How can we measure the impacts of public prevention

Multidisciplinary Research on Geographical Information in Europe and Beyond
Proceedings of the AGILE'2012 International Conference on Geographic Information Science, Avignon, April, 24-27, 2012
ISBN: 978-90-816960-0-5
Editors: Jérôme Gensel, Didier Josselin and Danny Vandenbroucke
How can we measure the impacts of public prevention policies on
urbanization in flooded areas? Methodological experimentations on the
basin of L’Ouvèze (Vaucluse, Southern-France)
Johnny Douvinet and Aurélie Lacombe
University of Avignon / UMR ESPACE 6012 CNRS
74 rue Louis Pasteur, Case 17
Avignon, France
[email protected]
Abstract
We discuss in this poster a useful methodology to assess the degree to which local authorities are authorizing construction in areas liable
to flooding. This study is carried out on the basin of L’Ouvèze (280km²), located in the south of France (Vaucluse), because a severe flash
flood occurred the 1992, September 22th, inducing dramatic (32 victims) and expensive (more than 2M€) damage. After this event, several
tools have been proposed by risk managers and the department to reduce vulnerability of societies and to stop urbanization in the major bed
of the river, l’Ouvèze. Therefore, 20 years after this event and despite the tools supported during the last decade, 19 % of new constructions
have been authorized in areas prone to flooding (1990-2010), and several municipalities totally neglect this inundation risk.
Keywords: flooded areas, urbanization, indicators, impacts of public politics, Ouvèze.
1
Introduction
Construction in areas prone to flooding becomes an increasing
problem in France due to industrial, residential, financial and
individual pressures [1, 2, 3, 4]. Urban planning is subject to
the interests of capital and local communities, and agriculture
suffers blind destruction by urbanization of the highest quality
farmland that produce food in future crisis periods whereas at
the same time placing ever greater demands on limited natural
resource [5]. On the other hand, the ever-increasing pressures
from investment and construction in flooded areas show no
regard for the threat of future floods and natural hazards [6].
To regulate the increase of new construction in dangerous
areas, and since the severe 1988, 1987 and 1992 flash floods,
the French government created since 1995, July, the “plans of
risk prevention” (through the Barnier Law), especially to face
to flooding. This plan is of great importance as it defines areas
where it is possible (or not) to build new constructions taking
into account natural hazard and its velocity. Therefore, despite
a strong legislation, several municipalities do no approve such
documents: in 2011, if 7.191 plans have been validated and if
3.100 plans remain in course, they might be present on 16.314
municipalities and on 300 cities grouping 2 M. habitants [7].
This lack of respect for the legislation is unacceptable from
the viewpoint of sustainable development or of environmental
ethics [5]. Nowadays, we can find in France hundreds of cases
of legalized new construction of residential, business or other
buildings in flooded areas. One recent study led by the ORIG,
Observatoire du Risque Inondation dans le Gard [8, 1] shows
that 100.000 houses have been built in flooded areas in France
over the period 1999-2008, especially in the south of France.
The events occurred in 2010 (53 victims in February, 28th, and
26 due to the Narturby flooding in June, 15th) also reveal that
population is not aware of risk or danger, and they do not have
the good behaviors to face to flood [9].
Thus, in this study, we propose a few indicators to measure
the impacts of public politics on land use and urbanization in
flooded areas. We test these parameters on the Ouvèze basin
(figure 1) as a severe flash flood occurred in 1992, September,
22th, inducing dramatic (32 victims) and expensive (more than
2M€). Many studies have been carried out on this basin by the
local risk managers since 1992 and these efforts strongly help
the French government (especially in the creation of the plan
of risk prevention in 1995). Since the 1992 event, we attempt
a decrease of urbanization in flooded areas but the reality may
be quite different as the plan of risk prevention was approved
in 2006, so 14 years after the 1992 event. Over this period and
even after, a few constructions have been built in the damaged
flooded areas. Consequently, we test various indicators to see
what communities are taking into account natural hazards, and
those that pursue their development in dangerous areas.
2
Indicators and methodogical discussions
The evaluation of public prevention policies is considered as a
tool to re-evaluate the place of local actors and to improve the
information delivered by stakeholders and mayor-elects [6].
