Réduction de la vulnérabilité au risque inondation : l’exemple du Palais de Justice de Paris

Reducing vulnerability to flood risk: The example of Paris’courthouse

¹ ISL Ingénierie, 75 boulevard Mac Donald, 75019 CARQUEFOU CEDEX
emails : savatier@isl.fr, salembier@isl.fr
² Cap Ingélec, La Fleuriaye, 1 rue Alessandro Volta – BP 30765 – 44481 Créteil Cedex
email : l.monnier@capingelec.com
³ Service Immobilier du Palais de Justice (Cour d’Appel), 34, quai des Orfèvres, 75055 PARIS Louvre SP
email : Paul.Gillot@justice.gouv.fr

Résumé

Le diagnostic du risque inondation du Palais de Justice de Paris, situé sur l’île de la Cité, met en évidence qu’il est soumis à un aléa par infiltration depuis la nappe pour les crues supérieures ou égales à celle de 1982 (crue décennale).

La vulnérable du Palais de Justice est importante mais relativement récente car les installations techniques ont été transférées au sous-sol à partir des années 1960 et principalement après 1995. La configuration actuelle n’a donc pas connu l’épreuve d’une crue importante.

Les possibilités techniques de réduction de la vulnérabilité ont été analysées et des aménagements visant à assurer le fonctionnement en mode dégradé en période de crue et post crue ont été définis et sont actuellement en cours de réalisation. Ces aménagements comprennent le transfert des installations essentielles et l’adaptation des installations électriques afin de permettre l’alimentation d’une partie du site par des groupes électrogènes.

Abstract

The flood risk assessment of Paris’courthouse, located on ‘la Cité’ island, highlights that the underground and ground floor are undergoing flood hazard by groundwater seeping for floods equal or greater than the one of 1982 (10 years return period) and especially for 1955-like floods (50 years return period, generalized flood of the underground floor) and 1910-like floods (100 years return period, flood over most of the ground floor). The flood durations may be important, with for instance about 10 days on the ground floor for the 1910’s flood.

Paris’courthouse vulnerability is high but fairly recent since almost all the technical equipment has been displaced to the underground floor since 1962 and above all after 1995. The courthouse has therefore not known any major flood in its current configuration. For a flood like the ones of 1955 or 1910, all the technical equipment would be severely affected and the courthouse would be out of service during the flood and until the equipment is repaired or replaced (probable duration of several weeks). The costs of the technical damages are estimated at 11,5 M€ (except the costs due to the long-lasting interruption of the courthouse service and the loss of the archives, that could not be estimated).

Vulnerability reduction by transfer of all the technical equipment to unflooded areas or by constructing waterproof casing around the equipment is not possible due to the lack of available space in the unflooded areas and to the narrowness of the technical premises.

The courthouse has therefore chosen to reduce vulnerability by adapting the technical equipment in order to be able to maintain deteriorated service during the flood, to facilitate the return to normal state and to reduce the damages. The adaptations include the transfer of essential equipment to available unflooded areas and modifications to the electricity network and devices aiming at separating flooded and unflooded parts and being able to supply a part of the building with electricity-generators.