Présentations Colloques

Oral Presentation
7.07
Session 7.07: Transdisciplinary and participatory approaches in groundwater research and management
Bardeau Mélanie - Le Cointe Pierre
Managing groundwater extraction for irrigation in Tarn-et-Garonne (France)
In France, in one of the watershed districts from the European Water Framework Directive, the Adour-Garonne basin, alluvial aquifers make for strategic water resources thanks to their high productivity, their accessibility and their low providing costs. Therefore, they are highly exploited for agricultural irrigation. These aquifers are closely linked to the rivers and support their low flows. Since several decades, lower rainfall has led to more severe low flows, which created conflicts of use. The need for a groundwater extraction management tool arose for local water authorities (DDT). As an example, in 1995, the BRGM was asked to build a hydrodynamic model of the alluvial aquifer in Tarn-et-Garonne. 940 kmC divided in 5 alluvial terraces crossed by 3 main rivers (Garonne, Tarn and Aveyron) were modeled with MARTHE (BRGM software). The first model ran in steady state on a 1x1 km grid. The study area was divided in several spatial units and a simplified groundwater extraction management tool with EXCEL was developed. From 1997, DDT has used this tool to manage groundwater extraction for irrigation in each spatial unit. In 2007, the model has been updated to run in transient state with a refined mesh (250x250 m). In 2016, a second update has been launched- the model now has two layers and 36,500 cells+ it simulates the water level and flow of 41 rivers in a 20-year span and takes into account 750 agricultural pumping wells. The updated management tool integrates the Allowed Pumping Volume and Unique Authorization Over Several Years notions and the new French legislation with water management driven by “Organismes Uniques” based on watersheds rather than administrative breakdown. A participative forecasting study, combining the scientific approach with the farmers’ and the territorial actors’ point of view, was also carried out to model the quantitative management of groundwater resources in France around 2020-2035.
France