The Bèze () is a French river in the Côte-d'Or department, in the Bourgogne-Franche-Comté region. It is a right tributary of the Saône, and thus a sub-tributary of the Rhône.
The river rises in the Crétanne cave in the village of Bèze, then crosses several communes in its course before entering the Saône in Vonges. Its source is the outlet of a vast underground network fed by the Tille and the Venelle. A walk has been laid out around the spring, which is a major tourist attraction in the region.
The watershed of the Bèze river and its main tributary, the Albane, irrigates the Saône Vingeanne country, over a total area of Along its course the landscape alternates between forested areas and areas of large crops, livestock meadows and ponds. The basin is home to four natural areas of interest for their ecology, fauna and flora.
Human occupation along the river began as early as the Paleolithic. In Roman Gaul the sanctuary of Mirebeau-sur-Bèze, on an important axis of communication, was an important place in the region. The site was occupied by the Legio VIII Augusta, who built an imposing military camp. In the Middle Ages the river saw the foundation of the Abbaye Saint-Pierre de Bèze, a gathering place for the pilgrimage of Saint Prudent de Narbonne. In the modern era the Poudrerie nationale de Vonges was founded at the mouth of the Bèze, which it used for industrial purposes. It remains an important heritage building on the water.
The fauna and flora are similar to those associated with the Saône ecosystem, with a predominance of trout. Many hydraulic structures, however, have a strong impact on the river species. The water quality of the Bèze and its tributaries is considered mediocre due to nitrates from agricultural and livestock activities along the river's course. The Bèze and its watershed do not present any major natural hazards.
Geography and description
The source of the Bèze is north-east of Dijon in the Bèze village at an altitude of . It rises from a basin at the foot of the Kimmeridgian limestones and immediately forms a river wide. Other sources, connected with the underground river discovered in 1950 by the Dijon Speleo-Club, originate under the old cemetery of Bèze downstream. The river then travels in a southeasterly direction to discharge into the Saône, of which it is a tributary on the right bank, in the commune of Vonges, at an altitude of of altitude, where it is wide. Its average slope is 0.9%.
La Bèze flows through the center of the "Bèze-Albane" catchment basin in the heart of the Saône Vingeanne country, in the department of Côte-d'Or, with a total area of . The river is characterized by its source in Bèze, a remarkable spring fueled by a large underground network. Its watershed contains three tributaries and is bounded on the south by its confluence with the Saône.
Sources Location
The source of the Bèze is one of the most important karst springs in metropolitan France. The river originates in an underground lake in a cave called La Crétanne in the immediate vicinity of the agglomeration of Bèze, in Côte-d'Or, at the foot of a cliff overlooking the spring, in the basin called "la douy". The lake is discharged into the open through a tunnel similar to the Fontaine de Vaucluse. The tunnel, called the Salle Blanc (White Room), is with a ceiling, and can be entered by a small staircase at the foot of the cliff. The well-known La Crétanne cave is underground. It is about long, with four upstream tunnels and one downstream tunnel, the source of the Bèze.
Underground network
The underground network of the Bèze extends over , with a vertical drop of . The source of the Bèze, the outlet of this hydraulic network, is the most important karst spring of the Côte-d'Or department. The Crétanne cave is the best explored part of this vast network.
The underground network of Bèze consists of four sumps, or underground water channels: The source of the Bèze sump was prospected by the S.C. Dijon (Speleo Club de Dijon) and the S.C. Paris for the first time on 25 October 1953 along and a depth of . In 1972 the SHAG explored about more and then the S.C. Dijon, in 1974, reached the junction with the cave by crossing this sump of , which proved to be prolonged by side annexes, including a very dangerous downstream duct, for a total of . The pier sump (or sump 1) was unclogged in 1964, 1966 and 1967. The entrance was cleared during the year 1968. The embedded conduit between two strata runs for . It ends in a flooded well constituting the junction of several galleries. The main one was explored in 1975 up to from the entrance and to a depth of . The junction with the Lac Blanc sump was reached in 1976. In 1976 a secondary downstream gallery, beginning from the entrance, extended for and then emerged into a dry area. The Lac Blanc sump (or sump 2) was discovered in 1953 by the S.C. Dijon and the S.C. Paris and then explored for in a slightly immersed gallery to a submerged shaft at a depth of . Ancillary sumps, close to the entrance, were explored to about . In 1976 the main water supply was located from the entrance, the "Puits de la Chaussette". The junction with the pier sump was formed by a fracture long and high. A bell-shaped cavity was then discovered from the entrance. Three extensions were explored in 1978 and 1979: a very narrow crack surfaced in a small duct terminated by a flooded crack, a vast flooded chimney and a small upper network. The sumps of the scree gallery (or sumps 3 and 4) have no apparent current and contain many clay deposits. The first measures and the second .
