Nouvelle-Aquitaine – Amplifying the role of groundwater in wetlands

RAMAGE

Recharge Annuelle et Maintien Alluvial de la Garonne en Etiage en Lot-et-Garonne (Annual Recharge and Garonne’s Alluvial Maintenance at Low Level in Lot-et-Garonne)

Type of landscape : Rural Landscape

Ecosystem

The project is located in Lot-et-Garonne on the portion of the river bordered on the left bank by the Garonne canal. Three major study areas are located between Agen and Marmande and Tonneins.

The geological characteristics make artificial recharge a very interesting strategy to support the flow of the river during periods of low water, with the infiltrated water returning directly to the surface flows. In this sector of the Garonne valley, 65 % of the volumes of water withdrawn contribute to agricultural diversity (around 70 sectors present) the rest is mainly used for domestic uses and gravel pits exploiting the major bed of the river. We can note that the study is located in the Mazière National Nature Reserve and the Natura2000 zone.

For further information: SMEAG – Syndicat mixte d’études et d’aménagement de la Garonne

Introduction

In Nouvelle-Aquitaine, the water management process in the Garonne basin will build on a range of solutions to increase the natural and artificial recharge of surface waters in relation to rivers, to limit the decrease of low water flows during summer and to generate thermal dilution of surface waters, also testing the societal acceptability of groundwater recharge techniques.

Water availability is a prominent challenge. Droughts have reached historical levels in 2022, affecting water supply for agriculture and human consumption. Management of the water resource is key to allow access for all users. In the Garonne River basin, water scarcity has been increasingly extending beyond the summer. Economically viable and socially acceptable solutions for artificial recharge of rivers, water bodies and groundwater are being investigated.

In the Garonne River basin, the demonstration focuses on a mature solution to implement artificial recharges of the local water table. How to increase water resources through artificial recharge? What are the actual benefits from water re-use? The goal is to use the property of the soil to store water to release it during the summer period and support low flows. The public body in charge of monitoring and managing the Garonne River basin is a central actor. Local communities are involved from the beginning, as their understanding and acceptance of groundwater recharges is crucial for the project sustainability.

Specific NbS tailored for the Nouvelle-Aquitaine Region

Promote the potential for infiltration of surface water from the river into its alluvial table to reinforce natural low flow support.

Pilot Description

The project aims to experiment with the possibility of recharging the alluvial aquifer of the Garonne in order to support low water levels of the Garonne during the summer period. Indeed, in the absence of rain and contributions from the snow melt in the Pyrenees, the main contribution of the Garonne is through its accompanying layer. The objective of the project is to study the feasibility of recharging the Garonne aquifer, during bad recharge years, in order to help support the flow rates of the Garonne at low water levels. The final objective of this project is to infiltrate between 8 to 10 hm3 into the Garonne aquifer in the Tonneins sector.

Environmental Challenges

The project aims to support the Garonne River flows with cooler water in summer to contribute to the overall improvement of water quality as well as to maintain the hydraulic connectivity of the river both with its alluvial water table and with its annexes, wetlands which provide refuge and ecological corridor functions for biodiversity. This project looks forward as well to improved knowledge of groundwater biodiversity.

Policy Support

The project is part of the recommendations of the Adour-Garonne Water Development and Management Master Plan (SDAGE), the Climate Change Adaptation Plan (PACC) voted by the Adour-Garonne basin committee in July 2018 and themes listed in the Agreement for water in the Adour-Garonne basin signed in October 2018 between the basin coordinator prefect, the basin committee and the two prefects of the Nouvelle-Aquitaine and Occitanie regions.

This project responds to various measures of the SAGE (water development and management plan) Garonne Valley’s EMP (low water management plans): Raise awareness of the importance of living soils and encourage the limitation of runoff by promoting infiltration and retention of water in the soil; improve knowledge of aquifer-river relationships and aquifer recharge; and improve knowledge of groundwater.

Expected impact of NBRACER

The NBRACER project will allow to explore new infiltration points along the Garonne River and to do a larger scale infiltration tests. Citizen’s awareness and communication is going to be also held during the project in other to increase acceptability.