flood defence systems(97)

Kuala Lumpur, 10 – 14 August 2009

Flood Defence SystemsFlood Defence SystemsJan T.L. Yap - AguaJaringJan T.L. Yap - AguaJaring

Integrated Flood ManagementIntegrated Flood Management

Flood Embankment in Action

Flooded Flood Plain

Failed Flood Embankment

Piping through Embankment

Confined Seepage

Strengthening Flood Embankment

Good Performanced Embankment

Failed First-line Embankment

Emergency Intervention - Blow-up

Kuala Lumpur, 10 – 14 August 2009

Flood Defence SystemsFlood Defence Systems

Philosophy of Risk Management

Failure MechanismsFailure TreeProbabilistic Design

Overview design methods of embankments

• Initialy: pure based on experiences. Crest level established with reference to the highest known water level;

• In the 50s: applying statistical techniques to determine the “Design

Water Level” → Deterministic design method using fixed design values for the various parameters;

• Since the 70s – 80s: Probabilistic Design Method → using stochastic character of the various load and strength parameters →

based on an analysis of failure mechanism and their probabilities.

Review deterministic design methods

• Crest level only one of the design parameters of embankment profile. Slope, crest width & berms: stability, maintenance, construction and usage of crest;

• Hydraulic conditions & soil mechanics parameters essential for embankment stability → limited degree of accuracy → Safety factors applied based on experience, tradition and intuitive judgement;

• Only determined per embankment stretch or section, while it is in fact part of a flood defence system → many stretches of different characteristics, and many structures like sluices & water gates and …….. protecting different regions: number of inhabitants, invested capital, strategic utilities, future land use, etc.

Components of a flood defence system

Shortcomings deterministic design methods

• Various embankment sections in a defence system do not provide same degree of safety;

• It is not known which failure mechanism gives the greatest contribution to the probability of failure of an embankment section;

• The overall length of the embankment system has no influence upon the design of the embankment section;

• Magnitude of damage or loss has no influence on the design;

• The actual probability of inundation (flooding) of the protected area is not known

Principle of Risk Analysis

Risk = Probability x Consequence

• Probability of an undesirable event: explosion, inundation, etc.

• Consequence of the occurrence of that event: → economic loss, damage, loss of life, etc.

Risk Analysis: the whole set of activities asimed at

Quantifying

the probability of an undesirable event ..and .. the consequence of the occurrence of that event.

Advantages of Probabilistic Approaches

• The flood system is analysed and described as a whole;

• Components of the system can be better inter-related, i.e. less over- and under-designing;

• Various uncertainties are rationally incorporated in the assessment of the safety of the system;

• Better insight into the sensitivity of probability of failure of the system related to the various uncertainties;

• Better insight into the priority for improving the flood defence system (maintenance).

More …..

Failure tree analysis

Probability of Failure

Design Point

Kuala Lumpur, 10 – 14 August 2009

Flood Defence SystemsFlood Defence Systems

Reducing Flood Damages

Flood FightingFlood ProofingTemporary & Demountable Flood Defence Structures

Emergency Measures - Flood Fighting

Controling Under-seepage

Sand Migration due to Underseepage

Road System as Floodway

Temporary Flood Wall

Emergency Flood Wall

Emergency Flood Wall (2)

Local Flood Fighting

Flood Proofing to Reduce Damage

Columns for Emergency Flood Walls

Movable Flood Wall

Floating Houses

Floating Houses (2)

Kuala Lumpur, 10 – 14 August 2009

Thank you……Thank you……