formulation of a risk probability rating system for geohazard …119.92.161.2/portal/portals/21/eia...
TRANSCRIPT
Formulation of a Risk Probability Rating System for Geohazard and Environmental Risk Assessment
Katherine A. Hipol-Gavile Associate - Environment/ Geologist, AECOM, Taguig City Email: [email protected] The environmental impact assessment process has seen considerable
improvement over the years with respect to identification and characterization of
geohazard in parallel with local developments in the geosciences. However, one
aspect which is lacking is the determination of the frequency and likelihood of
occurrence for the identified geohazards for the purposes of impact and
environmental risk assessments. There is no officially established geohazard
frequency and probability rating in the Philippines comparable to international
rating systems such as those of the Federal Emergency Management Agency
(FEMA) and the United States Geological Survey (USGS). Due to this,
discussions of geohazard frequency and probability within the EIS are often
subjective and undervalued. Current developments in the country’s EIA system
and related regulatory requirements as well as integration of climate change
adaptation and disaster risk reduction schemes in the EIS call for the
establishment and adaptation of a similar rating system. The formulation and
adaptation of a geohazard risk probability rating system is vital in aiding
proponents, preparers and policy makers to 1) Formulate geohazard assessment
that is site specific; 2) Formulate applicable control measures considering the
likelihood of occurrence of the geohazard pre-mitigation; 3) Prioritize specific
geohazards in engineering design and controls; 4) Develop applicable hazard
scenarios to quantify asset loss in case of occurrence; 5) Promote interagency
(DENR-EMB, MGB, PHIVOLCS, and PAGASA) cooperation in formulating a
local hazard rating scheme; and 6) Communicate frequency and probability
assessment to stakeholders and policy makers to enable engagement and
participation in emergency response and disaster preparedness.
About the author
Katherine has about 10 years of experience in the
field of geology and environmental assessment that
include collaboration with foreign groups such as the
U.S Geological Survey. Currently, she works as the
lead for the geology, geohazard, and soils module in
environmental impact assessment and feasibility
studies for AECOM.
Formulation of a Risk Probability Rating System for Geohazard and Environmental Risk Assessment
Katherine A Hipol-Gavile Associate - Environment/ Geologist, AECOM, Taguig City Email: [email protected]
Introduction Due to the Philippines’ geographic location and tectonic setting, projects are generally
prone to different categories and varying degrees of geologic hazards. Moreover, it is
common that multiple geohazards are identified for a project site. Aside from sudden-
onset geohazards (i.e. earthquakes), evident climate change effects have brought about
emergence of geohazards that intensify over time (e.g. mass movement, erosion, and
flooding). While the Philippine Environmental Impact Statement (EIS) process requires
the comprehensive discussion of the geologic hazards and their corresponding impacts
and control measures, the discussions generally concentrate on the identification and
definition of the geohazards, with the assessment of the likelihood of occurrence and
the effects of climate change, undervalued. This paper presents methods and practices
that may improve geohazard impacts assessment in relation to the EIS and the
Environmental Risk Assessment (ERA) as well as the adaptation of a risk probability
rating scheme that may enable assessors and regulators to describe the potential
frequency and likelihood of the occurrence of geohazards for a particular site.
Geohazard Assessment in the Philippine EIA system Geohazards include all hazards that are entirely or partially caused by processes that
occur at the surface or the subsurface of the earth (Aurelio, 2004). Geohazards include
both instantaneous processes (i.e. earthquakes, volcanic eruptions) and chronic events
that develop over time and are often associated with climate change (Wood, 2008).
