Multi-approach assessment of the spatial distribution of the specific yield: application to the Crau plain aquifer, France

Evaluación por múltiples aproximaciones de la distribución espacial del rendimiento específico: aplicación al acuífero de la llanura de Crau, Francia

Evaluation multi-approche de la distribution spatiale du porosité efficace: application à l’aquifère de la plaine de la Crau, France

Avaliação de multiabordagem da distribuição espacial do rendimento específico: aplicação no aquífero da planície do Crau, França

Pierre Séraphin (1) , Julio Goncalves , Christine Vallet-Coulomb (2) , Cedric Champollion (3)

1 GEOSCIENCES - Centre de Géosciences
2 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement
3 Géosciences Montpellier

Spatially distributed values of the specific yield, a fundamental parameter for transient groundwater mass balance calculations, were obtained by means of three independent methods for the Crau plain, France. In contrast to its traditional use to assess recharge based on a given specific yield, the water-table fluctuation (WTF) method, applied using major recharging events, gave a first set of reference values. Then, large infiltration processes recorded by monitored boreholes and caused by major precip- itation events were interpreted in terms of specific yield by means of a one-dimensional vertical numerical model solving Richards’ equations within the unsaturated zone. Finally, two gravity field campaigns, at low and high piezometric levels, were carried out to assess the groundwater mass variation and thus alternative specific yield values. The range obtained by the WTF method for this aquifer made of alluvial detrital material was 2.9– 26%, in line with the scarce data available so far. The average spatial value of specific yield by the WTF method (9.1%) is consistent with the aquifer scale value from the hydro-gravimetric approach. In this investigation, an estimate of the hitherto unknown spatial distribution of the specific yield over the Crau plain was obtained using the most reliable method (the WTF method). A groundwater mass balance calculation over the domain using this distribution yielded similar results to an independent quantification based on a stable isotope-mixing model. This agreement reinforces the relevance of such estimates, which can be used to build a more accurate transient hydrogeological model.

Mots clés: Numerical modeling; Water table fluctuation method; Specific yield; Geophysical methods

Domaines: Hydrologie

Pierre Séraphin, Julio Goncalves, Christine Vallet-Coulomb, Cedric Champollion. Multi-approach assessment of the spatial distribution of the specific yield: application to the Crau plain aquifer, France. Hydrogeology Journal, 2018, 26 (4), pp.1221-1238. ⟨10.1007/s10040-018-1753-y⟩. ⟨hal-01771484⟩