Abandonment of gravity-fed irrigation: how to mitigate the impact on biodiversity and water cycle

For demographic, societal and climatic reasons, many countries have to manage changing agricultural territories and the evolution of these agricultural territories should accelerate by the global changes. In the Mediterranean area, traditional gravity-fed irrigation systems and associated channel networks are still widely used in agricultural territories. These systems affect landscapes and have had a lasting effect on the water cycle. Gravity-fed irrigation water contributes to the creation or maintenance of wetlands and contributes to the recharge of aquifers. A specific biodiversity is observed in irrigated areas and in areas crossed by irrigation canal networks. On the outskirts of urban centers, urbanization often extends over agricultural land, leading to an abandonment of gravity irrigation. In a climate change context, gravity irrigation may also disappear in favour of other more water-efficient irrigation techniques.

The current challenges therefore relate to:

- the identification of solutions to ensure the sustainability of channel networks and to mitigate the impact of the disappearance of gravity-fed irrigation perimeters.

- the implementation of these solutions by land planners.

We focused our work on a business area created within a sector where water from channels formerly used for gravity-fed irrigation is now used for watering green areas via a pressure network. This choice makes it possible to perpetuate the network of canals carrying water over the territory but some services initially provided by the irrigated perimeters such as the groundwater recharge or the reception of a specific biodiversity are no longer guaranteed there.

The atypical management of a stormwater retention basin, combining stormwater and irrigation water, has led to the creation of an artificial wetland that encourages the establishment of aquatic-dependent vertebrate animal species, including the unexpected presence of typical reed bed species. On the other hand, the invertebrate population remains sparse due to the rather irregular watering rate of the wetland.

Monitoring of water levels in this wetland shows that this basin leads to very large exchanges of water, both to groundwater and to the atmosphere, which can compensate for the flows disturbance induced by the abandonment of gravity irrigation.