Recent years have seen the inclusion of hazards brought about by non-geologic
processes but are intensified by climate change (e.g. flooding). To summarize, the
geohazards discussions in the EIS consist of the following categories:
Geohazard Categories Specific hazards
1. Seismicity-related Ground shaking
Ground rupture
Liquefaction
Earthquake-related slope failure
Tsunami
2. Mass movement re
elated and rainfall-related)
Slope failu
(Earthquake-r
Subsidence
Differential Settlement
Creep
3. Volcanism-related earthquakes Volcanic
Lava flows
Pyroclastic flows
Lahar
Ash fall
Eruption-related tsunami
4. Others Erosion
Flooding
Storm surge
Seiches
Often, for a given project site, multip zards may occur that can sometimes
compound or enhance the baseline conditions’ natural susceptibility to particular
ologic events. Added challenges may also be encountered when a proposed project
le geologic ha
ge
changes the existing geomorphology and hydrologic conditions of an area creating
essentially a non-equilibrium or unstable condition. Most of the discussions for this
paper will focus on seismic hazard assessment as an example of an instantaneous
event, and mass movement that may include both instantaneous and non-
instantaneous events as impacted by climate change.
Seismic hazard Assessment The purpose of seismic hazard assessment is to determine the potential risks posed to
tive faults adjacent to or within the project site. Seismic
azard assessment also includes predictive determination of the response of the
identified sources; and
rical summation of contributions of all earthquake
rce.
tic and probabilistic
eismic hazard assessment for a project site. Earthquake frequencies for each source
Mass Movement Hazards Assessment
a project by the presence of ac
h
subsurface to an earthquake, the severity of which is largely dependent on subsurface
foundation properties and occurrence of zones of weaknesses. The seismic hazard
assessment approach consists of the following:
• Identifying seismic sources;
• Determining earthquake frequency from each source;
• Defining ground acceleration values from
• If possible, conducting nume
magnitudes at all distances from the site from each sou
The Philippine Institute of Volcanology and Seismology (PHIVOLCS) certification of
active faults remains a fundamental tool in conducting determinis
s
are determined from historical earthquake databases. In the absence of specific ground
acceleration equations in the Philippines, the equation developed by Fukushima and
Tanaka (1990) is used to define the ground acceleration values from identified sources.
Derived peak ground acceleration (PGA) values for a project site are then correlated
with the 475-year return period of probabilistic seismic hazard assessments from
Thenhaus and others (1996), U.S Geological Survey (2009) and the National Structural
Code of the Philippines (2001). These tools enable preparers to assess not only the
potential impacts of a seismic event to a project site, but also the likelihood of the
occurrence of an event within the project life.
The assessment of mass movement hazards, particularly slope failure, makes use of
e geohazard mapping outputs of the Mines and Geosciences Bureau (MGB) coupled
IS) tools and field surveys. Defining critical
lopes are usually conducted to determine areas susceptible to failure. However, the
he propensity for specific geohazards of a site can be determined through geologic
geology coupled with valuable tools such as GIS and geoscientific data.
he timing of geohazards however, cannot be accurately forecasted, and often,
probability rating was adopted. Risk probability rating descriptors were incorporated as
th
with Geographic Information System (G
s
importance of ground truthing to augment GIS tools and secondary information are
usually neglected. Field information is essential in identifying surface features that
indicate stress and potential failure, enabling the geohazard assessment and the
consequent recommendation of control measures to be more site specific. Identification
of previous occurrence of mass movement (e.g. landslide scarps, tension cracks, and
debris deposits) is valuable in determining not only the susceptibility of an area to failure
but also the type and likelihood by which these events may occur. The risk probability
descriptors for slope failure can thus be formulated from the proposed percentage range
or value vis-à-vis, for example, the impact area.
Risk Probability Rating System for Geohazards: A case study on past mining projects. T
mapping, identification of geomorphologic structures, and understanding of the
subsurface
T
approach to these events is reactionary. It should be noted that people also make
decisions based on forecasts and probabilities (e.g. probability of rain, fatality rates).
Though the occurrence of geohazards cannot be accurately predicted, risk probability
ratings for each geohazard category can be formulated to aid in drafting applicable
mitigating measures and prioritizing the implementation of specific engineering design
and controls based on the likelihood of occurrence.
The Tampakan Cu-Au Mine Project EIS is an example in which a preliminary risk
part of a geohazard assessment matrix to determine the likelihood of occurrence of a
pre-mitigation geohazard within the project site and the risks that it may pose during the
roject life.
