Thouet

The Thouet is a river of the west of France, one of the last affluents of left bank of the Loire, long 142 km.

Etymology

The name Thouet originates in a hydronyme Gallic on which the specialists did not find an agreement. According to some of the latter, it is about the quiet word tava meaning, followed suffix - Aris where the hydronymic root Ar finds, for others of toaro whose direction remains obscure. This toponym is also found in the names of Thouars and the Thouaret, one of the affluents of the river. Before the word of Thouet was not fixed at the 17th century, the river was called Fluvius Toarum at the 9th century, Fluvius Touverii around the An millet, then Thoer in various texts of the 14th century or Thoué towards 1567.

Geography

Thouet is born in Gâtine Vendean, last southernmost misadventure, with the Vendean Scrap-metal, of the Armorican Massif, with 225 meters of altitude. Its source, localized in the west of the department of the Two-Sevres, close to the farm of the Wire-nail works on the territory of the commune of Beugnon, close to Secondigny, is close to that of the Nantes Sèvre. The river traverses then two very different geological entities which explain the multiple aspects that its course presents:

in the south and the west, the Armorican Massive with the grounds granitic of the primary era, consisted of eruptive rocks and metamorphic. These not very permeable grounds cannot give rise to a Aquifère of importance but constitute zones of Ruissellement precipitations.
in north and the east, the Paris basin with the sedimentary cover of formed marine origin of Jurassic layers Calcareous S of the Aalénien higher than the Callovien. The nature of the rocks allows here the formation of a Aquifère whose reserves out of water ensures a support for the flows of low water level.

Of Saint-Wolf-Lamairé to Thouars, penetrating in grounds Calcareous S of the Jurassic lower and average, Thouet runs in an open and deep valley of about fifty meters. It alternates rectilinear sections and sections with Méandre S; a few kilometers upstream of Thouars, one of them, full and deep, form the circus of Setting offering an abrupt and wooded decoration rather unusual in France of the west. Of Thouars to Saint-Hilaire-Saint-Florent, place of his junction with the Loire, Thouet runs from now on on movable deposits of the Cénomanien embanked by Alluvions Quaternaire S. Its valley, corresponds to a broad depression from 1 to 2 km, is marked little, being boxed only twice: with Montreuil-Bellay and in its ultimate race between Varrains and its union with the river ligérien (it meets genuine formed chalk cliffs and crayo-argillaceous limestones or Tuffeau). The river describes some sinuosities but which do not have the width of the meanders met upstream.

Hydrography

The Bassin pouring of Thouet extends on an total surface area from: 3396 km ², being distributed in an unequal way on 3 departments, the north of the Two-Sevres, the North-West of the Vienna and the part south-eastern of the Maine-et-Loire. It presents an irregular form whose average altitude gradually decrease south-west towards the North-East, from the source towards the mouth of the river which presents an average slope of 2,5 ‰. This last has the effect of being much denser on left bank where many affluents occurred in the Vendean Gâtine than on Right Bank where the only notable tributaries (particularly the Dive) come to feed the river in the last part of its course.

Contrary to many rivers French which obtained organizations of management of their catchment area and of a Schéma of installation and management of water (WISE), Thouet and its affluents do not have single institution, their water are managed by several trade unions whose collaboration leaves something to be desired preventing any joint action. It is thus difficult to provide precise data on the safe basin in purely geographical terms. Limited by 4 cities forming a quadrilateral (Saumur in north, Parthenay in the south, Bressuire in the west, Loudun in the east), this area catchment account approximately: 200000 inhabitants near his source or with Saumur close to its junction, the annual average temperature is about 12°C (with a minimum of January about 5° C and a maximum of July of 20° C). The relatively regular Precipitations, on the other hand, do not present the same homogeneity knowing a decrease according to a south-western/north-eastern gradient. The course upstream of Thouet and its affluents of left bank, near to Gâtine Vendean, knows abundant annual precipitations of about 900 mm (with a maximum of: 1058 mm with Saint-Aubin-the-Cloud). On the other hand, the downstream part and the area drained by the Divine in the east, are definitely sprinkled, precipitations dropping to 700 mm, even less with Saint-Martin-with-Mâcon (506 mm) The flow measured at the hydrological station of the bridge of Chacé, little upstream of Saumur, with a few kilometers of the junction with the the Loire, is on average of 19 m ³ /s within the framework of a rain Régime oceanic. This flow presents very strong annual variations with one period of high waters concentrated in winter (respectively 41,7 m ³ /s in January, 49,7 m ³ /s in February and 32,2 m ³ /s in March) and of particularly marked low waters during the summer period: 3,99 m ³ /s in July, 2,98 m ³ /s in August, 3,07 m ³ /s in September. The coefficient of excessivity (relationship between the monthly flow lowest and highest) is very strong, about 16,68.Il is explained by the nature of the rocks which supports a brutal and immediate flow precipitations combined with the stronger evapotranspiration in summer than during the winter. This type of mode can lead to a fast rise of water in the event of abundant precipitations and thus to the risk of Crue S during 7 months of the year (of at the end of October in May) or in December 1999. In 1911, a rising of Thouet had however dramatic consequences. November 23rd, tumultuous water of the river carried the single pile of the metallic bridge of the railway Angers - Poitiers with one kilometer of the station of Montreuil-Bellay whereas a convoy engaged on the work. The machine and three cars of travellers were precipitated in the floods and, in spite of the diligence of the rescuers, this railway catastrophe made 16 victims

