Risle

The Risle (or Rille), Risela with the Middle Ages, is a Fleuve with waters running of Normandy, length 159 kilometers.

Hydrography

It takes its source in the Orne, to Tool bag-the-Glassmaking, enters the Département of the Eure in Herponcey (in the past Saint Denis d' Erponssai), limit of the department of the Flowering ash, close to Rugles, runs south in north-ouet while moving a little to the east and is thrown in the Seine, in Rocque, below Quillebeuf. Its valley traverses the Pays of Ouche then, with the approach of its mouth, forms natural separation between the two plates of the Lieuvin and the Roumois.

Risle, like the Iton, disappears temporarily: it is lost in a Bétoire, to the Châtel-the-Moon, not far from the Mill-Vault, and, in its underground direction, which is of 5 kilometers 1/2, it passes under the forest of Beaumont, and reappears close to the old castle of Groslay, with the Roger fountain, which the tradition called the Mad Fountain.

By the work made at the end of the XVIIe century, this river had been made navigable, since its mouth to Pont-Audemer; it reassembled there buildings of more than one hundred barrels, which came to exchange the foreign food products against the products of its territory and its industry, and made this city the center of a very wide trade; but the flood of 1711, caused by the extraordinary overflow of Risle, carried the head of the basin and fact in the channel of the excavations and the attérissemens (ground cluster, of sands brought by water) such as for this time one has not tried to repair the damage.

Last affluent of the the Seine, which it joined in its estuary, Risle, from an administrative point of view, is a nondomanial river except for the active sector of Pont-Audemer to the Estuaire of the Seine which belongs to the field Maritime.

Affluents

The Charentonne is its principal affluent. It also receives the Finard, the Sommaire, the Ruisseau of the Nozzle, the Véronne and the Sébec.

Crossed localities

Risle crosses, inter alia, the Eagle, Rugles, Beaumont-the-Roger, Brionne, Montfort-on-Risle and Pont-Audemer.

Hydrology

Like the close Iton, Risle is a remarkably regular river. Its annual medium flow, calculated over 41 years with Bridge-Authou (of 1967 with 2007), is of 12,1 m ³ a second for a surface of basin of 1.800 km ² (either 78% of totality).

The river presents a very regular mode, with weak seasonal fluctuations of flow. The high waters are winter and are assembled between 15,3 to 17,0 m ³ from January at March included. The thin ones of summer, from August at October, comfortable and are characterized by a weak fall of the monthly medium flow towards 8,4 to 9,1 m ³ a second.

The VCN3 can fall until 4,4 m ³, in the event of dry period quinquennial, which remains very comfortable. Let us recall that the VCN3 is the past minimal quantity or minimal flow over three days consecutive.

The risings are generally not very important but by no means non-existent. Thus the recorded maximum instantaneous flow was of 115 m ³ a second on March 26th, 2001, while the value maximum day laborer was of 87,2 m ³ a second the same day. The QIX 10 or calculated flow of decennial rising is of 68 m ³ a second, the QIX 20 of 78 m ³ and the QIX 50 of 92 m ³. The QIX 2 and QIX 5 are worth as for them respectively 42 and 58 m ³ (see note). From where it arises that the risings of March 2001 were exceptional, about the rising which occurs only once per century or centennial rising.

The Lame of water past in the basin is of 212 millimetres annually, a little lower than the average of the catchment area of the the Seine (220 to 240 millimetres). The specific Débit or Qsp is assembled consequently at 6,7 liters a second and per square kilometer of basin, which is extremely moderate and definitely less than the rivers of the Norman west.

References

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