤土

荆南长江干堤监测断面 (705+383)

3000

W2-3

35.50

600

45.18

38.01W2-1

38.01W2-2 37.51

电缆

650

34.2234.87

P2-4P2-3P2-133.50

28.50

P2-2

保护装置 管盖

512150

43.25设计洪水位

200水泥土截渗墙

4000

32.83

150

管盖保护装置

W3-536.43

33.60P3-6

35.58P3-5

45.08

W3-438.74

36.08P3-4

水泥土截渗墙

荆南长江干堤监测断面 (687+794)

35.20W3-6 砂壤土

粉质壤土

粉质壤土

粉质壤土粉细砂

设计洪水位 42.92

200

粉质壤土

粉细砂

砂壤土

水泥土截渗墙

37.82W3-1

SL3-127.19

36.40

34.91P3-1

200

P3-236.40

W3-236.49

37.75W3-3

P3-334.95

粉质粘土

设计洪水位 42.76

荆南长江干堤监测断面 (685+786)

41.99

保护装置 44.17管盖

150500 568 597 25001050

保护装置

保护装置

500 628 583 3700

设计洪水位 42.92

荆南长江干堤监测断面 (680+300)

34.70水泥土截渗墙

600

43.82保护装置

P3-735.80

200

观测房

150

39.07

35.80P3-8

W3-7 38.57W3-8

管盖

P3-932.75

38.37W3-9

600 800 910

粉质壤土砂壤土

砂壤土

粘土

Cutoff across the whole pervious stratum

Dike Geometry-drainage system

Dike

enlargements

5. Dike construction

Dikes have been built by methods of compaction

varying from none to carefully controlled compaction.

In areas of high property values, high land use, and

good foundation conditions, dikes have been built

with relatively steep slopes using controlled

compaction,

In areas of lower property values, poor foundations,

or high rainfall during the construction season,

uncompacted or semicompacted dikes with flatter

slopes are more typical.

Vibratory roller

Sheepsfoot roller

Fill Placement/Compaction

Soils containing fines can be compacted to a specificmaximum dry density with a given amount of energy;however, maximum density can be achieved only at aunique water content called the optimum water content.Maximum dry density and optimum water content aredetermined in the laboratory by carrying out Proctortesting on collected samples.

Compactive effort can be increased by increasing contactpressure of the roller on the soil, increasing the number ofpasses, or decreasing the lift thickness. Combinations ofthese procedures to increase and control compaction on ajob will depend on difficulty of compaction, degree ofcompaction required, and economic factors.

Major textural classes:

gravel (>2 mm);

sand (0.12 mm);

silt (0.010.1 mm);

clay (<0.01mm);

Pervious materials, less than about 10% fines,

are commonly placed in 300 mm loose lift

thicknesses and compacted with four to five

passes of a vibratory steel-wheel rollers in

the weight range of 5 to 15 tons, or an

approved alternative.

Commonly, the specification calls for a

minimum 94% of the Standard Proctor

Maximum Dry Density for cohesive soil.

Compaction control

Non-cohesive soil: relative density Dr

0.6 0.65 depending on dike grade.

Cohesive soil: Compaction degree.

0.90.94 depending on dike grade.

%100minmax

max

ee

eeDr

%100max

d

dcD

Chinese dike construction criteria

6. Filter and drain design

Definitions

Base soil—The soil immediately adjacent to

a filter or drainage zone through which water

may pass. This movement of water may have

a potential for moving particles from the base

soil into or through the filter or drain materials;

Gradation curve (grain-size distribution)—

Plot of the distribution of particle sizes in a

base soil or granular material used for filters

or drains.

Definitions

Drain—A designed pervious zone, layer, or

other feature used to reduce seepage

pressures and carry water.

Filter—Sand or sand and gravel or

geotextiles designed to prevent movement of

soil particles from a base soil by flowing

water.

Basic purpose of filters and drains

To intercept water flowing through cracks or openings ina base soil and block the movement of eroding soilparticles into the filter. Soil particles are caught at thefilter face, reducing the flow of water through cracks oropenings and preventing further erosion andenlargement of the cracks or openings.

To intercept water flowing through the pores of the basesoil, allowing passage of the water while preventingmovement of base soil particles. Without filters, piping ofsusceptible base soils can occur when seepagegradients or pressures are high enough to produceerosive discharge velocities in the base soil. The filterzone is generally placed upstream of the discharge pointwhere sufficient confinement prevents uplift or blow-outof the filter.

Drains consist of sand, gravel, or a sand and gravel

Mixture, placed in embankments, foundations, and

backfill of hydraulic structures, or in other locations

to reduce seepage pressure.

A drain’s most important design feature is its

capacity to collect and carry water to a safe outlet at

a low gradient or without pressure build-up. Drains

are often used downstream of or in addition to a

filter to provide outlet capacity.

