Sort by *
18 November 2022
Public thematic report
In the Seine basin, flooding is one of the biggest natural hazards, after drought.
The Île-de-
France metropolitan area is particularly vulnerable to the risk of flooding. The last major
floods occurred in May-June 2016 and January-February 2018, costing €1.4 billion and €150
million to €200 million respectively. According to a recent OECD assessment, a 100-year
flood reaching the maximum level of the 1910 flood (8.60 metres at the Austerlitz bridge)
would cause direct damage totalling around €30 billion. However, the insufficient
consideration of this risk by the population and by local government has resulted in a
deficient prevention strategy, notably due to poor coordination. The report published today,
drawn up by a joint panel of the Court of Accounts and the Île-de-France Regional Audit
Chamber, assesses the state of awareness of the risk linked to a 100-year flood of the Seine
river, as well as the objectives set and the financial means deployed to prevent this risk. It
also examines the effectiveness and efficiency of action taken to reduce this risk. Finally, it
analyses the extent to which the governance and sustainable management strategy for the
Seine river have contributed to flood risk prevention in recent years.
A major risk and severity insufficiently taken into account
Many maps covering overflow flooding are available to the general public through flood risk
prevention plans (PPRI) and on dedicated websites (such as "Cartoviz - potential flood zones")
However, floods caused by rising groundwater and runoff are more difficult to assess - even
though runoff accounts for about one third of insured damage in the Île-de-France region.
Central government must ensure that all stakeholders (citizens, companies, administrations)
have access to the information available on this risk, particularly on flooding by rising
groundwater. The Court also recommends increasing awareness and regularly checking the
perception of this risk among the population of Île-de-France. Local authorities have not set
quantified damage reduction targets and have made little use of the major natural risk
prevention fund for the Île-de-France region: from 2009 to 2021, the cumulative amount of its
commitments amounted to €65 million and its expenditure totalled €23 million, well below the
expenditure of other regions affected by flood risk.
Action to reduce the risk of flooding is still limited
The Paris conurbation is much less protected against major floods than other international
cities: the theoretical level of protection concerns a return period for a flood event of 30-50
years for the inner suburbs, 10-20 years between the Pont d'Iéna and Issy-les-Moulineaux, and
100 years for the rest of Paris. In comparison, London is protected against a 1,000-year flood
return period and is aiming for protection for a return period of 10,000 years by 2100. Various
means have been put in place to deal with these risks: major investments in upgrading dykes
and walls covering 120 km (taken over with difficulty by the Greater Paris Metropolitan
Authority) and the completion of the La Bassée retention basin project, intended to strengthen
protection upstream of Paris, the preservation and restoration of floodplains, the regulation of
urban development in at-risk areas and the design of resilient housing. However, the Court
warns of the disparate preparation by the operators of infrastructure networks likely to be
exposed (electricity, gas, telecommunications, digital network, transport, heating, drinking
water, sanitation), as well as the absence of action by the region to help small and medium-
sized enterprises reduce their vulnerability. Finally, it emphasises that an insufficient number
of initiatives have been implemented to protect cultural heritage in Île-de-France.
Absence of a coordinated strategy for the Seine river basin
Île-de-France is part of the Seine river basin. It is at this level that central government, local
government and all stakeholders (infrastructure network operators, non-profit organisations,
companies, insurers) must coordinate their efforts with a view to effectively managing risk
prevention. However, this coordination is currently insufficient. The 2007-2013 Seine plan has
not gained effective support from the various stakeholders, particularly the regions (except for
Grand Est), for a shared vision of the river and common objectives - unlike the Loire and Rhône-
Saône plans. For example, there is no working forum on topics relating to the risk of flooding
of the Seine like the "stakeholder forums" organised in the Loire and Rhône basins. However,
the dispersion of action and stakeholders is contrary to the principle of solidarity, which is
supposed to be the cornerstone of the national flood risk strategy, and which aims to share
responsibilities and efforts to reduce the negative consequences of flooding fairly between all
territories and stakeholders: upstream-downstream, urban-rural, right bank-left bank.
Accordingly, the Court recommends that central government and the competent local
government authorities report annually on the status of the flood risk prevention policy by
bringing together representatives of all stakeholders.
Read the report
Julie Poissier
Head of Press Relations
+33 (0)1 42 98 97 43
+33 (0)6 87 36 52 21
Court of Accounts
Court of Accounts