risk management - monitor ii

16 Monitor II Floods and landslides
Monitor II Hazard maps 17
Debris flow
Source area
Main track
Depostional area
Figure 13: Landslides – flows (courtesy USGS).
Creep
Earth flow
Debris avalanche
Lateral spread
also commonly mobilize from other types of
landslides that occur on steep slopes, are nearly
saturated, and consist of a large proportion
of silt- and sand-sized material. Debris-flow
source areas are often associated with steep
gullies, and debris-flow deposits are usually
indicated by the presence of debris fans at
the mouths of gullies. A debris avalanche is a
variety of very rapid to extremely rapid debris
flow. Earthflows have a characteristic
”hourglass” shape. The slope material liquefies
and runs out, forming a bowl or depression
at the head. The flow itself is elongate and
usually occurs in fine-grained materials or
clay-bearing rocks on moderate slopes and
under saturated conditions. A mudflow is an
earthflow consisting of material that is wet
enough to flow rapidly and that contains at
least 50 percent sand-, silt-, and clay-sized
particles.
Landslide – creep, lateral spread
Creep is the imperceptibly slow, steady, downward
movement of slope-forming soil or rock.
Movement is caused by shear stress sufficient
to produce permanent deformation, but too
small to produce shear failure. Creep
is indicated by curved tree trunks, bent fences
or retaining walls, tilted poles or fences, and
small soil ripples or ridges. Lateral spreads are
distinctive because they usually occur on very
gentle slopes or flat terrain. The dominant
mode of movement is lateral extension
accompanied by shear or tensile fractures.
The failure is caused by liquefaction, the
process whereby saturated, loose, cohesion less
sediments (usually sands and silts) are
transformed from a solid into a liquefied state.
The tools: state-of-the-art
A major goal of the MONITOR II project is to contribute to the definition of a harmonised
methodology for hazard mapping and contingency planning within the EU-member states, based
on the experiences of the organisations participating in MONITOR II. Based on the state-of-the-art
analysis and evaluation of hazard mapping and contingency planning practices prevailing in the
participating countries and organisations, recommendations for improvement, harmonisation and
adaptation of existing hazard maps and contingency plans were worked out.
Be informed – hazard maps
The process of hazard assessment
Starting point of hazard assessment is a
situation of threat, for which hazard assessment
is a recommended (or in some cases:
a legally prescribed) measure. The goal of
hazard assessment is to define hazard potential
(qualitative as well as quantitative).
Activities in hazard assessment execution
are carried out according to methods (rules,
guidelines, practice…). These methods can be
seen as a knowledge source for successfully
reaching the goal defined for a plan. Subplans
of hazard assessment are hazard inventory,
hazard analysis and hazard evaluation with
each having a related goal.
Hazard maps can generally be described as
a major output of hazard assessment and
constitute a decisive element in risk management.
They assist the identification, evaluation
and reduction of risk by using an optimal
combination of measures. In a general
definition the term hazard map encompasses
both the map proper and all the expertise.
Hazard assessment thus covers hazard
inventory AND hazard analysis AND hazard
evaluation.
Hazard inventory: Is the identification and
description of existing and potential hazards
and the general conditions (physical –
meteorological - ....) that determine them.
Tilted pole
Soil ripples
Bedrock
Firm clay
Hazard analysis: Is the (qualitative, semiqualitative
or quantitative) description of
the probability of the event and its spatiotemporal
location and magnitude (intensity).
This involves measurement of parameters and
estimation (by modeling approaches) and interpretation
of data.
Curved tree trunks
Fence out of alignment
Figure 14: Landslides – creep and lateral spread (courtesy USGS).
Soft clay with water-bearing
silt and sand layers
Figure 15: Hazard assessment and related goals (S. KOLLARITS et al. 2007)
Within hazard analysis one (or more) likely
scenarios of hazard process development are
being considered. They serve as the central
input to hazard evaluation.