Geoscience Reference
In-Depth Information
• The defi nition of the level of susceptibility of the sector, qualitative
expression of destructive process occurrence probability.
The criteria currently used in the preparation of the diagnostic report
for identifi cation and classifi cation of risk situations is based on work by
Cerri & Carvalho 'Hierarchy of Risk Situations in slums in São Paulo'
(Carvalho 1990), updated based on the criteria most recently practiced and
is described below:
• No risk: Stable sectors, the geotechnical point of view, providing
adequate security against the cases examined, whose topography has
a slope less than 15% whatever the conditions of occupation or even
30% since the houses have adequate containment of the slope;
• Risk 1-Low: Situations which have not been identifi ed and where
instability processes maintaining the status quo, do not expect the
occurrence of destructive events, but where the steepness of the slopes
is between 15 to 30% and the houses are poor and/or do not promote
proper containment of the slope, or where the steepness of the slope
exceeds 30%, whatever the type of occupation;
• Risk 2-Medium: Situations where the processes of destabilization meet
with development potential, but there is no evidence of instability.
Low probability of occurrence of destructive events during episodes
of intense and prolonged rainfall, implying the possibility of a smaller
number of fatal victims, in case of instability, or where the steepness
of the slopes is between 30 and 45% and existing buildings are poor
houses and/or do not promote proper containment of the slope,
or slopes where the inclination exceeds 45%, whatever the type of
occupation;
• Risk 3-High: Situations where the processes of instability are early stage
or with high development potential and the evolution of processes
is likely within the established period of observation (one year). The
probability of the occurrence of destructive events during episodes of
intense and prolonged rainfall, implys the possibility of a large number
of casualties, in case of instability. Places where the steepness of the
slopes is between 45 and 60% and existing buildings are poor houses
and/or do not promote proper containment of the slope, or slope where
the inclination exceeds 60%, whatever the type of occupation;
• Risk 4-Very High: Situations where the destructive processes are in an
advanced stage of development. The indicators of instability (cracks
in the soil, abatement steps on slopes, cracks in houses or retaining
walls, tilted poles or trees, slip scars, etc.) are present, revealing a
high probability of destructive events during episodes of heavy and
prolonged rains, requiring urgent intervention to prevent loss of life.
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