Gravity irrigation technique

Gravity irrigation in Crau involves allowing water to flow over flat or slightly inclined land so that it slowly infiltrates into the soil. This centuries-old technique submerges entire meadows every summer, recharging an underground aquifer that provides drinking water for hundreds of thousands of people in the Provence region.

Aquifer recharge and seasonal variation

According to reports, the gravity irrigation of Crau meadows ensures between 66 and 70% of the annual recharge of the Crau gravel aquifer, with rain providing the rest. The aquifer, estimated at 550 million cubic meters, functions inversely to typical Mediterranean aquifers, with high water levels in summer and a decrease in winter.

Historical irrigation infrastructure

The Craponne canal, an engineering work dug in 1559 to divert water from the Durance river to the arid plain of Crau in the Bouches-du-Rhône department, is central to this system. Nearly five centuries later, the principle still functions, almost without modification.

Modern canal network

Today, a network of about 400 kilometers of canals covers the plain, with water from the Durance still flowing through them following the same gravity-based logic inherited from the 16th century. This hydraulic network is not a folkloric relic; it still structures agricultural economics and the water supply of an entire region.

Crau hay and irrigation

Crau hay, recognized by a protected designation of origin, is the emblematic production of this plain. Each spring and summer, from late March to late September, farmers deliberately flood their meadows. This act, which could seem counterproductive for a forage crop, is actually at the heart of the system.

Water infiltration and aquifer management

By allowing water from the Durance to cover the fields, farmers not only irrigate their hay but also inject a significant amount of water into the gravelly soil of Crau. This water slowly percolates through the gravel and eventually reaches the underground aquifer, several meters below the surface. The Symcrau, the mixed authority managing this aquifer, has quantified this phenomenon.

Significance of the aquifer

The Crau gravel aquifer is not a simple anecdotal reservoir. Its volume is estimated at 550 million cubic meters by the Symcrau, a figure that gives an idea of the scale of this hidden underground water stock beneath the plain's gravel. This reserve supplies drinking water to approximately 270,000 people according to documents from the aquifer contract, a figure that the AFP also mentioned around 300,000 people in 2023.

Impact of irrigation on aquifer levels

In both cases, the number refers to a significant population, well beyond the agricultural villages of the plain. The amplitude of the aquifer level variations clearly illustrates the influence of irrigation. In non-irrigated areas, the level changes by about 50 centimeters over the year. In irrigated areas, this variation can exceed 10 meters.

Management concerns and interdependence

This dependence explains why the Symcrau is cautious about agricultural changes. Reducing the irrigation of meadows for economic or water management reasons could endanger the balance of the entire plain, according to statements from the syndicate reported by AFP. The Symcrau, a public institution created in 2006, has managed the Crau aquifer contract since 2016 to try to reconcile agriculture with drinking water supply.

Unique water supply relationship

This situation reveals an interdependence rarely seen elsewhere: residents who drink water whose availability directly depends on an agricultural practice inherited from the Renaissance. Crau hay is therefore not only a protected local product. It is also, without most tap users realizing it, an essential component of their water supply.