To minimize segregation and related effects, filters should have relatively uniform

grain-size distribution curves, without ―gap-grading‖ – sharp breaks in curvature

indicating absence of certain particle sizes. This may require setting limits that

reduce the broadness of filters within the maximum and minimum values

determined. Sand filters with D less than about 20 mm 90 generally do not need

limitations on filter broadness to prevent segregation.

7. Structures through dikes

Seepage reduction around pipes

and culverts

Seepage tends to creep along the relatively smooth surface of

pipes, culverts and floodboxes placed within the dike fill. There

are a few effective methods for reducing this seepage.

Seepage collars or cutoff walls have been historically used. The

difference between these devices is that a number of seepage

collars are typically used along a pipe, while typically only one

cutoff wall is used along a pipe or other structure.

Failure of embankment with anti-seep collars on concrete pipe

conduit

Failure of embankment with anti-seep collars on corrugated

metal pipe conduit.

8. Dike risk management

Routine Inspection: Verifies proper operation & maintenance activities conducted by the public sponsor.

Periodic Inspection: Verifies proper operation and maintenance and evaluates structure’s operational adequacy, structural stability and identifies components and features that the sponsor needs to monitor over time.

Periodic Assessment: Combination of PI and potential failure mode and consequences analysis used for initial screening and prioritization of RA.

Risk Assessment: Process of identifying the likelihood and consequences of dike failure to provide the basis for informed decisions on a course of action.

Dike Inspection Program

Dike Safety Action Classification

Consequences

Relative Annualized Loss of Life

Relative Economic Damage

Others, environmental, etc

Component Risk – What is driving risk

Information on data quality and gaps

Issues that influence certification

Documentation of confirmed failure modes

Recommended risk management actions

Risk Assessment Outcomes

9. Dike planning and

ecological conservation

Stresses of hydraulic projects on fluvial ecology

Channelization: cause to form a channel;

"channelize a river"

Make river channel straight

Use revetment with impermeable materials

Ecological conservation

Construction of dikes will generally lead tothe implementation of mitigation works, suchas plantings or habitat features, in order tooffset disturbance of existing habitats orvegetation.

The mitigation requirements for a projectgenerally will require extensive consultationin the design phase of the project prior tosettling upon a final alignment andconfiguration.

Ecological conservation

Floodplain areas have meandering streams and

marsh habitat. The streamside vegetation and the

aquatic insects that breed and reproduce in the

wetland habitat along the stream banks contribute to

the food chain.

The trees and the riparian vegetation along the

banks provide the shade to keep the water cool

during the summer and regulate the water

temperature during the winter. Therefore, most

floodplain areas are fisheries sensitive zones.

Ecological conservation

Construction of a diking project may alter the

natural habitat and have significant

detrimental effects on the fish habitat.

Careful planning and implementing of habitat

mitigation, compensation and environmental

enhancement measures, within or locally

outside the proposed flood protection area,

may achieve both flood protection and

environmental protection objectives.

Dike alignment

River channel pattern

Space for the rivers

Floodplain conservation

Meandering

Recovering the meandering of

river channel

Dike setback

Flood detention area

Cross Section of river channel

Diverse morphology

Flood diversion channel

Habitat enhancement

Lesso

ns fo

r

Histo

rical p

roje

cts

Riverbank protection

Riverbank protection is a very important part

of overall river stabilization to protect life and

property

Shrub vegetation structure is very important

for ecological conservation

Zone of compaction

Surface cover layer: 8085%

For stability

For vegetation

compaction

9094％

8085%

Dike compaction

Porous and permeable materials

Filter and cushion layer for erosion control

crushed stone

geotextile

Geotextile

Porous and permeable revetment

10--15cm厚

用土回填击实、

压实度80%左右

坡顶

原状土

（a）断面图 （b）俯视图

沟前沿

沟后沿

枝条交叉放置枝条伸入未扰动土

约15cm

约50--60cm

梢料层出露长度占总长的2/3--3/4

约40--90cm

夹角为10--30度

与竖直方向夹角为10--30度

备注： 1、

约25cm

2、施工次序由下而上，上层的开挖土作为下层的回填土

Removable dike

Appropriate dike crest elevation for sightseeing

Cultural symbols

Removable dike in urban areaCultural sculpture Too high to view the river

Landscape and sightseeing

10. Conclusive remarks

Future development

There is no “golden receipt” against floods

There is no “absolute safety” forever

Coping with Floods is an international problem

We have to joint the forces and exchange our experience.

Future development

Flood protection requires an integral approach in

which dike construction and reinforcement is just

one alternative.

Space for the rivers is essential in both controlling

the flooding problem and preventing

developments of the flood plains.

Measures can be taken aimed at the river, dikes

and damage reduction.

You are the right person to do it!

Believe in yourself. You know and understand the

situation better than anybody else.

Foreign expertises can only be advice, you have to do it

by yourself.