Rivière souterraine de Beaudemont (puits d'accès)

Two routes lead to the river: a natural gallery where one must crawl on all fours and, parallel to it, separated from it by a wall first artificial, then natural, a gently sloping built corridor.

A larger gallery, only 7 metres long, descends straight onto the river, which it overlooks by 3 metres.

If one enters the downstream part, narrow and winding, one comes up against piled stones blocking the passage. Upstream, the river is wider but the ceiling lowers steadily to 50 cm above the water. Beyond, it rises again and disappears under rockfalls. One is at the entrance to a collapse-strewn crossroads chamber guarded by a block fixed in the earth: the "menhir". The left gallery leads to a sump. To the right, an ascending passage leads to a recess of no interest.

One cannot follow the downstream course of the river because it is lost in the chalk. As a whole, the river is clayey, which seems to indicate, during high-water periods, the flooding of part of the cavity.

According to Mazoit: "The arrival of the water is obstructed by a collapsed pocket of sand which, creating a natural filter, means that, a rare thing, the water of this underground cavity is drinkable". Its resistivity is high (3 000 ohms/cm) and its nitrate content normal for this region (16 mg/l).

A concrete wall at the foot of which the pumping station is installed prevents direct access to the upstream course. By a 3-metre climb, one regains footing in the natural gallery, which one leaves through a skylight opening into a larger gallery.

Source: Spéléo-Club de Chablis > Rivière souterraine de Beaudemont (89464 - Villeneuve-sur-Yonne) -- https://www.scchablis.com/Site/Speleo/Invent/89/89464/beaudemont.php