The Crau plain is located on the French Mediterranean coast, forming a triangle between Arles, Salon-de-Provence and the Gulf of Fos. Although it has no natural hydrographic network, it has benefited from surface water supplies thanks to the irrigation canals that have been diverting water from the Durance to supply the area since the 16th century. The formation of this plain is the result of successive alluvial deposits of the Durance over geological time. The sediments carried over were the result of rocks being ripped out of the Alps by the Durance, which, now a Rhône tributary, had the Crau area as its delta. The limestone in the run-off water precipitated onto the deposited alluvium, cementing it together and creating an impermeable substrate known as puddingstone. This layer of pudding formed a stony water table of variable depth (0 to 50 m, averaging 10 m) with a capacity of 550 Mm3: the Crau aquifer.