Navigation on Thouet

Who discovers this peaceful river with the crossing of a bridge would have sorrow to imagine that it was formerly covered with heavy boats charged to the descent mainly with Vins, of brandies, cereals, Tuffeau X, and the increase of coals, Ardoise S, Plâtre S and other goods.

As on many rivers, it is impossible to determine the time as from which trading vessels started to circulate on Thouet. The first mention of a navigation (or rather of the possibility of borrowing the course of the river) goes up at the year 1430 when merchants brought together in assembly with Saumur submitted the project to make the river navigable in its angevine part, i.e. between its junction with the the Loire and Montreuil-Bellay. The navigability of Thouet claimed the creation of three marine doors in the roadways of the mill S existing downstream from the bridges of Montreuil-Bellay to allow the passage of the boats. It is possible that boats transported already goods on the river before this date, the cargo being transferred, using cranes, on boats different with the passage from each obstacle. At the 15th century and 16th century, a system of lock S with only one carries marine (or perhaps two at the end it 16th century, to see above) made it possible the boats to cross the roadways of the mills, but it was not without danger because they were likely to capsize, pulled by the powerful one running caused at the time of the opening; moreover, if the door were simple, this opening caused an important water loss leading to the stop of the activity of the mills for one more or less long period. In 1608, the presence of three basins to marine doors (basins closed by two of these last) is attested, one in the Room, in the past Saint-Hilaire-the-Senior, the two others in Rimodan and Bron, commune of the Coudray-Macouard; this last being today the only accessible one to the public. However in 1608, the specialists cannot determine if it were a question of creating new basins with marine doors (whereas the technique of the lock " moderne" was almost at the point) or to repair those existing already.

To facilitate the operations of loading and unloading of the ships, a Port was established in Montreuil-Bellay on left bank of Thouet at the beginning of the 17th century which took the name of Port Guibert . It was moved on Right Bank in 1710 because of the construction of a new bridge on the river and was located with the foot of the Rempart S of the city. During this two centuries period, various installations had to undergo the whims of Thouet (floods, raw) which obliged the lords of Montreuil-Bellay to carry out important repairs by increasing tolls as in 1662 - 1663 and in 1771. A project to make navigable the river until Thouars was proposed in 1746 but remained dead letter. At the time of the drain of Divine in 1834, were built on this one and Thouet, downstream from the junction, of the modern locks with rectilinear chamber walls and busquées doors, in Saumoussay and Saint-Hilaire-Saint-Florent in particular to replace old the sluice. Administratively, these locks belong to the Canal of Divine the, whereas for the geographer, the Divine one is an affluent of Thouet. A third lock " moderne" was built at the same time on Thouet, but upstream of the confluence of Divine, on a derivation with Lamotte, to replace the sluice, moreover always visible.

But it was too late because the river trade was soon condemned vis-a-vis the competition of the roads become more suitable for motor vehicles, and the railroad, was appeared in the area in 1874. The gauge known as " Becquey " inland waterway proved to be insufficient (locks of 32 m out of 5,20 m, with a damping of 1,60 m)

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