Bétoire de la Risle

Useful Information

Location:	1 Rte de Bernay, 27410 Mesnil-en-Ouche. A13 Paris-Rouen, exit 15 Évreaux, follow N13 to Évreaux, D830 to Conches-en-Ouche, the bypass D830 to turnoff Bernay/Le Vieux Conches, turn left D140 to La Ferrière-sur-Risle. The swallow holes are where the D140 crosses the Risle. (48.978756, 0.783229)
Open:	no restrictions. [2023]
Fee:	free. [2023]
Classification:	Losing Stream Ponor Karst Spring Subaquatic Spring
Light:	bring torch.
Dimension:
Guided tours:	self guided
Photography:	allowed
Accessibility:	no
Bibliography:	Jean François Gabriel Vaugeois (1841): Histoire des antiquités de la ville de Laigle et de ses environs, L'Aigle, P.-E. Brédif, 1841, p. 4-5 online Pierre-Yann David, Didier Pennequin, Baptiste Meire, Jean-Baptiste Charlier, Veronique Feeny-Fereol, Stephane Helouin, Matthieu Fournier (2018): Evolution des phénomènes karstiques dans la Risle Médiane, étude de la dynamique des pertes de débits, impacts sur les eaux souterraines Géologues, 2018, L’hydrogéologie de la craie, 199, pp.83- 88. hal-02571271 HAL researchgate
Address:	Bétoire de la Risle, 1 Rte de Bernay, 27410 Mesnil-en-Ouche. Pisciculture de Fontaine à Roger, Chem. de la Bigottière, 27170 Beaumont-le-Roger, Tel: +33-232-45-45-56.
As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then. Please check rates and details directly with the companies in question if you need more recent info.

History

28-JUL-2012	sinkhole opens in the river and swallows all the water.
15-JUL-2013 to 19-JUL-2013	sinkholes filled with rocks.

Description

The Bétoire de la Risle (Sink of the Risle River) is a swallow hole in the river, which swallows all water of the river during summer. The water flows underground and reappears after about 9 km in Fontaine à Roger near Grosley-sur-Risle and in various springs in the riverbed. The Risle is 145 km long and is a left tributary of the Seine, its spring is at an altitude of 275 m asl in the wood of Boulais. The upper part is on impermeable rocks, then it reaches an area of karstified chalk, which is called the Risle perchée. The limestone rocks are from the Upper Cretaceous (Senonian, Turonian, and Cenomanian), more or less the same soft and white rock as at the cliffs of Dover. In this area there are numerous karst springs feeding the river, but also numerous swallow holes where the river sometimes looses a part or all water to the aquifer. The area between the Risle and its tributary La Charentonne has more than half a dozen brooks which flow into ponors to reappear in the subfluvial springs of the Risle.

Les eaux de la Rille, dont le volume diminue déjà sensiblement au-dessus de Rugles, disparaissent entièrement au-delà du Moulin-Chapelle, au-dessous de la Ferrière. À cinq quarts de lieue au-delà, elles ressortent de terre, près d'un village nommé Grosley, où elles forment une source très forte que les habitants des campagnes voisines, qui ont oublié son véritable nom, appellent la fontaine enragée (on lit même dans une des copies du manuscrit de l'Aigle, la fontaine arragée). Son vrai nom était la Fontaine-à-Roger, parce qu'elle appartenait aux anciens comtes de Beaumont-le-Roger, dont la forteresse était près de là.
The waters of the Rille, whose volume already diminishes appreciably above Rugles, disappear entirely beyond the Moulin-Chapelle, below La Ferrière. Five quarters of a league further on, they emerge from the ground, near a village called Grosley, where they form a very strong spring which the inhabitants of the neighbouring countryside, who have forgotten its true name, call the enraged fountain (in one of the copies of the Aigle manuscript, it even says the raging fountain). Its real name was the Fontaine-à-Roger, because it belonged to the ancient counts of Beaumont-le-Roger, whose fortress was near there.
Jean François Gabriel Vaugeois (1841): Histoire des antiquités de la ville de Laigle et de ses environs, L'Aigle, P.-E. Brédif, 1841, p. 4-5 online

The Risle river and the nearby Iton river were known to fall dry during dry summers until the 19th century. Similar descriptions exist from various authors, like Auguste Le Prévost, or Pierre-Charles Piquet, geographer to the King. However, people used the water for various purposes, and so they tried to keep it on the surface by filling in the swallow holes. This was at the end of the 19th century, the exact date is unknown. From then on the river flowed all year, at least until 28-JUL-2012 when a new sinkhole opened in the river and swallowed all water. The river became dry for about 12 km (9 km as the crow flies) until the water reappeared in various springs.

As the river vanished completely, the plants and fish in the river died, and it was seen as an economic and ecologic desaster. The fish died and so it was mainly a problem for the fishers and some farmers along the river who used the river as drinking water for their cattle. Also, the stability of some bridges in the now dry section was threatened by the lack of water, for example the bridge over the Risle in Grosley-sur-Risle.

The new swallow hole in the river is located between La Ferrière-sur-Risle and Ajou. The city planned to build a canal around the swallow hole or to fill it in with rocks. But the bureaucracy is slow, and it took until October, when Dominique Sorain, the prefect, decided to issue an order authorizing the partial filling of the ponor. But it was too late, heavy rains had filled the aquifer and the sink did not swallow all the water anymore. And with a heavy current flowing down the river it was not possible to fill in the ponor. As a result they had to wait until the following summer and the next low water. In the following year on 15th and 19th July a total of 150 m³ of rocks were placed in the ponors of the section of the river between Ajou and La Houssaye. As a result the river has not disappeared completely anymore.

It seems, the locals should have been aware of the situation. There is a long history of vanishing rivers during summer in the area. And even after the ponors were filled, in the late 19th century, there must have been some loss during summer, just not as much as before. And it's the same now, there is still a lot of water vanishing, just less than before and the river does not become dry anymore. And why actually the massive outcry? The loudest complaints came from the Fédération de la Pêche et de la Pisciculture de l’Eure (Eure Fishing and Fish Farming Federation) for obvious reasons. There were people on the brink of despair and there was a lot of scaremongering in the newspapers, even apocalyptic warnings that the river will be gone forever. Obvious nonsense, and also semantically wrong: the river has not disappeared, it merely flows underground. Objectively, the fishermen lose a few kilos of fish, the farmers have to carry water to their cows in tankers, and it smells a bit harsh because the plants and fish are rotting. And yet, the whole situation is natural, the karst area is on the threshold of maturing to underground drainage. The natural development would be that the river regularly goes dry every summer, a little later water only flows sometimes after heavy rains, when the river is reactivated, and at some point the water disappears when it reaches the chalk and reappears in springs on the other side. This development might take a few thousand years. The ecologic disaster is the filling of the ponors, like people pulling dead trees out of a natural forest. Other dry, rocky riverbeds elsewhere became extraordinary habitats because of their unique properties, they are generally protected as Natural Monuments

It seems the government was aware that the filling in was actually nonsense, so they created a Risle observatory to prove the opposite. It is piloted by the BRGM (Bureau of Geological and Mining Research), the Dreal (Regional Department for the Environment, Planning and Housing), the University of Rouen, trade unions from the Risle and the Eure Fishing Federation. They carry out research on fauna and flora of the river, if recolonization lead to the same plants and fish as before. And they monitor the water flow in the river and numerous springs. Their annual reports are very detailed and available online.

As the ponor was filled in it cannot be seen anymore. Nevertheless, during August its possible to see the decreasing amount of water in the river. We recommend a walk along the river. It's also possible to visit the Fontaine à Roger and other karst spring.