1WMO: Climate and Water Department www.apfm.info
WMO
Training Workshop on Integrated Flood Management for the Nile Basin Countries
Effects and limits of traditional flood management options in light of future challenges
23-27 November 2009-09-16 Nairobi, Kenya
Armin Petrascheckformer member of
Federal Office for Environment
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Content1. Changing world and changing
society2. Problems and objectives of
traditional flood management3. Possibilities of intervention4. Discussion of structural measures5. Summary
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Traditional Flood ManagementTradition is something positive, since it is related to old values and
has often proofed effective during centuries.
Modern techniques are not necessarily positive just because they are recently developed
Its not the question if a method is modern or old
it is the question if the method is adequate or inadequate to solve the problem
Problems are changing
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We are living in a changing world
Change of temperature in Switzerland (observed)
Climate changes and with the climate the floods
Very high damage
High damage
Important floods in Switzerland
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Changing climate is one problem, but more important are demographic and social changes
Population of Egypt
3 619
3750
73
0
20
40
60
80
1750 1800 1850 1900 1950 2000 2050M
io. o
f inh
abita
nts
The resources remain the same, but demand increases
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Changes in social structures Urbanization
• Mega-cities and urban aglomerations– Economic growth driver’s– Loss driver’s– Vulnerability hotspots
• Root causes of Urbanization are not adressed through flood management
• Disparity of investment between Urban Development & flood management infrastructure in the entire catchment
• Sustainability of urban growth
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What is the result of the traditional flood management in a changing world
Dramatically increasing damages
We need a change
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Main aspect of traditional flood management is flood control by structural measures
Objectives:• Flood control: is a myth - possible only for a limited
range of floods• impend flooding: separates flood plain and river
neglects needs of the river (nature)• minimize damages: possible for existing land use
future development must be controlled by other means
These are reactive objectives
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The objective is not to avoid losses
You can loose only if you have.
The driving force of human activity is to generate benefits.
Everybody must earn enough to survive today, before he cares about tomorrow
Tolerable losses are a constraint but not a goal .Thus flood management must be embedded in the overall
economy (IFM)
Examples:• Rio Paraguay
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Jan T.L. Yap
–Ad-hoc and stand alone
–Reactive rather than proactive– Wrongly defined objective–Emphasis on structural measures thus shortfall of environmental aspects
–Monodisciplinary
–Lessons from past failure not learnt
Problems of traditional flood control
Traditional flood control is a part of integrated flood management (IFM) but insufficient for planning the future
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Mountainous areaRunoff controlSediment control
River corridorRegulating flowRetaining waterFlashing flowFloodplain
Retaining waterDiverting water
Traditional flood management measuresWhatever strategy is selected one has to understand the floods and the
damages
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Chain of effects
Damageg
Risk of damage
Emergencyplanning
Vulnerability
Risk of inundation
Hydrologic hazard
Meteorology
Catchmentarea
Riverbed
Damage is not directly dependent from rainfall. Several conditions mustbe fulfilled, before damage occurs.
Generation of flood damages
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Influencing damage
Damage
gRisk of damage
Emergencyplanning
Vulnerability
Risk of inundation
Hydrologic hazard
Meteorology
Catchmentarea
Riverbed
Retention in the areaForestation, Retention basins, Increase of infiltration,...
Structural protection measuresIncrease of river bed capacity, Dikes, Sills, Bank protection, ….
Appropriate land useRetention areas, Protection of single structures,….
Emergencymeasures Forecast, Rescue, Temporary measures
Flood protection measuresFlood plain management
Definition of intervention possibilities
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Dam
Additional aspects-Multi purpose utility
Issues-Deterioration of environment-Longitudinal disconnection -Capturing sediment-Possibility of dam failure-Confined geographic area-Unpopularity-Complexity of land acquisition -Social issues of resettlement
Functions-Attenuating flood peak-Generating hydro power-Regulating flow-Storing water
H
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Retention Pond
Additional aspects-Diverting flood damage torural / agricultural area-Efficient use of limited plain-Artificial wetlands (habitatand recreation)
Issues-Compensation for inundation-Uncertainty of efficiency
Functions-Attenuating flood peak duringflood events
H
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Embankment
Additional aspects-Can be combined with transport infrastructure or civil Defence infrastructure (shelters)
Issues-Lateral disconnection (water,sediment, aquatic species…)-Increase of flood damagepotential- »Design for failure »-Maintenance intensive
Functions-Blocking inflow to floodplain
E
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Functions-Reducing bank erosion-Sediment control-Flow concentration (navigation)
Groyne
Issues-In case unpopular due to aesthetic aspects
E
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Watergate
Functions-Preventing backwater frommain stream to tributary
Issues-Increase risk of inundationon the tributary
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High Standard Levee
Functions-Decrease of possibility offailure-multipurpose land use
Issues-Difficulty in securing space for levee (negotiation, cost)
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Diversion channel
Sea
Issues-High cost due to creatingnew channel (land acquisition)-Technical difficulty-Impact on environment-Full controll structure required on inflow to manage environmental flows/low flows
Function-Diverting river flow from main stream(reducing risk in urban area)
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Underground channel
Additional aspects-Less issues of land acquisition-possibility of multipurpose use
Issues-High cost -Technology requirements
Functions-Storing water-Diverting water
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Channelization
Issues-Deterioration of environment-Increase flow velocity (increase riskto downstream)
Functions-Regulating water flow-Reducing space requirements of natural water course
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Functions-Increase/maintainconveyance capacity
Channel maintenance
Issues-Deterioration of environment inriverbed-Natural recovery of sedimentcontinued maintenance Requirements-Effectiveness depends on theshape of the flood hydrograph-Sediment disposal/polution
H
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Sabo dam
Issues- Longitudinal disconnection-Deterioration of landscape-Maintenance and continued function
Functions-Blocking mud flow-Sediment control
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Summary• Traditional flood control tries to separate
human activity and floods instead of integrating them.
• Minimizing damages is only a partial objective.
• The driving force of human activity is to generate net benefits.
• Structural measures will remain an important tool in IFM
Discussion of IFM and its measures will follow later
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Changes leading to IFM• From defensive to pro-active approaches;• From Ad-hoc to Integrated Flood
Management (IFM);• Towards a culture of prevention by
managing flood risk & living with floods;• Balancing flood risk and achieving
sustainable development needs;• Change in decision making processes to
include risk management approaches.
International Seminar on River & Development
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Where are we going?IFM should lead to a brighter future
Thank you for your attention