Geology
The Crétanne cave is made of limestone. The set of galleries that constitutes the underground Bèze river have developed in layers of limestones that are not very thick ( on average) and were formed in the upper part of the Oxfordian or Astartian areas. This formation overlays a thick mass of limestone of quite variable nature from the Rauracian and Sequanian ages, with thickness of over , which constitutes the basement of the limestone plateaus to the north of Bèze.
The source is covered by limestone and marl of the Kimmeridgian age, which form a small cuesta visible to the southeast of the village of Bèze, under the compact limestone of the Portland Group. The ceiling of the cave is covered with kaolinite while the walls are covered with manganese oxide in some places. The set of galleries has a slight but steady incline towards the south, where it is covered by patches of Cretaceous rocks and then by the Tertiary sediments of La Bresse. The karst in the region must have been established either at the end of the Oligocene, or during the Miocene.
The galleries of the Bèze cave are parallel to the stratification of the layers. They are wide, with flat roofs that corresponds to the base surface of the limestone beds. It seems that are several levels of galleries. The highest are visible at the base of the first room and are all clogged. The main galleries contain a number of vertical chimneys that could have been formed as a result of upward erosion by water under pressure. The galleries are oriented in two directions. The principal gallery is oriented a few degrees east of north, parallel to the direction of the tectonic faults and the main joints of the region). The second is essentially perpendicular to the previous one and also corresponds to a joint direction.
The sediments of the Bèze cave were the subject of detailed study in the proceedings of the 1st International Congress of Speleology. The filling mud consists of siliceous sands identical to the albian sands found further south of the Bèze. The sands indicate the existence of the basin of an underground river of an old albian cover that has now disappeared. In addition, the greatest part of the filler consists of fine sand and silt that is increasingly fine towards the top of the series. Several cycles of sedimentation separated by calcite floors can be observed. Finally, varves are present in the upper galleries, formed during flooding, which are separated by darker layers and particles of finer size, deposited during periods of low water.
Hydrology at source
The source of the Bèze consists of two openings: The first, at the southern end of the underground river, where the water comes almost vertically through a sump obstructed by large collapsed blocks The second, the main opening, is about further north at the end of the Salle Blanc. The flow is greater than in the other outlet due to the presence of a sump. The Speleo Clubs of Dijon and Paris undertook penetration tests which showed the existence upstream of flooded galleries and then an almost vertical well of in depth leading to more flooded galleries.
A sump to drain the waters of the underground river is a short distance from the first water outlet, about from the Bèze karst spring, but is insufficient to drain all the waters during flood periods.
The average annual flow of the river at Bèze is . There are significant variations, with the low flow rate around and the maximum at times of flood reaching . The flow of the Bèze at its source was observed during a period of 27 years from 1981 to 2012 at the station in Bèze called the "Ferme de Rome" .
Origin of the waters The river originates in an upwelling of the waters of the aquifer under the forest of Velours in the commune of Lux, Côte-d'Or. This is fed by water from the Tille and Venelle rivers. The Speleo-Club of Dijon has explored the source since 14 July 1950. Exploration continues today by scuba diving and by systematic study of the discovered network. H. Tintant says that most of the waters of the Bèze come from underground drainage of the immense karst plateau consisting of rauracian and sequanian limestones forming a quadrilateral limited to the north by the impenetrable Argovian marls from Crécey-sur-Tille to Occey and the valley of the Vingeanne. Covered by dry valleys and perforated with numerous funnels (several hundred in the Velours forest alone), this plateau, which measures more than , is covered with very permeable rocks with a small but discernible slope to the south. The underground river feeding the Bèze at its source probably collects 50% of the annual rainfall on the plateau.
Fluorescein tests carried out by the Speleo-Club of Dijon in 1970 showed that the waters of Venelle colored those of the Bèze in the caves of the spring.
Fauna and flora
The Bèze cave is home to an endemic species, the Burgundy Asellus aquaticus, a freshwater species studied in 1969 by J.-P. Henry and G. Magniez. The underground river is home to crustaceans such as niphargus. Fish such as minnow, sculpin and trout can sometimes be found in one of the sumps. There are five species of bats. The flora is composed of ferns that have colonized the geological chimneys. Various types of moss and some fungi can also be observed.
The spring
The Bèze spring is at the point where the Sequanian limestone plateau dips under the more clayey or Kimmeridgian cuesta, which is similar to many Châtillonnais springs at the foot of the Aargau cuesta.
The geographer François Robert wrote in 1789 that the Bèze spring is one of the four most significant in France. The spring is the most photographed place in Bèze. Some postcard publishers do not hesitate to improve the picture by scratching the glass plate negative for a more impressive outpouring. The walk at the source around the spring is a monument historique site with construction dated to the 18th century and trees that are 200 to 300 years old.
Development
In 1970 the municipality of Bèze and its mayor, Robert Poinsot, decided to develop the cave, which is the property of the commune, for tourism. It opened to visitors in April 1971.
The caves can be visited by boat over a distance of about on the underground lake at a temperature of .