7. The role of Civil Engineers in ex-ante risk reduction

Question 1

What is ‘ReliefWeb’?

Answer 1

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).

Question 2

UNISDR definitions for ex-ante DRR actions: prevention

Answer 2

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.

Question 3

UNISDR definitions: mitigation

Answer 3

The lessening or minimizing of the adverse impacts of a hazardous event.

Question 4

UNISDR definitions: preparedness

Answer 4

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.

Question 5

Summary of possible ex-ante DRR actions.

Give the descriptions for each of the following type of action:
Hazard reduction
Mitigation
Preparedness

Answer 5

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

Question 6

Define risk identification

Answer 6

recognise and describe the risks (may be associated with a single hazard or multi-hazards) and the scope of the assessment

Question 7

Define risk analysis

Answer 7

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)

Question 8

Define risk evaluation

Answer 8

compare risk with risk criteria (acceptable, tolerable, unacceptable)

Question 9

Landslide hazard reduction, 3 slope stabilisation measures

Answer 9

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

Question 10

4 types of models for assessing landslides

Answer 10

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

Question 11

Landslide mitigation: reducing exposure diagram

Answer 11

DRAW IT OUT

Question 12

Types of flood

Answer 12

River floods (fluvial) 
Surface water floods (pluvial)
Groundwater floods
Sewer floods
Coastal floods

Question 13

Flood and hazard assessment in the UK

Answer 13

Models
Maps
Forecasting

Question 14

Flood risk management UK case studies

Answer 14

SUDS and working with natural processes
Temporary defences, flood controls (hydro-break
Managed coastal realignment
Property-level flood resilience

Question 15

Structural measures for flood hazard reduction and mitigation

Answer 15

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

Question 16

Reducing vulnerability to floods - what measure is used in the Netherlands

Answer 16

Flood resilient buildings. Floating amphibious homes on flexible mooring posts

Question 17

Volcanic hazards overview
Primary hazards (3)
Secondary hazards (6)

Answer 17

Primary hazards: lava and pyroclastic flows, tephra falls, gases

Secondary hazards: lahars, landslides, floods, tsunamis, tremors, atmospheric effects (ash clouds and air pollution)

Question 18

Volcanic eruptions overview, types of eruption

Answer 18

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)

Question 19

3 parts of volcanic assessment, (9)

Answer 19

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

Question 20

Volcanic hazard mitigation, early warning and preparedness, 4 measures

Answer 20

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

Question 21

Earthquakes are generally associated with _____ ____ ____ whose movements relative to eachother can be described as: (3)

Answer 21

tectonic plate boundaries

divergent, convergent (subduction) and transform

Question 22

Different types of EQ faulting mechanism (4)

Answer 22

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

Question 23

What are seismic waves, and what are the two types?

Answer 23

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)

Question 24

How are observations of P and S waves made?

How are seismic hazards indicated?

Answer 24

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.

Question 25

EQ damage prediction and mitigation

Answer 25

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

Question 26

What 3 main things do seismic building codes consider?

Answer 26

Importance of building materials and structural design (reinforced masonry structures bad)

Other (building shapes, geology, connections)

Strategies (upgrade existing structures, dampening, base isolation

Question 27

Principles for EQ resistant design

Answer 27

Stable foundations, continuous load paths, adequate stiffness and strength, regularity, redundancy, ductility, rugedness