Post on 14-Oct-2020
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.
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”
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.