Groundwater flow dynamics of weathered hard-rock aquifers under climate-change conditions: an illustrative example of numerical modeling through the equivalent porous media approach in the north-western Pyrenees (France)

Jaunat, J.; Dupuy-Albarède, A.; Huneau, F.; Celle-Jeanton, H.; Le Coustumer, P.

Groundwater flow dynamics of weathered hard-rock aquifers under climate-change conditions: an illustrative example of numerical modeling through the equivalent porous media approach in the north-western Pyrenees (France) | Dynamiques des écoulements d’eaux souterraines d’aquifères de socle altérés dans des conditions de changement climatique: un exemple illustrative de la modélisation numérique selon une approche de milieu équivalent poreux dans le nord oust des Pyrénées (France) La dinámica del flujo del agua subterránea de los acuíferos de roca cristalina meteorizada bajo condiciones de cambio climático: un ejemplo ilustrativo de la modelización numérica a través del enfoque de medios porosos equivalentes en los Pirineos noroccidentales (Francia) 气候变化条件下风化结晶岩含水层地下水数值模型:(法国)比利牛斯山脉西北部通过等量孔隙介质方法数值模拟的实例 Dinâmica do escoamento das águas subterrâneas em aquíferos de rochas duras intemperizadas sob condições de mudanças climáticas: um exemplo ilustrativo de modelagem numérica através da abordagem do meio poroso equivalente no noroeste dos Pirineus (França)

2016

Jaunat, J. | Dupuy-Albarède, A. | Huneau, F. | Celle-Jeanton, H. | Le Coustumer, P.

A numerical groundwater model of the weathered crystalline aquifer of Ursuya (a major water source for the north-western Pyrenees region, south-western France) has been computed based on monitoring of hydrological, hydrodynamic and meteorological parameters over 3 years. The equivalent porous media model was used to simulate groundwater flow in the different layers of the weathered profile: from surface to depth, the weathered layer (5 · 10⁻⁸ ≤ K ≤ 5 · 10⁻⁷ m s⁻¹), the transition layer (7 · 10⁻⁸ ≤ K ≤ 1 · 10⁻⁵ m s⁻¹, the highest values being along major discontinuities), two fissured layers (3.5 · 10⁻⁸ ≤ K ≤ 5 · 10⁻⁴ m s⁻¹, depending on weathering profile conditions and on the existence of active fractures), and the hard-rock basement simulated with a negligible hydraulic conductivity (K = 1 10 ⁻⁹). Hydrodynamic properties of these five calculation layers demonstrate both the impact of the weathering degree and of the discontinuities on the groundwater flow. The great agreement between simulated and observed hydraulic conditions allowed for validation of the methodology and its proposed use for application on analogous aquifers. With the aim of long-term management of this strategic aquifer, the model was then used to evaluate the impact of climate change on the groundwater resource. The simulations performed according to the most pessimistic climatic scenario until 2050 show a low sensitivity of the aquifer. The decreasing trend of the natural discharge is estimated at about −360 m³ y⁻¹ for recharge decreasing at about −5.6 mm y⁻¹ (0.8 % of annual recharge).

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