Such evaluation permits to underline the gaps between initial
objectives and those really obtained [10]. In order to better
assess the efficiency of flooding risk prevention, specific tools
appear since the two last decades [11]. Restrictions especially
concern land planning. Thus, approaches focus on the nature
of land rules and on the consequences of plans of prevention
in comparing also the number of buildings in flooded areas. If
new constructions are authorized in risk areas, while spatial
constraints exist, public politics do not play a key role at local
scales. On the other hand, whereas in UK Benefices and Costs
Approach (BCA) approaches are current, in France, it remains
poorly satisfying for various reasons [12]: a gentle interest for
public financial partner; a lack of data and of the significance
of synthetic indexes on which such approach arrive. Hence, in
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AGILE 2012 – Avignon, April 24-27, 2012
Figure 1: Location of the 23 studied communities in the Ouvèze basin (Vaucluse, in Southern France) and results
obtained with the “risk decision index” (number of houses divided by the flooded area) over the period 1980-2010
front of important limits of economic and synthetic studies,
we decided to research another tool for measuring the impacts
of public prevention politics on urbanization in flooded areas.
2.1
Classical indicators: measuring urban sprawl
and potentially exposed population
A map can firstly be proposed at a parcel scale to evaluate and
follow urban sprawl through different periods [2, 3, 6]. On the
Ouzève basin, this work was yet realized by the DDT-84 (the
Direction Départementale des Territoires du Vaucluse) for the
period 1945-2010, thanks to the paper and numerical sources
supported by IGN (Institut National Géographique). This map
underlines that the increase of urbanized areas (private houses,
public constructions) was stronger on the communities located
in upstream basin as well as for Vaison-la-Romaine and Roaix
on which many houses were legislated in flooded areas (figure
1). Therefore, the dates of constructions with this map remain
unknown. Complementary, a second work was led in 2005 to
quantify the population in flooded areas. On each parcel, the
population was calculated thanks to the data base from INSEE
(Institut National Statistiques) and government can now have
an idea of the number of people located in flooded areas.
2.2
Detecting territories where mayor-elects have
difficulties to apply the flood risk prevention
Even if these works give satisfying results, we decided to
create other indicators to define the degree of liberty a mayorelects has regarding the size of flooded areas on its territory.
The Flooded Area by Municipality (FAM) is first compared to
the number of houses built over the period 1980-2010 to have
one index on their risk decision. Several municipalities appear
constraints on their development but they respect restrictions,
as Jonquières or Bédarrides (figure 1). At the opposite, we can
observe constructions in flooded areas while the latter present
a small size as on Roaix. Consequently, houses are condensed
in a small risk area and this index reveals that communities do
not arrive to apply flooding prevention. The problem becomes
more complex when many houses are present in large surfaces
(as for Vaison-la-Romaine). Indeed, this scale effect decreases
the value for risk decision indexes (figure 1). A second index
was proposed to evaluate the average population exposed in
flooded areas for each community (using the average number
of 2.3 people present for one house), but we cannot make the
differences between resident and working population [14].
2.3
Calculating the number of new constructions
authorized in the different flooded areas
The number of houses was also counted in taking into account
the different flooded areas from which support the restrictions
defined in the plan of risk prevention. The risk decision index
is improved here and we precise the previous approach as few
municipalities can build constructions in areas where flooding
risk is not frequent and the most dangerous for the population.
Normally, in the original plans of risk prevention, two colors
were distinguished: red areas forbid new hoses, and blue areas
render necessary to adapt new constructions to future floods.
But adjustments are observed since ten years [1]. Now we can
observe other colors as orange, yellow and green according to
the water-levels and the velocity of flows. Difficulties for the
government to force communities to have their own plans of
prevention explain this multiplication of colors and different
type of adaptations. The purple color also appears in order to
permit buildings in recurrent flooded areas in respect with the
condition that communities promise flooding arrangement [1].
When we dress the state-of-the-art of the Ouvèze basin (table
1), it is clear that a few municipalities authorize constructions
in areas where hazards are not frequent (green or yellow), but
those where index becomes higher in orange or red areas take
a risk if population is not informed (as Violès and Roaix).
