Titolo del lavoro

Flood Evacuation Plan as Support
for Flood Disasters Management
S. Frongia1 and G.M. Sechi2
XXXV CONVEGNO NAZIONALE DI IDRAULICA
E COSTRUZIONI IDRAULICHE
Bologna, 14-16 Settembre 2016
1
2
4
1DICAAR
Dept. of Civil and Environmental Engineering and ArchitectureUniversity of Cagliari, frongiasara@tiscali.it
2DICAAR Dept. of Civil and Environmental Engineering and ArchitectureUniversity of Cagliari, sechi@unica.it
21-0216
Flooding events are affecting with increasing frequency Mediterranean region where large amounts of people every
year are under flood-risk and growing damages are waited in the future. Precipitation events are triggered by
cyclone circulation patterns determining flash floods, as happened in Sardinia (Italy) the 19th November 2013 when
Cleopatra Cyclone hits mainly the Eastern coast of the regional territory with rainfall of 440 mm gauged in less
than 24 hours and causing a death toll of 13 (among children, adults and elderly). The massive damages have been
appreciated around 60 M € only in Olbia town, in the North-East of the island, and more villages, roads, bridges,
agricultural and touristic areas have been seriously damaged in the South and North Eastern part of the territory.
The increasing urbanization requires disaster management plans, necessary for preparation, support and
reconstruction when natural or man-made disasters occur and at this step the Flood Hazard Maps and Flood Risk
Maps should be supported by an accurate flood evacuation plan during emergency situations in order to direct
people towards proper evacuation path reaching specified safe heaven. Recent major flood events around the world
have highlighted the importance of an effective emergency response in minimising loss of life and optimising the
resources available (Lumbroso, 2011). Whether to implement a mass evacuation of people from an area at risk of
flooding can be a major issue for emergency managers, the modelling of the evacuation process generated by a
forecast flood is important for those responsible for the efficient and safe movement of people during evacuations
(Lumbroso et al., 2010). Evacuation modelling could predict “bottlenecks” in the system before they are
experienced, it could also be used to determine the impact of road closure due to flooding and the impact of phased
evacuation scenarios can lead to establishment of appropriate evacuation policies and shelters strategies.
The case study illustrates a flood evacuation plan developed for a pilot basin of the Sardinian Flood Risk
Management Plan: the Coghinas River lowland valley basin, Figure 1. The developed flood evacuation plan for the
pilot basin allows to plan a proper emergency management situation defining accurately safe heaven location areas,
according with the Alert Operating Instructions given by the Civil Protection Agency, AOICP (Sardinian Region,
2015), allowing to evaluate flood damage in terms of tangible damage (building collapse and loss of vehicles) and
intangible damages (death toll).
The HR Wallingford software, RFSM_EDA and Life Safety Model (LSM), have been applied to reproduce the
water depth and velocity development in the territory and, herein, the simulation results are shown for the flood
evacuation plan defined considering a potential catastrophic event of 200 years of return-time period on the pilot
basin.
The Coghinas river lowland valley basin is managed by four towns: Viddalba, Santa Maria Coghinas, Valledoria
and Badesi. The area is interested by a distribution of 3372 structures where 9450 persons have been allocated
taking in consideration a future demographic increment, between residents and tourists, and in addition the Road
Network has been defined in detailed aiming to simulate a itemized model. The flood evacuation is controlled by
the Authorities through Warning Centres located in the Casteldoria Dam Control Building and the Council offices
of Viddalba an Valledoria and by Events as critical road points closure, Figure 2.
The flood event is characterised by a base time of 23 hours with the peak of the event at 9 hours from its beginning.
The scenario has been run different time considering a delay in the evacuation of 20 minutes between two
consecutive simulations. LSM models the flood evacuation considering the mobilization of the PARU, Person at
Risk Unit, located inside 500 m from the flood maximum extension, as shown by the red boundaries in Figure 3,
and focusing the attention on the loss of life damage. In fact, LSM shows and describes PARU conditions and how
they could perish, Table 1.
In addition, the analysis of the whole simulations allows to define the loss of life curve where the potential death
toll is interconnected with the warning time issuance. The loss of life curve shows up as relevant support tool for
the Civil Protection Agency in order to identify when the evacuation warning should be sent or when should be
better leave the people decide how to act avoiding higher damages, Figure 4.
3
1
POPULATION AT RISK UNIT (PARU)
Scenarios
Warning time prior Warning time prior
No
at 6 h to the peak of at 9 h to the peak
Warning
the event
of the event
N°of Parus
Unaware
Aware
Aware&Evacuating:
Safe
Toppled
N°Deceased-Total
N°Deceased-Drowned
N°Deceased-Exhaustion
(PPC<PPCC)
9450
8334
2
0
308
0
806
274
9450
0
2918
0
6498
0
34
0
9450
0
0
0
9450
0
0
0
235
34
0
N°Deceased-BLDG Collapse
N°Deceased-Drowned in
BLDG
N°Deceased-VHCL Toppled
196
0
0
95
6
0
0
0
0