Geography of Charente

The Département of Charente was cut out according to geographical criteria: the upstream reservoir and average of the homonymous river which crosses it. It belongs to the area Poitou-Charentes.

Situation

Charente is centered on its river, which occurs on the granitic plates of the the Limousin and leaves the department towards the west and the Charente-Maritime. This department is bordering on those of the Vienna, of the High-Vienna, the the Dordogne, the Charente-Maritime and the Two-Sevres.

The borders of the department of Charente coincide with the limits of the basins superior and means of the river Charente, which makes him include areas geographically and geologically very different which are of upstream downstream, Confolentais or Charente limousine, the Angoumois, then Saintonge.

The main cities of the department are built in loops of the river: Mansle, Angouleme and its perish-urban Saint-Yrieix-on-Charente, Hinge-Pontouvre, Fléac, the Crown, then downstream Châteauneuf-on-Charente, Jarnac, Cognac. Montbron and Rochefoucauld are on the Tardoire, Saint-Claud on the His, Aigre on the Aume. On 21 chief towns of cantons which account the department, 14 are on the river or its affluents.

Geology

If is department belongs to the Massif Central (plate of the Limousin), relic of the chain Hercynienne, the majority of Charente is in the Aquitanian Bassin, made up of sedimentary rocks of marine origin.

Confolentais or Charente limousine in the east of the department, is geologically located in the Limousin. Its ground presents a base of impermeable, and various rocks crystalline granitoid of the Limousin, especially of granitoid carboniferous and Granite with very fine grain, the pseudoporphyritic granite in biotic of Confolens. Towards Exideuil, the presence of leucogranite of Jump shows that it is about one of the most recent solid masses of the Limousin.

This area was pilot of an major event 214 million years ago, the impact of a meteorite of more than one kilometer in diameter which fell to Pressignac, halfway between Chassenon and Rochechouart. From where the impactic structure of Rochechouart with presence of a brecciated formation of 280 km ² having an axis is western of 18,5 km and a thickness of less than 100 meters, with the existence of breaches, shocked quartz and cones of percussion.

See also: Astroblème de Rochechouart-Chassenon

A little more in the south one finds very important red clay pockets which were exploited since Antiquity, in particular around Roumazières-Loubert. There are of them others in the south of the department towards the sources of the Né and the Seugne and along Right Bank of Charente what explains the number of potteries, tileries, brickyards which existed and the frequency of toponymy " tuileries"

While going towards Angouleme, carbonated and karstifiées bases of the Western edge of the Massif Central are found under impermeable argillaceous marnes. The subterranean water of the karst of Rochefoucauld is the consequence of these geological formations.

The north parts and is Angoumois going to Right Bank of the Touvre and overflowing it on a part, dates from the Jurassic higher with provision of is in west of increasingly recent outcrops.

The southern and western part starting from the south of Angouleme dates from the higher Crétacé and forms a cut out plate of parallel valleys. These rock valleys, their cliffs and their shelters under rocks are rich layers because they were inhabited by the man since the Neolithic . While going towards Châteauneuf-on-Charente one finds zones of Calcaires white and hard which were very exploited during the centuries, of the marnes and of detrital limestone, of thin layers of clay and sand the zones of the lower Coniacien a thickness active to 7meters towards Torsac.

From Jarnac it is the river which marks the geological limit: in north, Right Bank, a Jurassic zone , and at the south, left bank, a zone Cretaceous E with cuestas (plate with double asymmetrical slope).

The Right Bank of Charente has a little accentuated relief which goes down gradually towards the river. This zone which dates from the Tithonien (in the past named stage Portlandien), to the limit of the grounds of the Jurassic higher and the lower Cretaceous (Berriasien stage) presents a fine limestone then downstream in the " the Netherlands " outcrops of marnes and clays with gypsum. These tender deposits are in a wet depression where from Châteauneuf-on-Charente in the Charente-Maritime the river and its affluents Right Bank released from broad alluvial valleys.

Geology was particularly studied on the level of the career of Gypse of Champblanc on the commune of Cherves-Richemont during the excavations of the paleontological Site of Champblanc. It is old a tropical Lagune where, during time, followed one another of the marine and continental influences. The climate was rather hot, brackish water, and the lagoon underwent a strong evaporation, from where the deposit of the layers of Gypse and, in the intermediate marnes, an exceptional quantity and a diversity of Fossile S. the career with open sky shows on thirty to forty meters height of alternations of benches of gypsum, marnes, limestones or black clays which one believed initially not very fossiliferous, except a layer dated from the Berriasien (141 to 135 My) lower than means, which corresponds to the whole beginning of the Cretaceous, where the very many remainders of Vertébré S accumulated: a bone-bed.

The left bank of Charente presents an abrupt cliff which forms the edge between grounds of Jurassic the superiors and grounds of the Cretaceous. This cliff shows Cénomanien surmounted Turonien. All this part in the south of the river is a zone Crétacé E with cuestas, of limestones of the cénamoniens average and lower, and the zone of the Santonien which goes until Segonzac is continued towards the south by the zone of Campanien.