Multidisciplinary Research on Geographical Information in Europe and Beyond
Proceedings of the AGILE'2012 International Conference on Geographic Information Science, Avignon, April, 24-27, 2012
ISBN: 978-90-816960-0-5
Editors: Jérôme Gensel, Didier Josselin and Danny Vandenbroucke
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AGILE 2012 – Avignon, April 24-27, 2012
Table 1: Number of houses built in the different flooded areas 1) before 1990; 2) over the period 1990-2010
Name of the studied
communities
Houses locted
Orange
Hatched
in red areas
areas
orange
1
2
1
2
1
2
Beaumont-du-Ventoux
0
0
0
0
0
1
Bédarrides
459
57
68
11
0
0
Brantes
2
0
1
0
0
0
Courthézon
58
10
0
0
88 26
Crestet
3
2
3
1
0
0
Entrechaux
2
6
1
3
0
0
Faucon
0
1
0
0
0
0
Gigondas
2
0
0
0
0
0
Jonquières
51
33
2
10
341 239
Malaucène
20
5
26
6
0
0
Puyméras
2
2
5
1
0
0
Rasteau
1
2
0
0
0
0
Roaix
1
3
0
10
0
0
Sablet
0
1
0
0
0
0
St-Léger du Ventoux
4
0
2
0
0
0
St-Marcellin lès Vaison
3
0
3
0
0
0
St-Romain en Viennois
2
3
5
0
0
0
Savoillan
2
4
3
5
0
0
Séguret
0
0
0
1
0
0
Sorgues
42
11
24
8
0
0
Vacqueyras
0
0
0
0
0
0
Vaison-la-Romaine
27
13
32
8
0
0
Violès
18
43
0
2
42
52
Source: BD TOPO © IGN 1990, 1995, 2000, 2005 and 2010; DDT-84.
2.4
Considerating the land use pressure
In link with the degree of liberty of mayor-elects, we want to
know the number of new houses built in non-flooded areas to
evaluate the land use pressures that communities undergo. If a
little number of houses is build in flooded areas (< 20%), we
can consider that communities play the role of risk prevention.
This indicator calculated for example on the period 2000-2010
gives the following results: 814 and 196 constructions appear
out and in flooded areas; while 422 and 392 houses happened
over the period 2000-2005 and 2005-2010 (hence the land use
pressure does not decrease), the number of constructions in
flooded areas is ranging from 70 to 126. Differences between
communities are important: Vaison-la-Romaine or Roaix have
good results, at the opposite of Jonquières or Violès (figure 3).
Indeed, the latter deliver numerous buildings permits in risk
areas while the land use pressure is not important. With the
table 1 and the figure 2, initial information is really improved.
2.5
Linking constraints of plans of risk prevention
with the spatial land plannings
Another (but not least!) index leads in comparing the numbers
of areas in plans of risk prevention and in plans of land use. In
France, a lot of conflicts are due to these two documents as
the plans of land use were created in 1967 whereas plans of
risk prevention are not always approved. On the Ouvèze basin
urban areas are ranging from 268 in 1999 to 314 in 2008, just
in surfaces presenting sensitivity to flooding in plans of risk.
Yellow
areas
1
2
0
0
20
5
0
0
148 33
0
0
0
0
0
0
0
0
24 10
16 10
0
4
0
0
2
0
5
7
0
0
0
0
0
0
1
1
0
0
4
0
0
0
76 44
47 78
Green
areas
1
2
0
0
0
0
0
0
10
2
0
0
0
0
0
0
0
0
137 65
0
0
0
0
0
0
23 28
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
12
4
0
1
Total houses in
flooded areas
1
2
1+2
0
1
1
550
71 621
3
0
3
305 71 375
6
3
9
3
9
12
0
1
1
2
0
2
565 357 912
62
21
83
7
7
14
1
2
3
26
41 67
5
8
13
6
0
6
6
0
6
7
3
10
6
10
16
0
1
1
70 20
90
0
0
0
147
69 216
107 176 283
Urban surfaces strongly increase in a few years in Vaisonla-Romaine (+22), Jonquières (+17) and Violès (+12) whereas
other communities reduce their urban surfaces (figure 2). Such
results might reveal perverse planning strategies: mayor-elects
can open new areas for buildings in plans of land use while in
plans of risk prevention, such adaptation remains illegal.
