Le Suran

It immediately heads south1,2 , a direction it will maintain until its confluence with the Ain in the commune of Varambon near Pont-d'Ain5. In the valley, we hear people say: "at Varambon, the Suran loses its name".

The Suran is a fairly abundant river, as are all the rivers in the southern part of the Jura Mountains.
The Suran has very marked seasonal fluctuations in flow, as is often the case in eastern France, with high water in winter and low water in summer.

It should be noted that the bed of the Suran is completely dry during the summer months between the Bohas bridge and the Bourbou resurgence at Neuville-sur-Ain. Significant losses of flow begin upstream of the Marcou bridge (Simandre sur Suran), at the level of the Agnelou losses. In very dry years, the Suran is dry from Valuisant (Villereversure). This is a typical karstic phenomenon, the river flowing in a Jurassic and Cretaceous syncline made up of limestone. The Bourbou is a right bank resurgence, downstream of the Planche bridge (Neuville-sur-Ain). Downstream from this point, several resurgences in the river bed feed it. Part of the water of the Suran underground does not resurface at the Bourbou, but continues underground to reappear in the river Ain downstream of the Colombière (Grotte des Gaulois, resurgences near the Colombière, subaquatic resurgence off the spillway of the Grotte des Gaulois)