, as well as the integration of climate change adaptation (CCA) and
isaster risk reduction (DRR) schemes in the EIS, will call for the establishment and
a probability risk rating system. The formulation and adaptation of a
eohazard rating system for the Philippines is vital in aiding proponents, preparers and
p
Conclusion Eventually, current developments in the country’s EIA system and related regulatory
requirements
d
adaptation of
g
policy makers to 1) Formulate geohazard assessment that is site specific; 2) Formulate
applicable control measures considering the likelihood of occurrence of the geohazard
prior to mitigation; 3) Prioritize specific geohazards in engineering design and controls;
4) Develop applicable hazard scenarios to quantify asset loss in case of occurrence; 5)
Promote interagency cooperation in formulating a local hazard rating scheme; and 6)
Communicate frequency and probability assessment to stakeholders and policy makers
to enable engagement and participation in emergency response and disaster
preparedness. It is important to emphasize that these efforts should be at an
interagency level between those whose main thrust are the geosciences anddisaster
preparedness, and business and government groups who will monitor, mitigate,
respond to or reduce the exposure of vulnerable systems such as the stakeholders and
their assets.
References
urelio, M.A. (2004). Engineering Geological and Geohazard Assessment (EGGA)
system for sustainable infrastructure development: the Philippine experience.
Engineering Geology for Sustainable Development in Mountainous Areas, Free
din (eds) Geological Society of Hong Kong, 7pp.
CH Australia (2009). Australian Master OHS and Environment Guide (2nd ed.).
http://w
A
and Ay
C
Federal Emergency Management Agency Earthquake Hazard Maps
ww.fema.gov/earthquake/earthquake-hazard-maps
.H. and Milner, K.R. (2007). Forecasting California’s Earthquakes –What can we
expect in the next 30 years. U.S Geological Survey Fact
Field, E
Sheet, Stauffer, P.H and
tion for Horizontal
in Japan. Bulletin of the
Hillson
EA Proceedings, 7 pp.
ard in the Philippines. National
Wood, ce to Natural Hazards. U.S
Hendley J.W (eds) 2 pp.
Fukushima, Y., and Tanaka, T. (1990), A New Attenuation Equa
Acceleration of Strong Earthquake Ground Motion
Seismological Society of America, 80, 757-783.
, D.A. (2005). Describing probability: The limitations of natural language. PMI
Global Congress 2005 EM
Thenhaus, P.C., Hanson, S.L., Algermissen, S.T., Bautista, B., C., Bautista, M.L.P.,
Punongbayan, B., Rasdas, A. R., Nillos, J. and Punongbayan, R.S. (1994).
Estimates of the Regional Ground Motion Haz
Disaster Mitigation in the Philippines, DOST-PHIVOLCS, 1994.
N. (2011). Understanding Risk and Resilien
Geological Survey Fact Sheet, Stauffer, P.H and Hendley J.W (eds) 2 pp.
Formulation of a Risk Rating System for Geohazard and Environmental Risk Assessment
Katherine H. GavileAssociate, Environment
June 20, 2013
Hazards are defined as:
Events or physical conditions that have the potential to cause fatalities, injuries, property damage, infrastructure damage, agricultural loss, damage to the environment, interruption of business, or other types of harm or loss (FEMA, 1997)
FEMA. 1997. Multi Hazard Identification and Assessment. FEMA. Washington, D.C.
While Geologic Hazards or Geohazards:
“Include all hazards that are entirely or partially caused by processes that occur at the surface or the subsurface of the earth (Aurelio, 2004).
The Philippines’ tectonic and geographic setting makes most of the country susceptible to different geohazards.
As the population grows, more projects, developments, settlements and people are situated in areas that are prone to geohazards.
The Environmental Impact Assessment (EIA) process requires the comprehensive discussion of the geologic hazards and the corresponding impacts and control measures along with the integration of Climate Change Adaptation and Disaster Risk Reduction.
