Floods and joint risks: who pays and who benefits? (full edition)

12 May 20207 June 2020 Bertrand de Foucauld 0 Comments

In its April 3rd, 2020, article (Opening of a COVID-19 Refuge in Jouy-en-Josas (Paris Region)^[1]Available at: https://contrib.city/index.php/en/2020/04/03/opening-of-a-covid-19-refuge-in-jouy-en-josas-paris-region/), Contrib’City had mentioned, at the end of the text, that the Bas-Pré site, in Jouy-en-Josas, intended for the management of the Corona pandemic, was also flood prone. A Contrib’Citizen, whom CC thanks again, strongly questioned the website on the fact of having simultaneously mentioned two natural risks but of different priorities. CC replied that a second vulnerability, even if it could have a less urgent aspect, could increase the first. This is what happened on the night of Saturday to Sunday 10th May 2020, especially in the Ile-de-France Region where the equivalent of three weeks of precipitation fell in a few hours^[2]FRANCE 2, Intempéries : une nuit d’orages en Bretagne et en Île-de-France (Bad Weather: a Night of Thunderstorms in Brittany and Île-de-France), May 10th 2020, [Consulted on the 11th 2020]. Avaialble at: https://www.francetvinfo.fr/meteo/inondations/intemperies-une-nuit-d-orages-en-bretagne-et-en-ile-de-france_3957703.html: a flood forced Red-Cross caregivers to evacuate a nursing home in the town of Boulogne-Billancourt, during the confinement period. As a reminder, the city of Boulogne-Billancourt is located on an alluvial plain of the Seine.

The city of Boulogne-Billancourt in the hollow of a loop of the Seine, southwest of the city of Paris. Note the hills to the southwest of the river. The map faces North.

Boulogne-Billancourt. The map is oriented towards the South-West.

Boulogne-Billancourt. The 3D satellite map is oriented towards the South-West.

The Sainte-Agnès retirement home, whose cellars were flooded during the night from May 9th to 10th, 2020, is located less than 600 m from the highest known waters (bluish zone). How is it that the electrical system of an establishment receiving a potentially fragile public is installed in the most likely to be flooded level?

In Jouy-en-Josas, South-West of Boulogne-Billancourt, blades of water on the road which goes from the Loges-en-Josas village (on the southern slope) to the bottom of the Bièvre valley, took with them earth and stones showing the erosion force of this stormy flood which was however only of medium intensity.

Rue de la Liberation. On the left, the Route des Loges. In the background, the level crossing which runs along the Bièvre. One can see the alluvium on the road. Photo: BdF, May 10th, 2020, 1:08 p.m.

Front, the Route des Loges which climbs from Rue de la Liberation. One sees the earth deposited by the water that has flowed from the top of the hill. Photo: BdF, May 10th, 2020, 1:08 p.m.

Liberation Street, towards HEC Business School. On the right, an inhabitant cleans up the earth and rubble deposits. According to his testimony, these spills happen every year.

Crossroads between the Route des Loges (behind) and the Rue de la Liberation, in the background.

Floods and alluvial deposits in Jouy-en-Josas – Some residents are forced, as every year, to clean the pavement outside their home or workplace. According to the testimony of one of them, a social housing condominium, rue de la Liberation, saw its terraces and then its apartments flooded due to the fact that rehabilitation works, requested for several years, are still slow to come.

Cleaning service for the alluvial deposits, chargeable to the taxpayer. Photo BdF, May 10th, 2020, at 4:50 p.m.

If the latter had been stronger, of centennial type, one can imagine its potential damage by looking at the 1982 flood figures^[3]cf: Centre-ville de Jouy : le chantier de la polémique (Jouy City Center: the Site of Controversy), March 13th, 2020. Available at: https://contrib.city/index.php/2020/03/13/centre-ville-de-jouy-le-chantier-de-la-polemique/. If an average stormy event (but it is true that there were two thunderstorms that raged in Jouy-en-Josas, the first around 22:00 approximately, the second around midnight) could move cubic meters of rubble, what would have happened if this episode had been followed by torrential rains during several hours?

Oberkampf Street in the city center from the level crossing. Note the alluvium deposited on the road. Photo: BdF, May 10th. 12.52 p.m.

