7. The role of Civil Engineers in ex-ante risk reduction Flashcards
What is ‘ReliefWeb’?
ReliefWeb is the leading humanitarian information source on global crises and disasters. It is a specialized digital service of the UN Office for the Coordination of Humanitarian Affairs
(OCHA).
UNISDR definitions for ex-ante DRR actions: prevention
Activities and measures to avoid existing and new disaster risks.
The term is not widely used nowadays, probably because its not really possible to prevent hazards.
UNISDR definitions: mitigation
The lessening or minimizing of the adverse impacts of a hazardous event.
UNISDR definitions: preparedness
The knowledge and capacities developed by governments, response and recovery organizations, communities and individuals to effectively anticipate, respond to and recover from the impacts of likely, imminent or current disasters.
Summary of possible ex-ante DRR actions.
Give the descriptions for each of the following type of action:
Hazard reduction
Mitigation
Preparedness
Hazard reduction - reduce likelihood of a hazard occurring
Mitigation - control the size or path of the hazard
- reduce overall exposure to the hazard
- reduce vulnerability of exposed elements to damage
Preparedness - early warning to reduce short-term exposure to hazard
- build capacity to improve response and recovery
Define risk identification
recognise and describe the risks (may be associated with a single hazard or multi-hazards) and the scope of the assessment
Define 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)
Define risk evaluation
compare risk with risk criteria (acceptable, tolerable, unacceptable)
Landslide hazard reduction, 3 slope stabilisation measures
Reducing driving forces: reduce slope gradient, improve drainage
Increasing the resisting forces: reinforce with soil nails, rock anchors, geotextiles etc. or retain with gravity retaining walls, gabions etc.
Replacing materials: excavate and reform with a denser surface soil layer
4 types of models for assessing landslides
Analytical - Static Equilibrium Analysis, wedge analysis, method 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
Discrete element models - Movement of individual rigid elements, from grain scale to blocks of material
Landslide mitigation: reducing exposure diagram
DRAW IT OUT
Types of flood
River floods (fluvial) Surface water floods (pluvial) Groundwater floods Sewer floods Coastal floods
Flood and hazard assessment in the UK
Models
Maps
Forecasting
Flood risk management UK case studies
SUDS and working with natural processes
Temporary defences, flood controls (hydro-break
Managed coastal realignment
Property-level flood resilience
Structural measures for flood hazard reduction and mitigation
Flood defences and protection; barriers, embankments (temp/perm)
Conveyance; routing potential flood waters via natural or artificial channels f(channel cross section, slope, frictional resistance): straightening channels, increasing bank heights, dredging, relief channels, culverts
Storage; attenuation of surface water runoff reduces peak flows within the channel: on-line and offline 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
GW management; part of the catchment water storage system and also used as a water supply; recharge vs extraction, protect from pollution, alternative water supplies
Wetlands and environmental buffers
Building design, resilience and resistance
Reducing vulnerability to floods - what measure is used in the Netherlands
Flood resilient buildings. Floating amphibious homes on flexible mooring posts
Volcanic hazards overview Primary hazards (3) Secondary hazards (6)
Primary hazards: lava and pyroclastic flows, tephra falls, gases
Secondary hazards: lahars, landslides, floods, tsunamis, tremors, atmospheric effects (ash clouds and air pollution)
Volcanic eruptions overview, types of eruption
Depend on magma sources, locations (subduction zones, hotspots or rifts) and resulting minerals. Felsic or acid (high gas content, viscous and explosive) versus mafic or basic (low gas content, low viscosity, less violent)
o Plinean (columns of gas and ash ejected; pumice falls and gas blasts) o Pelean (pyroclastic flows, lateral blasts and viscous lava flows giving steep sided cones) o Vulcanian (ash-laden gas explosions) o Strombolian (incandescent cinder, lapilli and lava bombs) o Icelandic (low viscosity basaltic lava, parallel fissures, rift) o Hawaiian (low viscosity, fire fountains, fast flowing over long distances)
3 parts of volcanic assessment, (9)
1) Historical evidence and experience
2) Geological mapping
3) Monitoring, prediction and warning
Volcanic monitoring types and methods employed by the USGS Volcano Hazards Program: thermal imaging, satellite, GPS, surveying, ground vibration, cameras
Volcanic hazard mitigation, early warning and preparedness, 4 measures
Controlling lava flows: - Explosives, artificial barriers, water sprays…. limited effectiveness
Controlling lahars and debris flows: - sediment traps, diversion barriers
Resilient buildings (giving temporary shelter if warning times are limited): - o Strengthening structures to withstand tremors and debris impacts o Doors and window shutters to resist hot ash o 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
Earthquakes are generally associated with _____ ____ ____ whose movements relative to eachother can be described as: (3)
tectonic plate boundaries
divergent, convergent (subduction) and transform
Different types of EQ faulting mechanism (4)
normal, reverse, strike slip, oblique
Strains can accumulate in such zones until the plates shift and seismic waves are generated along the fault plane. There are different types of faulting mechanism described in terms of the relative movement of blocks
What are seismic waves, and what are the two types?
Seismic waves are classified as body waves (P wave: fast and small amplitude; and S wave: slow and large amplitude) and surface waves (Love waves and Raleigh waves)
How are observations of P and S waves made?
How are seismic hazards indicated?
Using accelerometers and seismometers which can measure the acceleration, velocity and displacement-time history, allowing estimation of epicentre location
Seismic hazard is indicated by ground motion intensity (peak ground acceleration and peak ground velocity – PGA and PGV) which is proportional to earthquake magnitude and decreases with distance from the epicentre. They are also affected by local ground conditions.
The ground motion (‘shaking’) at a specific site will determine the damage to structures.
EQ damage prediction and mitigation
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
What 3 main things do seismic building codes consider?
Importance of building materials and structural design (reinforced masonry structures bad)
Other (building shapes, geology, connections)
Strategies (upgrade existing structures, dampening, base isolation
Principles for EQ resistant design
Stable foundations, continuous load paths, adequate stiffness and strength, regularity, redundancy, ductility, rugedness
