Water Management for the 17th Century French Royal Canal of the “Two Seas”

Abstract

The Canal du Midi, constructed in the second half of the 17th century, was the largest public works construction project in Europe since the fall of the Roman Empire. The 240-km-long canal with a navigable depth of 1.8 meters [6 feet] and an average bottom width of about 13 meters [42 feet] overcame an elevation increase of 190 meters (625 feet) and was completed in less than 15 years to provide France with an internal route of water transportation from the Mediterranean Sea to the Atlantic Ocean. In addition to the manual excavation of the canal itself, the project required the construction of 328 separate structures, including 91 locks, and more than 200 bridges, dams, diversion structures, and tunnels. Producing a water supply near the summit to provide lockage water for both the Mediterranean and Atlantic sides of the canal was one of the greatest engineering problems encountered. The solution was the construction of Saint-Ferreol Dam, 780 meters [2560 feet] long and 32 meters [105 feet] high (second highest in Europe at the time). The dam created a reservoir that stored more than 6 million cubic meters (5,000 acre-feet) of water collected from diversion systems constructed in both the Mediterranean and Atlantic watersheds and could release the stored water in either direction through an ingenious two-gated basin near the summit as needed to augment natural flows entering the canal. Designated a UNESCO World Heritage Site in 1996, today the canal and its principal elements are a major scenic and recreational resource in southern France.