Rue Oberkampf, downtown, from the level crossing. May 10th 2020, in the morning.

Pedestrian crossing which passes under the railway. The railway line cuts Oberkampf Street and the whole town of Jouy-en-Josas.

The underground passage is flooded (about 1 meter of water height). This photo questions the relevance of the construction of underground car parks in the major riverbed. Regarding inhabitants’ security or medium-term financial management, is it reasonable to put buildings with underground levels in a flood zone? Is it fair that the taxpayers and all the insured people pay for the consequences when the inevitable eventually happens?

In the center of Jouy-en-Josas, the underground staircase that passes under the regional train C line (RER C) was flooded with a water height of about one meter. The municipality pumped the passage for several hours which, suddenly, leads one to wonder about the relevance of the construction of underground car parks in the major bed of the Bièvre. Indeed, the Nacarat site, along this river, includes underground parking lots while the building is in the middle of a flood zone (1.10 m during the flood on July 22, 1982).

Altimetric section of the Bièvre valley along an axis which runs along rue Pasteur, where the Nacarat site is located. Shifted precipitations, upstream of the river, sometimes synchronise downstream with lateral runoffs, which can be torrential given the slope of the hillsides. That rainfall synchronisation can generate a water accumulation in a given place thus leading to an exceptional flood. Diagram: BdF. Data source: IGN. *Ruisseau ou lames d’eau sur les coteaux du centre-ville de Jouy-en-Josas*: Stream or water slides on the hillsides of downtown Jouy-en-Josas. *Bief*: a reach of canal, *Crue*: Flood, *Espaces verts*: green spaces, *voies goudronnées*: roads, *voies ferrées*: railroads, *bâtiments*: buildings.

As a reminder, Jouy benefits from an exceptional living environment, is surrounded by prestigious training and research centers (X, Paris-sud, Sup-Télécoms, HEC, INRA). Its population, in particular the Val d’Albian district, is gradually passing from a working population to that of executives, liberal professions or business leaders. In short, the city is getting gentrified and the development of land is one of the signs: the price of m² has increased by 25% over the past eighteen months ^[4]CREDIT FONCIER, Prix de l’immobilier au m2 à Jouy-en-Josas (Property prices per m2 in Jouy-en -Josas). [Consulted on May 12th, 2020], available at: https://prix-immobilier.creditfoncier.fr/prix-m2/yvelines-R78/jouy-en-josas-id78322 on a fundamental uptrend since the Yvelines département^[5]Grossly, the equivalent of a UK county Real Estate mean price has more than doubled since 2000 and has increased by almost 14% since 2010 ^[6]BEST AGENTS, Évolution du prix de l’immobilier dans les Yvelines (Evolution of the price of real estate in the Yvelines), [Accessed May 12th, 2020], available at: https : //www.meilleursagents.com/prix-immobilier/jouy-en-josas-78350/. New housing construction is experiencing strong growth: in almost all of the Jouy neighborhoods, one can see building sites in operation, including in flood-prone areas.

Photo BdF, the 13th March 2020. Nacarat Construction site, on the right. On the left, less than 100 m upstream, between the trees and avenue Jean Jaurès (where we can see the two cars), flows the Bièvre which then enters a pipeline. Obviously, in the event of an exceptional flood, the water will overflow despite the dikes. In the event of a claim, who pays: the promoter or the population?

In conclusion, whether in Boulogne-Billancourt or in Jouy-en-Josas, the increase in density and demand for housing, in bourgeois Ile-de-France cities or in the process of being so, is helping to put pressure on these territories, including in places at risk. But in these risky areas (floods, landslides, pollution), who pays in the event of a disaster? Decision makers who have been warned? Or the taxpayers and the insured, that is all of us? But if the risk is assumed by the population, does the latter enjoy the profits made by these projects? If the flood hazard occurs, for example on the Nacarat site, in the center of Jouy, should it be considered as a “natural disaster” when it is, in fact, only the construction of a building without stilts, in a bathtub that can fill up at any time as soon as the weather is stormy? These are some interesting questions. Contrib’City would be interested to read the concerned people’s responses.

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