Sustainability of water transfers in the Crau plain

The Crau plain, 600 km2 located in South-East France, is mainly associated with the production of high quality hay (around 15,000 ha) irrigated from open-channel networks. Traditional irrigation practices consist in high discharge in order to reach the end of long plots, the excess of water being both drained by run-off to ditches and percolated to the so-called “Crau aquifer”. The aquifer recharge depends for around 70% on hay irrigation, the organization of its management thus relies on the sustainability of irrigation practices. However, hay production faces social and physical pressures from local to regional scales.

• Socially, water management in the fields requires to be fine-tuned to balance working time dedicated to irrigation (difficult labor conditions with high workload and night shifts) with water flows throughout irrigated plots, farms and canals.
• Physically, the low-performance hay irrigation is under tension because of local land-use changes due to the development of urban areas and other agricultural production (orchards and horticulture), in a context of hydraulic infrastructures requiring important rehabilitation works.
• Locally, return flows provide a mix of interdependent services, the aquifer being used for the extraction of drinking water for 300,000 inhabitants, for other irrigated crops like orchards, and for industries.
• Regionally, water comes from an historical inter-basin transfer, passing through a succession of hydraulic infrastructures and hydroelectric power plant before entering the plain. The climate change impacts on upstream precipitation make incoming water being less abundant, leading to water restrictions as experienced in 2022.

The sustainability of water transfers questions the integration of land and water planning. The aim of our research is to propose an original perspective coupling the characterization of water flows in relation to irrigation practices at the plot and scheme scales with the evaluation of farmers leeway in terms of economic and organizational constraints. The objective of this communication is to present each part of this work and to draw up further correspondences between the hydraulic and economic dimensions. First, an agrarian diagnosis revealed the lack of information on water flows, motivating in turn the original development of affordable measuring devices to track water in an irrigated block and automate parts of irrigation practices. Second, the context of water and land increasing scarcities motivated the characterization of the vulnerability of hay productions in terms of access to water, labor and markets. These studies aimed to directly contribute to water management in the Crau plain, respectively in the search for technical optimization to use water in the agricultural system more efficiently (contributing to reduce working flows) and for the definition and evaluation of strategies for adapting agriculture to meet the challenges of farm economics, groundwater recharge and water conservation. Finally, we will draw on both inputs to assess land cover scenarios and their impacts on aquifer recharge; we may also evaluate possible impacts of water restrictions on land uses.