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Technical Committee 307 /
Comité technique 307
determine the run-off conditions, the precipitation and the
amount of available soil material. A classification is made and
the results of the mapping and classification are reported on a
map.
A
mapping for coastal areas
can also be performed. The
hazards are identified by evaluation of the present state of the
coast and a coastal geomorphologic model can be established.
This includes the geomorphology, the topography and
bathymetry as well as the driving forces such as water levels,
waves, water currents and existing coastal protection. With
climate change scenario for the chosen time period the
probability for hazards such as erosion, landslides and flooding
can be estimated. In Sweden, an overview mapping of the
prerequisites of coastal erosion of the Swedish coasts, larger
lakes and rivers has been carried out by SGI and maps will be
found at [16] A model for risk analysis has also been developed
at SGI, based on the principle of carry out analysis step by step
depending on the need for decision basis [14] In many countries
there are on-going works with
inundation mapping
due to EU
directive. In many cases the mapping is done only for today’s
climate, but it is important to complement it with climate
change scenarios.
3.2 Consequences
Potential consequences of a natural hazard can be described on
overview or detailed levels. Within a governmental
investigation on slope stability in the Göta River, SGI has
developed a detailed method to identify, map and when possible
assess consequences of potential landslides throughout the
studied area [15, 16].
The method comprises:
identification of consequences
inventory/mapping of objects that may be affected
assessment of the vulnerability, ie the probability of a
certain consequence in case of a landslide
method for monetary assessment
Relevant factors to consider are e.g. population, property,
contaminated land, transportation network, industry. Monetary
valuation of the consequences and estimation of the
vulnerability are performed. The work has been divided in
societal consequence sectors: buildings; transport, exposure,
vulnerability and life; environmentally hazardous activities and
contaminated sites; water and sewage systems; nature; culture;
energy and electric supply systems; trade and industry.
The consequence is set to be the product of the inventory of
elements at risk, value per unit area, the vulnerability and the
exposure. The result is presented in a 2D map with five
consequence classes given in MSEK/ha.
3.3 Potential risk areas
The principle is to identify risk areas based on the probability of
an event and the consequences of such an event. Depending on
the need of information risk analysis can be carried out on
overview or detailed levels. In the Göta River investigation five
classes of probability and consequence, respectively, are
combined in a risk matrix from which three classes of risk are
identified (Figure 2);
low risk level
medium risk level (investigation required)
high risk level (preventive measures are required).
The outcome of the risk analysis can be presented in maps
covering the investigation area illustrating the extent of the
three risk levels. The method has been used in practice in e.g.
the Göta river valley [17].
Figure 2. Illustration of risk analysis, where the consequences and
probabilities for landslide are grouped into 5 classes and combined by
GIS techniques in a risk matrix with three risk classes; low risk level,
medium risk level (investigation required), high risk level [17].
3.4 Strategies and alternative measures
At the local level both for spatial planning and the built
environment, the need for mitigation and adaptive measures
must be identified, and data for the design and construction of
such measures must be clarified. Requirements for remedial
works can also be predicted using field-monitoring data, which
may change the risk management philosophy from a reactive to
a more pro-active one.
Mitigation measures for landslides, erosion and flooding
risks often require levees, coastal protection and/or other
stabilising measures. Such measures require geotechnical
information during several stages of the planning and building
process. In spatial planning, all factors that may cause risk for
health and safety must be identified so that buildings and
infrastructure will be located outside present and future risk
areas or measures taken to secure these risk areas.
3.5 Socio-economic analyses and environmental impacts
For possible measures in spatial planning or for adaptation of
the built environment socio-economic analyses are carried out.
When socio-economic analyses are made they have to be based
on correct actual data and valid methods to predict future
development for different alternatives/scenarios. This is the
basis for establishing the risk level that needs to be related to the
acceptable risk level, the need of, and which, countermeasures
that can be used to alleviate the potential problems. Also the
stakeholders must be identified and the activities that are
affected by possible changes to the land or coastal area.
Analysis can be done for example by a Cost-Benefit Analysis
(CBA). The basic way of working with a CBA model is to start
by estimating total damage and loss for the “Do Nothing”-
alternative. This value is later used as the benefit (or avoided
damage) for the investigated options of preventive actions. The
next step is to estimate the schedule and cost of implementing
the options. Finally, if there still is a risk of damages for the
investigated options; the cost of this is also calculated. For a
CBA the selection criterion is that if the ratio between benefits
and costs is greater than 1 (benefits divided by costs >1) the
option is worth doing. The option with the highest benefit cost
ratio gives “best value for money” [18].
Most of measures to reduce risks for natural hazards have to
be built in environmentally and naturally sensitive areas close to
the sea or rivers, in some cases consisting of Natura 200 areas.
For that reason, all measures have to be evaluated due to the
environmental impacts. For the proposed strategies and
alternative measurements environmental consequences have to
be considered.
3.6 Basis for spatial planning and adaptation
For spatial planning, following the stages in the model, the
decision makers will have a proper and transparent basis for
discussion with different stakeholders and the final decision of
