Lecture 7 Flashcards
Concepts of the role of civil engineers in hazard reduction and mitigation
The internationally recognised definitions and concepts relating to hazards (such as earthquakes, landslides, floods, volcanic eruptions etc.) and their consequences, risk reduction and the disaster risk management cycle.
People and perspectives of the role of civil engineers in hazard reduction and mitigation
how approaches to disaster risk have changed over time; the perspectives and actions of disaster risk reduction policy-makers, practitioners, researchers and at-risk communities; and current risk reduction practices and policies.
science-into-practice of the role of civil engineers in hazard reduction and mitigation
selection of appropriate hazard and risk assessment models using criteria such as the scope and spatial scale of the project, the quality and quantity of data available, model complexity and outputs, and end-user requirements. Selection of risk reduction approaches for different hazards and different parts of the disaster risk management cycle (i.e. before, during, or after the disaster event).
UNISDR Prevention definition
activities to avoid existing and new disaster risks.
UNISDR Mitigation definition
The lessening or minimizing of the adverse impacts of a hazardous event.
UNISDR Preparedness definition
The knowledge and capacities developed by governments, response and recovery organisations, communities and individuals to effectively anticipate, respond to and recover from the impacts of likely, imminent or current disasters.
Risk identification
recognise and describe the risks (may be associated with a single hazard or multi-hazards) and the scope of the assessment.
Risk analysis
understand the nature and sources of the risk and estimate the level of risk (a quantitative or qualitative calculation of H, E, V and risk).
Risk evaluation
compare risk with risk criteria (acceptable, tolerable, unacceptable).
Typical methods for assessing failure
Analytical
Dynamic LEM
Analysis of Continua
Discrete Element Models
Typical methods for assessing rotational and translational slides
Analytical: Static Equilibrium analysis - wedge analysis, methods of slices
Dynamic LEM: Slope hydrology (or other dynamic processes) modelled over time and F calculated each time step
Analysis of Continua: Stress-strain analysis based on rheological equations (Discontinuous Deformation Analysis, DDA, allows detachment of failed mass)
Discrete Element Models: Movement of individual rigid elements, from grain scale to blocks of material.
Landslide mitigation: reducing exposure
Hazard hotspot identification and ranking
Combine with exposure and vulnerability assessment
Use for planning controls (‘zonation’)
Combine with early warning
Hazard reduction: Possible civil engineering measures
Site specific analysis. Reinforce, retain, drain, reduce driving forces. Observe design standards.
Mitigation: Possible civil engineering measures
Site-specific analysis. Debris catch fences and storage, runout diversion channels etc.
Wide area analysis and site specific checks. Land use planning controls, road network redundancy
Resistance of structures not usually considered an option
Preparedness: Possible civil engineering measures
National rainfall-triggering thresholds from empirical data, linked to weather forecasts.
Wide area analysis. Hotspot identification and planning for debris clearance (especially roads)
Types of Floods
River floods (fluvial) Surface water floods (pluvial) Groundwater floods Sewer floods Coastal floods
Flood defences and protection
barriers, embankments (temporary or permanent)
Conveyance
routing potential flood waters via natural or artificial channels (a function of channel cross section, slope and frictional resistance; and capacity is determined by cross section and friction): straightening channels; increasing bank heights; dredging; relief channels; culverts
Storage
attenuation of surface water runoff reduces peak flows within the channel: on-line and off-line attenuation and storage
Drainage systems, urban infiltration and permeability
without careful design, urban impermeable surfaces, storm drains and sewers increase rainfall runoff rates into rivers, and drain capacities can also be exceeded: SUDS
Groundwater management
part of the catchment water storage system and also used as a water supply: recharge vs extraction, protect from pollution, alternative water supplies
Structural measures for flood hazard reduction and mitigation
- Flood defences and protection
- Conveyance
- Storage
- Drainage systems, urban infiltration and permeability
- Groundwater management
- Wetlands and environmental buffers
- Building design, resilience and resistance
Dredging
clear the river bed by scooping out mud, weeds, and rubbish with a dredge
Primary volcanic hazards
lava and pyroclastic flows, tephra falls, gases
Secondary volcanic hazards
lahars, landslides, floods, tsunamis, tremors, atmospheric effects (ash clouds and air pollution)
Types of volcanic eruption
- Plinean: columns of gas and ash ejected; pumice falls and gas blasts
- Pelean: pyroclastic flows, lateral blasts and viscous lava flows giving steep sided cones
- Vulcanian: ash-laden gas explosions
- Strombolian: incandescent cinder, lapilli and lava bombs
- Icelandic: low viscosity, basaltic lava, parallel fissures, rift
- Hawaiian: low viscosity, fire fountains, fast flowing over long distances
Volcanic hazard mitigation
- Controlling lava flows: explosives, artificial barriers, water sprays (limited effectiveness)
- Controlling lahars and debris flows: Sediment traps, diversion barriers
- Resilient buildings: strengthening structures to withstand tremors and debris impacts, doors and window shutters to resist hot ash, increased roof strength and pitch against loading from ash
- Monitoring leading to prediction and early warning
- Public awareness, preparedness and response to warnings is vital
Probabilistic Seismic Hazard Assessment (PSHA)
Combines empirical data with models of physical processes, maps of source zones, the Gutenberg-Richter magnitude recurrence relationship, and ground motion prediction equations.
It accounts for sources of uncertainty in earthquake location and timing, magnitude, and ground motion parameters.
The outputs are seismic hazard curves and maps for different scenarios.
Mitigation of the seismic event itself is based on building codes that aim to change the dynamic behaviour of structures to reduce or avoid resonance
