Apresentação oral sobre a metodologia do mapeamento

1. Methodological procedures to landslide
risk mapping in Brazilian slums
Presenter
Luciana Pascarelli Santos
Authors
Eduardo Soares de Macedo(1), Kátia Canil(1), Fabrício Araujo Mirandola(1), Fabiana Checchinato Silva(1), Marcelo
Fischer Gramani(1), Agostinho Tadashi Ogura(1), Alessandra Cristina Corsi(1), Luciana Pascarelli Santos(2)
(1) Institute for Technological Research – IPT , São Paulo (SP), Brazil
(2) São Paulo City Council, São Paulo (SP), Brazil

2. Description of mapping methodology
In this methodology, the factors that make assessment and risk analysis are
simplified, grouped and analyzed qualitatively, from direct observation in the
field. In this sense we have evaluated the following factors, considered essential
to risk analysis:
• typology of the expected process and its probability or possibility of occurrence;
• vulnerability of urban settlements; and
• potential damage.

3. Stages of the mapping methodology
In accordance with the requirements, the specific objectives of the performed activities
were the following:
• to obtain low-altitude oblique photos of the areas at risk from helicopter overflights;
• identify the sectors with different degrees of probability of occurrence of destructive
processes (landslides on slopes and/or washouts of stream banks) and enclose them in the
oblique photos;
• indicate the number of threatened houses or buildings that could be affected due to the
occurrence of the destructive processes mentioned above;
• present alternative measures to control the identified risks;
• design a database containing the results of the mapping.

4. Description of mapping methodology
In the areas selected by the council were performed:
• a survey of the area occupation characteristics and its infrastructure
CATEGORY OF
CHARACTERISTICS
OCCUPATION
Densely occupied areas, with basic
Consolidated area
infrastructure.
Areas in process of settlement,
adjacent to areas of established
Partially consolidated
occupation. Density of occupation
area
ranging from 30% a 90%. Reasonable
basic infrastructure.
Expansion areas, remote and distant
from urban nucleus. Low density of
Split area
occupation (up to 30%). Devoid of basic
infrastructure.
In such cases, characterize the area
Mixed area with regard to occupation density and
implementation of basic infrastructure

5. Description of mapping methodology
• risk mapping procedures using geological and geotechnical surface investigations in order
to identify the types of gravitational mass movements
CHARACTERISTICS OF THE
PROCESSES
MOVEMENT/MATERIAL/GEOMETRY
- several (internal) displacement planes / -
very low to low (cm/year) velocities that
decrease with depth / - constant, seasonal
CREEP
or intermittent movements /- soil, deposits,
altered/fractured rock /- undefined
geometry
- few (external) displacement planes / -
medium (m/h) to high (m/s) velocities / -
small to large volumes of material
- variable geometry and material / PLANAR:
SLIDES
thin soils, soils and rocks with one weakness
plane / CIRCULAR: homogeneous thick soils
and very fractures rocks / WEDGE: soils and
rocks with two weakness planes
- no displacement planes / - free fall- or
inclined plane-type movement / - very high
(several m/s) velocities
FALLS - rocky material / - small to medium
volumes / - variable geometry: flakes,
plates, blocks, etc. / BOULDER ROLLING /
TOPPLING
- many displacement surfaces (internal and
external to the moving mass) / - movement
similar to that of a viscous liquid / -
development along drainage / - medium to
FLOWS
high velocities / - soil, rock, debris and
water mobilization / - large volumes of
material / - extensive range, even in flat
areas

6. Description of mapping methodology
• as well as the constraints of the destabilizing processes, evidence of instability and
indication of the development of destructive processes. Thus the prevailing destabilizing
processes will be identified, delimiting and characterizing the risk sectors.
MOVEMENT
SITE CHARACTERIZATION
EVIDENCE
- Natural slope - Presence of blocks - House
- Cut slope of rock/boulders/rock cracks/landfill
- Slope height walls - Trees/poles/walls
- Compacted fill - Presence of inclination
- hauled fill trash/debris - Etch-plains
- Distance from - Amphitheater - Landslide scars
home Landfill - Swollen walls
- Declivity - Occupation of - Erosion features
- Unfavorable headwaters - Stream margins
structures in undermining
soil/rock
PRESENCE OF
PRESENCE OF WATER
VEGETATION
- Surface concentration of stormwater - Trees
- Release of wastewater into surface - Undergrowth
- Presence of septic tanks/sewage/water - Deforested area
mains - Farming area
- Upwelling water
- Leakings

7. Field activities
The materials to be used to obtain the support information and product to the risk
mapping are:
• vertical aerial photos, with appropriate scale, up to 1:5.000;
• copies of the plano-altimetric maps, basis for the indicated mapping areas;
• information on risk areas, such as development records and/or occurrences of instability
processes, copies of technical reports and expert opinions previously prepared, any
intervention guidelines proposed (implemented or not) etc.;
• technical publications, geological, geotechnical, geomorphological and slope angle maps,
with information on areas indicated for risk mapping;
• copy of the street guide page on which is located the chosen mapping area.

