Holly-grove

The Houssière still called Oussière is a French Rivière which runs in the department of the Nievre (58), and more precisely in the solid mass of the Morvan. It is a direct affluent of the Yonne out of Right Bank, therefore a tributary of a tributary of the the Seine by Yonne.

Geography

The Holly-grove runs entirely within the Regional natural park of Morvan. It is born with the limit between the communes from Arleuf and Lavault-with-Frétoy. Its general orientation goes from is in west. It is thrown in the Yonne (Right Bank) with Chaumard, in an arm of the lake of reserve of Pannecière-Chaumard.

Common crossings

The Holly-grove has only one about fifteen kilometers length. It crosses only five communes, all located in the department of Nievre within the Regional natural park of Morvan:

Arleuf
Lavault-with-Frétoy
Corancy
Planchez
Chaumard

Hydrology

The Holly-grove is a very abundant river, like all the rivers of the Morvan. Its flow was observed over one 18 years period (1990-2007), with Chaumard, locality of the department of the Nievre located at the level of its confluence with the Yonne (ref.: ). The catchment area of the river is of 55 km ².

The interannual medium flow or module of the river with Chaumard is of 1,47 m ³ a second.

The Holly-grove presents seasonal fluctuations of flow marked well, like very often in the oriental party of the Massif Central, and Morvan in this case. She presents high waters of winter carrying the average monthly flow to a level located between 2,19 and 2,86 m ³ a second, from December to March included (with an in January maximum), and low waters of summer, July to September, with a fall of the monthly medium flow going up to 0,327 m ³ in August. But the fluctuations are much more marked over short periods and also according to the years.

With the low water level, the VCN3 can fall until 0,076 m ³, in the event of period quinquennial dry, which is rather low, but perfectly normal in these areas (see note).

As for the risings, they can be rather important, taking into account the extreme smallness of the catchment area of the river. The QIX 2 and QIX 5 are worth respectively 12 and 17 m ³. The QIX 10 or calculated flow of decennial rising is of 20 m ³ a second, the QIX 20 of 23 m ³. As for the QIX 50, it was not calculated fault one duration of sufficient observation (see note).

The recorded maximum instantaneous flow with Chaumard was of 33,3 m ³ a second on February 20th, 1999, while the value maximum day laborer was of 26,6 m ³ a second the same day. By comparing the first of these values on a QIX scale exposed higher, it arises that these risings were more abundant than cinquantennales, perhaps centennial, even more, but in all the cases completely exceptional.

The Lame of water past in the basin of the Holly-grove is of 845 millimetres annually, which is very high, even for the area. It is of course largely higher than the whole of the catchment area of the Seine (240 millimetres) and the Yonne (274 millimetres). The specific Débit (or Qsp) is assembled at 28,7 liters a second and per square kilometer of basin.

Curiosities - Tourism

the Lake Pannecière - Chaumard

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