In the extreme south of the department a zone of the tertiary sector forms a dune sand ground.

The richness and the diversity of the basement explain the seniority of the minings: red and white clay, gypsum, stone of size, sand but also now exhausted or at least abandoned layers: iron in particular around Angouleme, manganese close to Montbron, money and lead close to Allocates.

Hydrology

Except on the level of Confolens, because the Vienna depends on the agency of basin Loire-Bretagne, the Département of Charente is in the zone of management of the agency of Adour-Garonne basin, which it sagisse of the Charente or in the south of a small portion of the Dronne.

Surface waters

The mode of the rivers is of rain type with high waters the winter and low waters the summer. At the time of the risings the rise of water is progressive, it begins upstream and continues towards the downstream according to a well-known chronology. The flooded grounds are it in a way usual and prolonged, of the roads are crossed and the quays of Angouleme and Cognac closed with circulation.

The rivers have a permanent flow because even in period of low water level, they profit from contributions of dependant tablecloths present in the sedimentary grounds. But of the too important taking away compared to the resource brought severe assecs, 570 km cumulated in 1990 what brought the installation of a plan of management of the taking away with volumetric management for the irrigants and of installations or refittings of the works on the rivers.

Lakes

The High-Charente Lakes, were created by two stoppings, the stoppings of the Farmhouse Chaban and the dam Lavaud built in 1989 and 1990. The Lac of Lavaud is located on Charente. The Lake of the Farmhouse-Chaban located at 3,5 km in the west east on the Moulde, at 3 km upstream of the junction Charente/Moulde on the communes of Lésignac-Durand and Massignac. The purpose of they occupy 400 hectares and are to support the low water level of the river during the summer

Charente and affluents

other rivers

Vienna which runs towards the east since Saint-Junien, passes to Chabanais and with Exideuil and the time when it will join the Charente transfers full north, passes to Confolens and leaves Charente for the Vienna and later joined the the Loire.
the Dronne which comes from the Massif Central arrives to Charente a little front Aubeterre-on-Drone. It already received water of the Lizonne to the southern full course since Villebois-Lavalette. It receives water of the Tude, and after having more or less been used as departmental limit, Charente in its extreme south leaves then is thrown in the Isle, affluent of the the Dordogne. Its valley is classified Natura 2000.

Ponds and marsh

The ponds extremely many and are disseminated. The impermeability transforms all the old loam pits and other excavations after extraction, but also the sand pits of south-Charente in water levels and ponds of fishing. Some of these ponds are ZNIEFF where countings of birds are carried out (ponds of Orlut on Cherves-Richemont for example)

The zones of marsh were numerous in the west of the department (as the toponyms of them “fen attests”). They were the valleys of the Né and the Antenne and floodplains transformed into pond around the Fossé of Roy as well as vast zone in the sector of Gensac-la-Pallue (in Pallue, there are two marshes, of Rulle and Grand marsh and a river is born from a source in the marshes). Currently one studies feasibility to return to them to these marshes their role of zones of expansion of the Charente river and thus to decrease the impact of the floods in the built-up areas.

Deep water

Is Charente-Limousine is a base christallin bordered by an aquiferous zone calcaréo dolomitic of lower Jurrassique North-South rather narrow. Then, more to the west, extends a calcareous aquifer from average Jurrassique and to the west from the department two aquifers Marno-limestones from Jurrassique higher and more to the south of Santonien Campanien bordered than its North-East by of Turonien Coniacien and to the south of a detrital aquifer of the Tertiary sector.

Thus while going from the east towards south-west, one find tablecloths captive, semi-captive then free tablecloths, generally of the alluvial tablecloths in relation to a river of which one of most important is that of the Island Hammer which feeds Cognac and its periphery out of drinking water.

The remarkable geological formation is the ic plate Karst of Rochefoucauld extends on more than 500 km ². The underground advance of water created pits and named depressions pits (mobile pit, pit limousine, large pit). It has a very great storage capacity and it is fed in particular by water of the Bandiat and the Tardoire which disappear there in almost totality, and by the Bonnieure. This water forms underground rivers and contiguous resurgences, the Ebullient one, the Door frame and Do it of Lussac and Licks it, which constitute the Touvre, the more important second French Résurgence. The cause of resurgence is the Faille of the Scale where a 500 m thickness of marnes of the Kimméridgien lower impermeable bar the road than the underground flow of water and obliges them to go back to surface. The Scale is also thrown it in the source. The food of the town of Angouleme is done on the karst of Rochefoucauld on the level of the Ebullient one. This network includes/understands in addition to the active level that are the underground rivers, of the fossil networks and the networks half-credits, pits of collapse and cavities fossil like the cave of Quéroy.

