Lac de Montbel

Withholding located on the trireme, small stream tributary of the Hers-Vif, it is fed by the waters of the Vif-Hers brought by a Bypass located just downstream of the limit Peyrat-Ariège Aude département.
This can take the Hers a maximum flow of 10 m³ / s while the minimum flow let the river downstream of the intake is 1.2 m³ / s.

The water stored in winter and spring (snowmelt) are used for irrigation of the plain and Lauragais Ariège and the support summer flows and Fall of the Hers-Vif and beyond the Ariege and of the Garonne (ie the irrigation of 28,000 hectares).