Drouette

The Drouette is small a French Rivière running in the departments of the Yvelines and the Eure-et-Loir, long 40 kilometers, Affluent of Right Bank of the the Eure. The name of “Drouette”, originally “Droue”, derives from a hydronymic root Dur-, gilded , which means “river”.

Geography

Drouette takes its source with the gold pond in the commune of Rambouillet (Yvelines), to 160 m of altitude, and runs in direction of the south by sprinkling the communes of Orcemont and Orphin, before forking towards the west, crossing the communes of Émancé, then entering in Eure-et-Loir, Droue-on-Drouette, Épernon, Hanches, Saint-Martin-with-Nigelles and Villiers-le-Morhier where it is thrown in the Eure, to 90 m of altitude approximately. In Épernon, it receives on its Right Bank, the Guéville and Guesle, two rivers also being born in the commune of Rambouillet and long each of 17 kilometers.

In 1932, the commune of Droue d' Eure-et-Loir took the name of Droue-on-Drouette being distinguished from its homonym of the Loir-et-Cher. More recently, in 2001, Drouette gave its name to the Communauté of communes of the Valley Drouette which joins together the communes of Droue-on-Drouette, Épernon, Gas, Hanches and Saint-Martin-of-Nigelles.

The management and the maintenance of Drouette and its affluents are ensured by an intercommunity association, the “Mixed trade-union of the three rivers” which joins together the trade union of Drouette (5 adherent communes in Eure-et-Loir), the trade union of Gazeran (11 communes) and SIVOM of Rambouillet (4 communes).

Hydrology

Drouette is a river very little abundant. Its flow was observed during 21 years (between 1987-2007), with Saint-Martin-with-Nigelles, very close to its confluence with the Eure. The catchment area of the river is there of 231 km ², which represents more than 95% of its totality.

The interannual medium flow or module of the river with Saint-Martin-of-Nigelles is of 0,888 m ³ a second.

Drouette presents seasonal fluctuations of flow not very important, following the example other affluents of the Eure. The high waters are held in winter and are characterized by average monthly flows going from 1,13 to 1,34 m ³ a second, from December to March included (with an in January maximum). The low waters take place in summer, from July to September included, with a fall of the monthly medium flow going up to 0,531 m ³ in August, which remains very comfortable for such a small river. However the fluctuations can be more marked over moreover short periods, and the levels fluctuate according to the years.

The VCN3 can fall until 0,26 m ³, that is to say 260 liters a second, in the event of dry period quinquennial, which is still not severe (see note).

The risings of this small river with reduced basin are not very important but by no means non-existent. The QIX 2 or calculated flow of biennial rising and QIX 5 (calculated flow of quinquennial rising) are worth respectively 6,6 and 9,7 m ³ a second. The QIX 10 or calculated flow of decennial rising is of 12 m ³ a second and the QIX 20 of 14 m ³. As for the QIX 50 or computed value of the flow of raw cinquantennale, it was not calculated, for lack of duration of sufficient observation (see note). That means that, for example, every two years, one must expect a rising of about 6 to 7 cubic meters, and every twenty years a rising of 14 cubic meters must statistically occur.

The recorded maximum instantaneous flow was of 14,2 m ³ a second on December 3rd, 2000, while the maximum daily output was of 12,0 m ³ on December 29th, 1999. By comparing the value of the maximum instantaneous flow on a QIX scale of the river, it appears that this rising was of a vicennial nature, and thus relatively frequent and intended to reproduce regularly, more or less every 20 years.

On the whole, Drouette is a river poorly abundant. The Lame of water past in its catchment area is of 121 millimetres annually (against 138 for the Eure), which is frankly weak, being worth definitely less than half of the average overall of France all confused basins, but especially lower than the blade of the totality of the basin of the Seine (240 millimetres). The specific Débit of the river (or Qsp) reaches only the very poor figure of 3,6 liters a second and per square kilometer of basin.

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