3
Results and perspectives
This article presents the methodology framework we discuss
and we test on the Ouvèze basin to measure all the impacts of
public prevention politics on urbanization in flooded areas. If
several communities play the role of risk prevention, others do
not take into account the flooding risk. On the communities of
Jonquières or Violès, citizens are exposed to flooding hazards
(without automatically knowing it) and vulnerability increases
while the plans of risk prevention should limit it. This study
also underline that a few mayor-elects have a lot of difficulties
to regulate land use pressures. On the point of methodological
overview, all these indexes show different things and we have
to use all of them without looking for a synthetic indicator.
Acknowledgments
The authors thank P. Alligier, P. Barillet, S. Lamrani and P.
Lusa (DDT-84) for data and all the comments provided during
this study. We also would like to thank A. Richaud and C.
Genre-Grandpierre for theirs advises.
Multidisciplinary Research on Geographical Information in Europe and Beyond
Proceedings of the AGILE'2012 International Conference on Geographic Information Science, Avignon, April, 24-27, 2012
ISBN: 978-90-816960-0-5
Editors: Jérôme Gensel, Didier Josselin and Danny Vandenbroucke
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AGILE 2012 – Avignon, April 24-27, 2012
Figure 2: Number of new constructions authorized in flooded areas and its percent in comparison with total
urbanization registered over the period 2000-2010.
References
[1] J. Douvinet, S. Defossez, A. Anselle, A.-S. Denolle. Les
maires face au Plan de Prévention du Risque Inondation
(PPRI). L’espace géographique, 1, 31-46, 2011.
[2] J. Dubois-Maury. Les risques naturels en France, entre
réglementation spatiale et solidarité de l’indemnisation.
Annales de géographie, 627-628, 637-651, 2002.
[3] S. Beucher, S. Rode. L’aménagement des territoires face
aux inondations : regards croisés sur la Loire moyenne et
le Val-de-Marne. Mappemonde, 94, 2009.
[4] B. Ledoux. La gestion du risque inondation. Editions
Lavoisier, Paris, 770 p., 2006.
[5] Waheed A.A., Chucwuemeka A.J.. Modeling the impacts
of urbanization on river flooding using the St-Venant
equations. Journal of Engineering and Applied Sciences,
5 (7), 46-56, 2010.
[6] R. Laganier. Recherche sur l’interface eau et territoire
dans le Nord de la France. Mémoire d’habilitation à
diriger des recherches, Lille, 2 vol., 250 p., 170 p, 2002.
[7] Mission Risques Naturels. Evaluation de la contribution
des Plans de Prévention des Risques Naturels (PPRN) à
la réduction de la vulnérabilité collective et individuelle.
Rapport de synthèse, Paris, 29 p, 2009.
pertinence et de l’efficacité des PPRN. Actes du
troisième colloque «Géographes et assureurs face aux
risques naturels sur l’évaluation des politiques publiques
de prévention. Paris : MAIF-Université de Paris Diderot
7, p. 155-175, 2008.
[9] F. Vinet, L. Boissier, S. Defossez. La mortalité comme
expression de la vulnérabilité humaine face aux
catastrophes naturelles : deux inondations récentes en
France (Xynthia, var, 2010). Vertigo, 11, 2, 2011.
[10] B. Barraqué. Assessing the efficiency of Economic
Instruments : Reforming the French Agences de l’Eau.
Politics and Institutions, 2, 215-230. 2000.
[11] G. Bouleau. Légitimité des indicateurs et de l’évaluation
des politiques publiques. Quelques exemples dans la
gestion de l’eau, Rapport interne Cemagref, 18 p., 2007.
[12] K. Erdlenbruch, E. Gilbert, F. Grelot, C. Lescoulier. Une
analyse coût-bénéfice spatialisée de la protection contre
les inondations. Application de la méthode des
dommages évités à la basse vallée de l’Orb. 18p.
Ingénieries, 53, 2008.
[14] C. Terrier, M. Sylvander, A. Khiati. En haute saison
touristique, la population présente double dans certains
départements, Rapport Interne INSEE, 6 p., 2010.
[8] S. Gérin, C. Jajji. Développement d’indicateurs de la
vulnérabilité collective aux risques naturels à l’échelle de
la commune, en vue d’une méthode d’évaluation de la
Multidisciplinary Research on Geographical Information in Europe and Beyond
Proceedings of the AGILE'2012 International Conference on Geographic Information Science, Avignon, April, 24-27, 2012
ISBN: 978-90-816960-0-5
Editors: Jérôme Gensel, Didier Josselin and Danny Vandenbroucke
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