Liana (river)

Morphology

Its average slope is of 2,8 ‰. Its estuary was very artificialisé.

Affluents

Among those, one finds;

out of Right Bank: the brook of Lamy, the brook of Corette and the brook of Echinghem,

out of left bank, the brook of Lottinghem, the brook of Old Moutier, the brook of Menneville, the brook of Edre, the brook of Desvres.

Hydrology

The Liana is an extremely abundant, but rather irregular river. Its flow was observed during one 27 years period (1965-1991), with Hesdigneul-the-Boulogne, locality located close to Boulogne-sur-Mer, with little distance from its mouth (ref.: ). The catchment area of the river is there of 196 km ² (either 80% of its totality which makes 244 km ²).

Interannual medium flow or module of the river in Hesdigneul-the-Boulogne east of 2,99 m ³ a second.

Just as its neighbor the Wimereux, the Liana presents seasonal fluctuations of flow very marked, it contrary to the majority of the rivers of the Pas-de-Calais. The high waters are held at the end of the autumn and in winter and are characterized by average monthly flows located between 3,06 and 5,33 m ³ a second, from November to March included (with an in January maximum). The low waters take place in summer, from June to September, with a fall of the monthly medium flow going up to 0,76 m ³ in August. But the fluctuations of flow are much more marked over moreover short periods or according to the years.

With the low water level, the VCN3 can fall until 0,066 m ³, in the event of dry period quinquennial, that is to say 66 liters a second, which can be described as severe (see note).

As for the risings, they can be very important taking into account the modest size of this small river and its catchment area. The QIX 2 and QIX 5 are worth respectively 37 and 52 m ³ a second. The QIX 10 or calculated flow of decennial rising is of 61 m ³ a second, the QIX 20 of 70 m ³, while the QIX 50 is assembled to 82 m ³ a second (see note).

The maximum instantaneous flow recorded in Hesdigneul-the-Boulogne during this 27 years period, was of 47,3 m ³ a second on December 1st, 1979, while the value maximum day laborer was of 41,6 m ³ a second on February 6th, 1988. By comparing the first of these values on a QIX scale of the river, it appears clearly that this rising was hardly of a quinquennial nature, and thus intended to very frequently reproduce.

The Liana is a small extremely abundant river, well supplied with strong precipitations of its basin. The Lame of water past in its catchment area is of 483 millimetres annually, which is largely higher than the overall average of France all confused basins, like to the average of the basin of the Lys near for example (249 millimetres in Wervicq-South). The specific Flow of the river (or Qsp) reached the robust figure of 15,3 liters a second and per square kilometer of basin.

Ecological state

Except close to the source, the quality of its water poor with was clearly polluted in the years 1980-1990, because of wastes industrial and urban notamnent. The cities and industries pollute less, but the ploughing having gained ground with the detriment of the scrap-metal and pastures which moved back in this area, agricultural erosion and the grounds maintained naked in winter and autumn are a cause of almost constant turbidity of the Liana. In 2005, it remains turbide and of unsatisfactory quality (too many nitrates and of organic matters as of Carly, according to the Agency of water), but the situation should be improved by the application of the Parent directive European on water, and of WISE (diagram of installation and management of water) local.

Random links: