National Environment & Planning Agency (NEPA), Kingston & St.
Andrew Parish Disaster Committee (KSAPDC), and Kingston & St.
Andrew Corporation (KSAC)
SYMPOSIUM:
SUSTAINABLE HOUSING- KINGSTON and ST. ANDREW
14 October 2004
Courtleigh Hotel, Kingston, Jamaica
HAZARD MAPPING AND SITE SUITABILITY
WITH SPECIAL REFERENCE TO
KINGSTON & ST. ANDREW, JAMAICA
BY
RAFI AHMAD
Unit for Disaster Studies, Department of Geography
& Geology, the University of the West Indies at
Mona, Kingston 7, Jamaica.
[email protected]
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
REFERENCES FOR DETAILED INFORMATION:
•
(1) Unit for Disaster Studies website for information on natural
hazards and hazard maps: http://www.mona.uwi.edu/uds/
•
(2) See power point presentation on Natural hazard maps in
Jamaica: http://www.mona.uwi.edu/uds/Jamaica%20Hazard%20maps_files/frame.htm
•
Complete article: Ahmad, Rafi, 2004, Natural hazard maps in
Jamaica: foundations for sustainable development,
Proceedings National Conference on the Environment,
Organized by Jamaica Institute of Environmental Professionals,
April 2003, Jamaica Institute of Environmental Professionals,
Kingston, Jamaica, < www.jiep.org>, pp.6.1 to 6.25.
•
(3) “Kingston, Jamaica: environment and hazards” is included
in a CDROM. This is an extract from the article “Urban
steeplands in the tropics: an environment of accelerated
erosion” by A. Gupta and Rafi Ahmad, published in GeoJournal,
vol.49, p.143-150, 2000 (for1999).
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
The Presentation:
This paper reviews
• natural hazards in Kingston and St. Andrew
• status of natural hazard maps available for Kingston
and St. Andrew that facilitate vulnerability and risk
assessment
• potential uses of hazard maps in guiding housing and
infrastructural development
• A list of GIS based hazard maps prepared in the
1990’s under Caribbean Disaster Mitigation Project
(CDMP)
• we use UWI landslide hazard mapping in the Kingston
Metropolitan Area as an example to show the utility of
some of the hazard maps in the context of rainfall
induced slope movements associated with September
Reproduced
with permission of
10-12, 2004 hurricane
Ivan.
UDS. http://mona.uwi.edu/cardin
Plate tectonic setting of Jamaica
From: National Geographic Magazine
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Natural hazards in the Caribbean
From: Munich Re, 2002.
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Understanding Landslides (slope movements) for
hazard evaluation and site specific investigations:
• Gravity is the driving force producing slope
instability.
• Strength of materials making up the slope resists the
action of gravity. This prevents landslides from
occurring.
• The balance between gravity acting on the slope and
resistance by the slope material usually favours
resisting slope materials. When this balance shifts to
being equal or slightly favouring gravity, a landside
is imminent.
• While gravity acts at a constant rate, changes
happen which increases the shear stress of gravity
as it acts on the slope, reduce the resisting strength
of the slope material, or a combination of both.
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Landslides continued:
• This alters the balance between driving and resisting
forces. If the change is sufficiently great, it may trigger
a landslide.
• Engineers describe slope stability using the term
FACTOR OF SAFETY- ratio of resisting to driving
forces. FS>1=Stable slope.
COMMON FACTORS PRODUCING INSTABILITY:
• Removing lateral support to part of the slope
• Surcharging the slope
• Increasing water in slope-pore-water pressures
• Dynamic stress
• Changing slope morphology and hydrology, strength of
slope materials.
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
•
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•
•
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Hazard, vulnerability, and risk with respect to
landslides: international terms
Hazard: as represented by susceptibility, which is
the likelihood of a potentially damaging landslide
occurring within a given area.
Vulnerability: the level of population, property,
economic activity, including public services etc. at
risk in a given area resulting from the occurrence of
a landslide of a given type.
Risk (specific): the expected degree of loss due to a
particular landslide phenomenon.
Zonation: division of land surface into areas and
ranking of these areas according to degrees of
actual or potential hazard from landslides- generally
shown on 2 or 3- dimensional maps.
Hazard maps change
as ground surface changes.
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Types of landslide hazard maps:
• Landslide Inventory Map: shows the location and
outlines of landslides. Inventory is a data set that
may represent a single or multiple events.
• KMA inventory has >2,500 landslides of different
types.
• Landslide Susceptibility Map: ranks relative slope
stability in an area into categories that range from
stable to unstable. It shows where landslides may
form.
Several Maps in Jamaica.
• Landslide Hazard Map: indicates the annual
probability (likelihood) of landslides occurring
throughout an area.
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Hazard Maps contd.
• Landslide Risk Map: shows the
expected annual cost of landslide
damage throughout an area.
• Risk maps combine the probability
information from a hazard map with an
analysis of all possible consequences.
(Based on KMA Landslide Hazard
Project and U.S. Geological Survey).
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Examples of Inventory Maps for Kingston and St.
Andrew:
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Inventory Map from Irish Town and Gordon
Town areas
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Irish Town Road Landslide, 1988 ( Tyndale Biscoe Photo)
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Landslides in Jacks Hill area:
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Landslides affecting roads, power lines, and domestic
water supplies.
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Vertical Aerial Photograph of
Liguanea Ridge:
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Landslide Inventory Map of the Liguanea Ridge and
geological sturcture.
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Simplified geology and structure of the
Liguanea Plain.
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Landslide and flooding processes in KMA:
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Landslide Isopleth Map for KMA:
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Landslide Susceptibility Map for KMA
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Guidelines for use of KMA Landslide Suceptibility Map
• Low Susceptibility (colour code blue): Areas
for which the combination of factors is
generally unlikely to adversely influence
slope stability. Site development to be
guided by normal planning and other
building regulations.
• Moderate Susceptibility (colour code green):
Areas for which the combination of factors is
less likely to adversely affect the stability
provided that the existing ground conditions
are not radically altered to facilitate site
development.. The scale and nature of
proposed development should be taken into
consideration.
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Guidelines contd.
• Moderate-high Susceptibility (colour code
yellow): Areas for which the combination of
factors may adversely influence slope
stability. Slopes are covered with a thick
blanket of weathered rock and colluvium
(debris) which when disturbed are prone to
landslides. Debris flows should be
anticipated. Development may proceed
based on geologic-geotechnical
investigations and advice . The cost of
investigations and remedial and/or
preventive measures are likely to be high.
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Guidelines contd.
• High Susceptibility (colour codes purple and
red): Areas for which existing ground
conditions are likely to create serious
landslide problems. It includes areas near
faults and fault scarps. In general, these
areas are unsuitable for site development.
• The cost of carrying out standard geologicgeotechnical investigations and
remedial/preventive work for slope
stabilization may be very high. Therefore, it
is best to avoid these slopes as far as
possible except for the most essential use. A
thorough ground investigation report by
competent persons should be required
before any site development is undertaken.
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin
Conclusions:
• We consider hazard mapping and hazard
maps as a first step in the complex
communication chain that links land use
planning, sustainable development, and lossreduction from natural disasters.
• Societal acceptance and effective use of
hazard maps prepared for Jamaica in the
1990’s lies somewhere ahead in the future.
• In the mean time there must be a mechanism
to capture user generated feedback on
existing hazard maps.
Reproduced with permission of
UDS. http://mona.uwi.edu/cardin