Use of water

For the Department of Charente in 1995 per 103 million m3, only 30,7 were used for the distribution of Drinking water, 21,95 for industry and 50,5 for the irrigation. The actions undertaken bore their fruits since 1998 with a fall to 98,6 million m3, including 31,2 for the drinkable water supply, 17,4 for industry either a fall of 20% and 45 for the irrigation or a fall of 10% which was accentuated the following years.

For the whole of the basin of Charente (Charente and Charente-Maritime) the taking away were into 1996 of 208 million m3 including 67 for the drinkable water supply, 26 for industry and 116 for the irrigation. And, in period of low water level the distribution of the uses becomes of 90% for agriculture, 9% for drinking water and 1% for industry. Of this fact the estival chronic deficit tends to worsen.

The water used for these different uses comes from captive tablecloth and ground water but surface water also (10,4 for drinking water, 6,34 for industry and 15,97 for the irrigation) (3,77 for drinking water, 1 for industry and 6,48 for the irrigation) (figures 1995). Other figures show that in 1998 the drinking water in Charente came for 98% from subterranean water, taken for 54% in captive tablecloth, 20% in semi-captive tablecloth and 26% in free tablecloth.

One of the health questions public is the increase in water of the collectings intended for drinking water of the rates of Nitrate S and of Pesticide S. These increases can be a slow increase, or, for the free tablecloths of sudden rises following strong rains having caused streaming and a scrubbing of residues of plant health products agricultural. Many collectings have being closed (in Charente, more than 100 in 10 years) and the water cuts in the Southern periphery of Angouleme had a gravity which made become aware with the totality of the population of the gravity of the situation.

Occupation of the grounds

The grounds are extremely varied with the North-East in the south-east of the grounds of old solid masses, grounds of brandes, grounds of groies, grounds marly and dune sands, all these grounds being crossed broad alluvial valleys. This explains the diversity of the landscapes with mainly in the west on the calcareous plate the vines of the area of appellation contr4ol3ee Cognac, in the south the forest of pine, the east the forests of leafy trees and coniferous tree, in north a zone of plain with scrap-metal in the North-East. The whole is cut by the easily flooded alluvial valleys where the cities are built.

Natural spaces

The department of Charente entirely comprises 24 zones Natura 2000 some in the department, others partly on the departments bordering, especially the Charente-Maritime but also the the Dordogne and the High-Vienna. They are several types, on the one hand rivers and their valley, and particularly Charente on almost the totality of its course and the majority of its affluents, on the other hand some specific spaces, lawns calciformes, thatches and slopes as well as a forest and a cave. They relate to several great types of habitats: those of Bird X, those of Chiroptère S (the bat), those of Otter S and minks of Europe, and those of the orchises. Invertebrates, Amphibian S and remarkable Poisson S are also listed.

The plain of Villefagnan on its 9531 ha and the plain of Barbezières to Gourville on 8108 ha have a great diversity of remarkable birds, raptors, Bondrée apivore, ashy Busard, Busard of the reeds, Hen harrier, Faucon swivel, Faucon small landed proprietor, Epervier of Europe, waders which are also present at the edge of Charente white Cigogne, ashy Grue, ashy Héron, of limicolous the ashy Courlis, yelling Oedicnème, Pluvier gilded, crested Vanneau and also Nightjar, Small-duke scops, black Milan, royal Milan, Shrike flayer (Lanius collurio), Pipit rousseline (Anthus campestris). On Villefagnan are also present the woodcock of wood, the Bruant ortolan bunting and the Hibou of the marshes.

An important action of safeguarding of the Outarde canepetière was undertaken, from conventions were passed with the farmers to modify dates of mowings and to mow interior of the field towards outside for thus letting the birds escape.

On the valley of the Charente upstream of Angouleme 64 species of remarkable birds were counted. Among them species of marsh and wetlands are, those met in Villefagnan and Barbezières and also of other limicolous (elegant Avocette, Bécassine of the marshes, Barge with black tail, deaf Bécassine, white stilt, Grand Gravelot, Petit Gravelot, Redshank, Chevalier guignette, Chevalier Sylvain, and Combattant varied (species very rare), waders (black stork, large Brush, Aigrette garzette, gray Bihoreau, dwarf Blongios, purple Héron).

Among the plunger birds and swimmers, swans (Swan tuber), grèbes (Grèbe with black neck, castagneux Grèbe, Grèbe esclavon, crested Grèbe), geese (greylag goose), ducks (Duck chipeau, Duck pintail, Wigeon, Shoveler), teals (Teal of summer, Teal of winter), and fuligules (Fuligule pochard, Fuligule tufted duck).

The terns (tern pierregarin), the guifettes (Guifette moustac and Guifette black), the gulls (Black-headed gull), the Large Cormorant, go up per periods very upstream on the river.

There are also peaks (Torcol fourmilier), raptors (osprey, peregrine falcon), Martin-pêcheur, Gorgebleue with mirror, reeds of the snap rings, and corncrakes in addition to all the current species which they are not classified remarkable.

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