From Ornans follow D67 towards Besançon.
After 1.2 km there is a parking lot on the right side, right before the bridge across the Brême.
5 minutes walk.
|Classification:||Estavelle Karst Spring|
|Guided tours:||self guided|
|Address:||Le Puits de la Brême.|
|As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then.
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The Puits de la Brême (Bremen Well) is a water-filled shaft with changing water levels. It is named after nearby river Brême, which is a tributary of the Loue. A branch of the river actually flows into the abyss, hence the name, although it is not the well or source of the Brême river. It is also called Trou Noir (Black Hole).
It's a daylight shaft of a water-filled cave, and the water level is the level of the groundwater. During low and medium wet weather, the water level is located a few meters below the top of the well. It has the typical blue colour of a Vauclusian spring, a result of the high amount of limestone filtering all colours except blue. The upper part of the shaft is oval and has a diameter of roughly 30 m by 20 m. If it is really dry the shaft is empty to the bottom, but there is still a narrow water-filled shaft leading deeper. As it is only 2 to 3 m wide and the sun does not reach that deep, it looks like a black hole, hence the name. But if there are heavy rains the groundwater rises and the well becomes emissive. Such wells which are wells at some point in time and sinks at another are called estavelle.
This spring is actually a part of a system of three connected wells, which are following the law of communicating vessels. The other two are the Source du Maine and the Source de l'Écoutôt. The two springs are resurgences of an underground cave river, the catchment area is the plateau north of the Loue river, between Ornans and Montrond-le-Château in the west and Valdahon and Passonfontaine in the east. The two springs have a certain diameter which restricts the amount of water, if there is more precipitation the groundwater rises and fills the estavelle until it overflows. If the precipitation shrinks below the production of the spring the water table lowers again. In other words, the Puits de la Brême is the overflow. The cave system which is responsible for this behaviour has not yet been explored. Until 2012 a 700 m long and 23 m deep siphon was crossed, an air filled passage named Salle Exondée discovered. The exploration ended in the second siphon at a depth of 48 m.