Geologic Hazard Assessment within the Philippine EIA System
Environmental Impact Statement
Key Baseline Information
The LandThe WaterThe AirThe People
Environmental Risk Assessment
Environmentally Critical Areas
Geology, Geomorphology, and Geohazards
The focus of discussion is mostly on identification of the geologic hazards and thorough assessment is often undervalued.
Geologic Hazard Categories
Geohazard Categories Specific hazards
1. Seismicity-related
Ground shaking
Ground rupture
Liquefaction
Tsunami
2. Mass movement
Slope failure
Subsidence
Differential Settlement
Creep
Geologic Hazard Categories
Geohazard Categories Specific hazards
3. Volcanism-related
Volcanic earthquakes
Lava flows
Pyroclastic flows
Lahar
Ash fall
Eruption-related tsunami
4. Others
Erosion
Flooding
Storm surge
Seismic Hazards
Inquirer.net
August 2, 1968 – Mw 7.3 at Casiguran, Aurora
August 16, 1976 – Mw 8.0 at Moro Gulf
July 16, 1990 – Mw 7.8; 25 km-long ground rupture that stretched from Aurora to Nueva Ecija
August 31, 2012 – Mw 7.6 at Samar
Seismic Hazard Assessment
The purpose of seismic hazard assessment is to determine the potential risks posed to a project by the presence of active faults adjacent to or within the project site.
Seismic hazard assessment also includes predictive determination of the response of the subsurface to an earthquake, the severity of which is largely dependent on subsurface foundation properties and occurrence of weaknesses.
Seismic Hazard Assessment
The seismic hazard assessment approach consists of the following:
Identifying seismic sources;
Determining earthquake frequency from each source;
Defining ground acceleration values from identified sources; and
If possible, conducting numerical summation of contributions of all earthquake magnitudes at all distances from the site from each source.
Seismic Hazard Assessment
The PHIVOLCS certification of active faults remains a fundamental tool in conducting deterministic and probabilistic seismic hazard assessment for a project site.
The PHIVOLCS certification of active faults is fundamental in identifying potential earthquake generators and determining the instance of seismic sources to a project site.
Seismic Hazard Assessment
In the absence of specific ground acceleration equations in the Philippines, the equation developed by Fukushima and Tanaka (1990) is used to define the ground acceleration values from identified sources.
* Based on Fukushima and Tanaka - Bulletin of Seismological Society of America, August 1990
Seismic Hazard Assessment
Parameters
Eastern Section Central Section Western Section
9.91 km west of
unnamed Fault
19 km south-west of Fault A
9.85 km south of unnamed
Fault
38.02 km north-east
of Mindanao Fault-
11.65 km south-east
of unnamed Fault
25.71 km south-west of Fault A
Radius (km) 9.900 19.000 9.800 38.000 11.600 25.700
Magnitude (M) 7.500 7.500 7.500 7.500 7.500 7.500
Acceleration (cm/sec2) 457.709 358.328 458.498 231.537 435.703 304.200
Rock (60% of g)* 0.280 0.219 0.280 0.142 0.266 0.186
Hard Soil (107% of g)* 0.499 0.391 0.500 0.253 0.475 0.332
Medium Soil (87% of g)* 0.406 0.318 0.407 0.205 0.386 0.270
Soft Soil (139% of g)* 0.649 0.508 0.650 0.328 0.617 0.431
Table 3.1-16 Calculated G-values for Defined Faults and Seismic Responses per Subsurface Material* Based on Fukushima and Tanaka - Bulletin of Seismological Society of America, August 1990
Seismic Hazard Assessment
Derived PGAs for a project site are then correlated with the 475-year return period of probabilistic seismic hazard assessments from Thenhaus et.al. (1996), U.S Geological Survey (2009) and the National Structural Code of the Philippines (2001).
Seismic Hazard Assessment
Coupled with probabilistic seismic hazard analysis, it is also important to note the historical earthquake occurrence or distribution for a given site to assess the active earthquake generators and the probability that an earthquake of a certain magnitude will occur.
