Blaise (affluent of the Eure)

Geography

The Blaise takes his source with the Raspberry bed in the Forêt of Senonches in the department of Eure-et-Loir not far from the limit of the Orne, and joined the the Eure, of which it is a Affluent of left bank, close to Fermaincourt (commune of Cherisy).

Common crossings

Long approximately 45 km, it crosses many Village S: the Raspberry bed, Louvilliers-the-Pole, Maillebois, Saint-Angel-and-Torçay, Saulnières, Crécy-Brooded, Aunay-under-Crécy, Tréon, Garnay and finishes its course in the agglomeration drouaise crossing successively Vernouillet, Dreux and Cherisy.

Hydrology

The annual medium flow or module of the Blaise, observed during one 30 years period (of 1974 to 2003), with Garnay, locality located little before its confluence with the Eure at two kilometers downstream from Dreux, is of 1,96 m ³ a second for a surface of basin of 413 km ² (ref.: ).

The Blaise presents seasonal fluctuations of flow extremely moderate. The period of high waters proceeds in winter and at the beginning of spring and is characterized by average monthly flows going from 2,16 to 2,58 m ³ a second, from December to April included (with an in February maximum). As of April the flow decreases gradually to lead to the period of the low waters which takes place from July to September included, with a fall of the monthly medium flow going up to 1,46 m ³ in August, which is still frankly abundant, for a small river. However the fluctuations of flow can be more important according to the years and over shorter periods.

With the low water level the VCN3 can drop until 0,820 m ³, in the event of dry period quinquennial (see note), that is to say 820 liters a second, which is very far from being severe and remains even abundant.

The risings however can be relatively important. The QIX 2 and QIX 5 or calculated flows of biennial and quinquennial rising are worth respectively 14 and 20 m ³ a second. The QIX 10 or calculated flow of decennial rising is of 25 m ³ a second, the QIX 20 of 29 m ³, while the QIX 50 is assembled to 34 m ³ a second (see note).

The recorded maximum instantaneous flow with Garnay during this period, was of 27,2 m ³ a second on January 6th, 2001, while the recorded maximum daily output was of 22,6 m ³ a second on January 23rd, 1995. If one compares the first of these values on a QIX scale of the river, one notes that this rising was not even of a vicennial nature, i.e. by no means exceptional.

On the whole, the Blaise is a river poorly abundant, like the majority of his neighbors of the south-west of the basin of the the Seine and the basin of the the Eure more particularly. The Lame of water past in its catchment area is of 150 millimetres annually, which is definitely lower than the average of France, all confused basins, and also with the average of the basin of the Seine (more or less 240 millimetres). The specific Flow of the river (or Qsp) reached of this fact the figure relatively low of 4,8 liters a second and per square kilometer of basin.

References

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