8. Log LOCALIZAÇÃO DA ÁREA
FICHA PARA AVALIAÇÃO DE ÁREA DE RISCO
A log is a tool to determine the potential of Endereço: Área nº:
accidents through field surveys carried out in order SITUAÇÃO DA ÁREA (VIDE MODELOS ANEXOS)
to identify risk situations. The cards used in field ( ) Encosta ( ) Margem de córrego ( ) Encosta + Margem de córrego
CIRCUNST ÂNCIAS EM QUE SE DESENVOLVEM OS PROCESSOS
surveys should contain the aspects to be analyzed
MARGEM DE CÓRREGO ENCOSTA
(check list), allowing the professional come to a
conclusion as to the risk of the analyzed area.
Distância observada:______ m Distância observada:______ m
( ) Concentração ou lançamento de águas em superfície ( ) Pontos de infiltração ou minas
( ) Presença de vegetação. Qual? ________ ( ) Área desmatada ( ) Presença de lixo e entulho
( ) Trechos aterrados ou escavados ( ) Outros. Citar:_______________
EVIDÊNCIAS DE PROCESSO DE INSTABILIZAÇÃO
( ) trincas/rachaduras ( ) degraus de abatimento ( ) muros embarrigados
( ) cicatrizes de escorregamento ( ) árvores/postes inclinados ( ) outros. descrever:___________
Nº DE MORADIAS (A SEREM) HÁ POSSIBILIDADES DE CONVIVÊNCIA
EFETIVAMENTE ATINGIDAS COM O RISCO? POR QUÊ?
GRAU DE PROBABILIDADE DE OCORRÊNCIA DE PROCESSO DE INSTABILIZAÇÃO
( ) R1 – Baixo ( ) R2 – Médio ( ) R3 – Alto ( ) R4 – Muito Alto
RESPONSÁVEL PELAS INFORMAÇÕES:

9. Overflight
Overflights by helicopter should be preceded by flights planning supported by technical field visits in
order to obtain coordinates from the GPS readings.
Besides the programming of helicopter overflights, all the technical material will allow the
optimization of the field activities, as well as a preliminary analysis of the areas to be mapped,
allowing for a fast and efficient mapping.

10. Description of mapping methodology
The risk sectors will be delimited with the indication of the probable destabilizing processes, that is,
landslides on natural slopes or cutting slopes and embankments. The criteria for judging the
probability of the destabilizing processes of occupied slopes landslides kind, as well as the
parameters analyzed for further procedures.
PROBABILITY DEGREE
R1 - Low Risk R3 - High Risk
Concerning to evaluated Concerning to evaluated
indicators, the area shows indicators, the area shows high
low risk to develop landslides risk to develop landslides
processes processes. Relevant indicators
of instability processes can be
observed
R2 - Medium Risk R4 - Very High Risk
Concerning to evaluated Concerning to evaluated
indicators, the area shows indicators, the area shows very
medium risk to develop high risk to develop landslides
landslides processes. Just processes. Almost all the
some indicators of instability indicators of instability
processes can be observed. processes can be observed. It is
the most critical condition.

11. Representation of sectors in the oblique photos
For the representation of the sectors at low-altitude oblique photos the following procedures,
criteria, symbols and conventions were adopted
• on the oblique photos, with the delimited risk factors the identification of the houses to be removed is
done with the letter “r”;
• in cases where the same sector is represented in more than one oblique photo, preference should be
given to the photo where the sectors can be better seen and their boundaries more precise.

12. Final Comments
For The risk mapping allows an assessment of the areas aiming to provide immediate, medium and
long term solutions for the slums in the most critical situation.
The obtained results will enable the city administration develop a strategic plan of interventions to
reduce and control the mapped risks, enabling the cost estimate for the suggested interventions for
each sector and the establishment of sequence of priorities for the implementation in accordance
with the technical criteria.
An example of applying this methodology can be seen in the paper entitled “Mapping of geological
at-risk areas in the city of São Paulo: issues and results from the largest survey of risk in Brazil”,
present in session "Landslide risk assessment and management" of the Second World Landslide
Forum.