The main reason for this tunnel are the #Jarrie and #Point-de-Claix chemical plant sites. The tunnel as dug is not enough to evacuate the entire #Romanche river in spring (when it's at it's highest levels), but gives enough leeway to have three days to evacuate those sites of chemicals before a burst dam could do damage. The Point-de-Claix site was recently in the news as #Arkema is leaving it behind, the Jarrie site has railroad-style warning lights for "Gaz Toxique" (toxic gases). Scary.