Cevennes Storm

A Cevennes episode , Cevennes storm or Cevennes rains is a particular type of Pluie which affects in particular the areas located at the foot of the the Cevennes, in the south of France and which often causes low registers Inondation S.

Departments concerned

The principal departments affected by these rains are those having part of their territory in the Cevennes:

the Ardeche,
the Gard,
the Herault,
and the Lozere.

Around, the Aude undergoes a phenomenon close with the foot to the Black Montagne. The Rhone delta and the Vaucluse are indirectly affected when the the Rhone overflows of its bed towards the east under the effect of the increased flow of its affluents of its left bank.

Unfolding

These Cevennes floods occurs if several factors are joined together:

corresponding to the characteristics of the mountain climate, from the autumnal rains or spring falls on the solid mass from the the Cevennes,
in the Languedocien plain (of the Aude to the the Rhone), a few days later fall from the typical storms of the intersaisons under Mediterranean Climat. In comparison with the Precipitation S with Paris, it rains as much in Languedoc with the autumn, but in much less days. These storms give strong precipitations,

the coastal rivers and the the Rhone are thus enlarged rains received in the the Cevennes and from these storms of plain. They are in rising.

History

Each coastal river is known for its risings exceptionally devastators, often qualified wrongly centennial risings . Locally, the name of the river to which a Suffixe is assistant gives the name of these risings:

the Lez with Montpellier is known for its lézades .
the Vidourle, which passes between Nimes and Montpellier, violent believed named vidourlades with flows being able to reach 8 times that of the the Seine.

The Seine with Paris - Austerlitz, basin of 46.800 km ², (statistics banks HYDRO on 32 to 34 years, without integrating the years 1910 and 1955 thus) has, as average day laborers, an annual module of 310 m ³ /s (between 280 and 340), a biennial flow of 1.100 m ³ /s (between 980 and 1.200) and a decennial flow of 1.700 m ³ /s (1 500 to 1.900).
These same values for Vidourle with Marsillargues (798 km ²), (statistics banks HYDRO on 36 to 39 years) are respectively of 7,6 (6,1 to 9,4), 270 (230 to 330) and 560 (480 to 690) m ³ /s. In instantaneous flow, if that of the Seine east not very different from the daily output (to the more 10% of variation), the instantaneous flow of Vidourle is in biennial value of 440 m ³ /s (380 to 520) and for the decennial one of 850 m ³ /s (710 to 1.000).

the various rivers called Gardon (Gardon of Midsummer's Day and Gardon de Mialet which form together Gardon d' Anduze, Gardon d' Alès…), which meets to form Gard, very violent believed named gardonnades .

Topicality

With the autumn 2002, and by twice with the autumn 2003, took place of the episodes of Cevennes storm.

In 2002, the area of Ales and its close relations neighborhood were touched hard by these rains. Values of exceptional precipitations were recorded: such as for example 687 mm with Anduze and that in hardly twenty-four hours… (whereas it falls on average 650 mm per annum to Paris). 23 people are killed during this episode.
the Cevennes storm of December 2003 had devastators effects without precedent of the Aude until the Rhone delta:

the the Rhone flowed on several communes and plains of the Gard and Arles. 16 million m ³ crossed the town of Arles with a flow record of the the Rhone of 12 777 m ³ /s (1 800 in ordinary time).
the river Vidourle between the departments of the Gard and Herault flooded for the second time in two years the town of Sommières.
the Lez, the Mosson and various coastal brooks around Montpellier isolated the towns of Mauguio and the canton of Lattes. With 6 meters above its usual course, Lez reached in Montpellier and Lattes the height of its dams protecting the districts from these cities concentrating several tens of thousands of inhabitants.
the rivers Herault, Orb and Aude more in the west flooded the low districts of some cities and villages. For these rivers, their rising was prolonged on the littoral by the swell and the wind on the Mediterranean which prevented the rivers from being evacuated towards the broad one.

the repetition of the damage by these Cevennes storms at the same places and places, causes the despair of the victims and poses interrogations on the town and country planning in particular near rivers known for their periodic impetuosity.

See too

Hydraulic urban

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