United States Geological Survey (USGS) NorthernCalifornia Earthquake Data Center (NCEDC) AdvancedNational Seismic System (ANSS) online global earthquakecatalog database.
Seismic Hazard Assessment
From Yuen et.al. (2000)
Seismic Hazard Assessment
While the identification of seismic hazards associated with potential activities of the nearest active faults or earthquake generators is vital. Assessment should go beyond mere identification for it to be more site and project specific.
The Working Group on California Earthquake Probabilities (WGCEP) recommends estimating seismic hazard probabilities or composite forecasts based on seismology, geology, geodesy, and paleoseismology(Field and Milner, 2007).
Mass Movement
August 2, 1999
November 2004 Blogs.agu.org
Earthdata.nasa.gov
February 17, 2006
Assessment for Mass Movement Hazards
• Geology
• Slope shape and geomorphology
• Concentration of surface water
• Presence and depth to groundwater
• Material strength
Assessment for Mass Movement Hazards
USDA recommends the delineation of 18% slopes as critical.
However, for the Philippines, slope failure susceptibility is determined not only by slope gradient but an interplay of factors such as climate, geology, vegetation, soil type, and surface hydrology.
Tools that can be used include GIS, secondary data, and most importantly, ground truthing.
Assessment for Mass Movement Hazards
Impact Assessment Criteria and Rating Scales
Criteria Rating ScalesStatus • Positive
• Negative• Neutral
Extent (spatial limit of the impact)
• Local (site-specific or immediate surrounding area)• Regional (Province)• National (Country)
Duration(predicted lifetime of the impact)
• Short-term (0 – 5years)• Medium Term (6 – 15 years)• Long Term (16 years and beyond and where it is assumed the impact will cease after the operational life of the project)
Impact Assessment Criteria and Rating Scales (cont.)
Criteria Rating ScalesIntensity (severity of the impact) • Low (minimal)
• Medium (environment is alteredbut processes continue in a modified manner)• High (permanent or long-term substantial change)
Probability (Likelihood of occurrence)
• Improbable or Rare• Probable – equivalent to Unlikely, < 50% chance or possibility to occur within or after the project life• Highly Probable - equivalent to Possible, 50 to 90% chance or will occur within project life• Definite – equivalent to Likely, >90% chance of occurring or will occur regardless of mitigation measure
Probability Risk Rating System
The timing of geohazards, cannot be accurately forecasted and often, approach to these events is reactionary.
Note that people also make decisions based on forecasts and probabilities (e.g. probability of rain, fatality rates).
Though the occurrence of geohazards cannot be accurately predicted, risk probability ratings for each geohazard category can be formulated to aid in drafting applicable mitigating measures and prioritizing the implementation of specific engineering design and controls based on the likelihood of occurrence.
Probability
• Classical: Probability of getting 2 heads in 3 flips of a coin
• Subjective: Probability of the Philippines becoming no.16 in economy by 2050
• Frequency: Probability of an Ondoy-like rainfall over a 120 year period
Jardine and Hrudley, 1997. “Mixed Messages in Risk Communication”
PROBABILITY DESCRIPTION
ALMOST CERTAIN 1 in 10 chance LIKELY TO OCCUR
LIKELY 1 in 100 chance WILL PROBABLY OCCUR
POSSIBLE 1 in 1000 chance MAY OCCUR OCCASIONALLY
UNLIKELY 1 in 10,000 chance DO NOT EXPECT TO HAPPEN
RARE 1 in 100,000 chance DO NOT BELIEVE WILL EVER HAPPEN
Australia / New Zealand Model (AS/NZS 4360: 1999)
Criteria Rating ScalesProbability(Likelihood of occurrence)
• Improbable – equivalent to FEMA rating of Rare
• Probable – equivalent to Unlikely, < 50% chance or possibility to occur within or after the project life
• Highly Probable - equivalent to Possible, 50 to 90% chance or will occur within project life
• Definite – equivalent to Likely, >90% chance of occurring or will occur regardless of mitigation measure
Thank You