Leysse

The Leysse is the Rivière which passes by the town of Chambéry, in the Département of Savoy. On its arrival in Chambéry, it disappears under the city thanks to a clever system from tunnel on the level from the Place from the Release to arise towards the Quai of Allobroges and to carry on its way until the Le Bourget-of-Lake.

Geography

It arrives of the Bauges (at the east) and is thrown in the Lac of Le Bourget more in north. Its water puts 7 to 10 years to reach the the Rhone.

It collects finally water of the Albanne at the southern entry of the city and those of the Hyères at the northern entry.

Hydrology

Leysse taking its source in the mountains, it can reach a very high level of water in winter (and sometimes in spring) at the time of the snow melt. This level reached besides critical points of flood to beginning of the year 90, imposing the installation of one of Prevention of the Risks of Flood (PR) whose mission is, with the Intercommunity association of the Rivers of the Basin Chambérien (SICEC) to prevent these risks of raw by proposing installations (ex: with the Leysse-Albanne confluence between 2004 and 2006).

But a contrario , the river drains only very little water during the summer (see photo opposite).

Flows

The interannual medium flow or module of Leysse was observed and calculated during 26 years with the Mound-Servolex with the bridge of Tremblay. It is assembled to 6,55 m ³ a second for a surface of basin of 280 km ². The river present of the typical seasonal fluctuations of flow of a rain mode at light nival component, with high waters of autumn-winter, prolonged in spring by the snow melt and carrying the average monthly flow on the level from 7,7 to 9,7 m ³ from November to April included (with an in March maximum - April), followed by a very progressive fall of the flow leading to one short period of low water level in August - September, involving a fall of the monthly medium flow up to 2,08 m ³ in August.

The VCN3 can fall until 0,108 m ³, in the event of dry decennial period. The VCN3 is the past minimal quantity or minimal flow over three days consecutive.

As for the risings, they can be important as described above. Indeed, the QIX 2 or calculated flow of rising biennial, and the QIX 5 or flow calculated for a quinquennial rising is worth respectively 112 and 157 m ³ a second. The QIX 10 or calculated flow of decennial rising is of 186 m ³ a second, the QIX 20 and the QIX 50 were not calculated. (see note). What means that every ten years, rising of 180 m ³ a second must statistically occur.

The maximum instantaneous flow recorded with the Mound-Servolex is of 221 m ³ a second. As for the most important daily output observed, it was of 160 m ³ a second.

The Lame of water past on this part (most important) of the catchment area of the river is of 742 millimetres annually, which is raised and results from abundant precipitations in the sector, but is completely normal in Savoy. The specific flow (Qsp) is assembled thus at 23,4 liters a second and per square kilometer of basin.

Photograph gallery

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