There are three
main scales at which evacuation models are employed for
flood
event management as follows:
- Micro – This
corresponds to a scale
where each
individual receptor at risk (e.g. person, vehicle or property) is
modelled and
there is a detailed representation of the evacuation routes. A complex
modelling system
(e.g. an
agent-based model) is often used to estimate the evacuation times for
each
individual receptor;
- Meso – This
corresponds to a scale
that is
between a micro and macro-scale. In
meso
models the receptors are lumped together. The evacuation time is
estimated by
assessing the demand for and the capacity
of the evacuation routes, which are evaluated on a geographical basis;
- Macro – In a macro
model the
receptors are also lumped together. The
estimates of the evacuation
times are based purely on the distance to the exit of the at risk
area, the capacity of the route and the average evacuation speed. A
macro scale model is often
used to provide
an initial estimate of the evacuation time for a large area. (e.g. at a
regional scale).
The
distinction between micro, meso and macro scale evacuation models and
the
typical scales at which they are applied is shown in Figure 1.
The
type of
evacuation model that is appropriate for a particular flood risk area
will
depend on the level of risk and the processes
which the evacuation modelling is
seeking to inform. A
densely populated urban
area where the scale of potential evacuation is large may require a
detailed
simulation model where the traffic and flood hazard is modelled in a
truly dynamic
way. Other
issues that need addressing are:
- An understanding
of the level of congestion
delay, that is inevitable under even the most
effective traffic management schemes, and
- The
level of spontaneous evacuation that may occur in advance of an
official
evacuation warning.
Figure 1: Micro, meso and macro
scale
evacuation model
with the suggested scale
of their application.
Different
evacuation models were tested in the different pilot sites and at
different scales as shown in the following table:
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