Recharge des aquifères

Résumé

La recharge des aquifères ou infiltration résulte naturellement d'un processus hydrologique par lequel les eaux de surface percolent à travers le sol et s'accumulent sur le premier horizon imperméable rencontré (banc d'argile ou de marne) ; elle peut aussi être assurée artificiellement par des puits filtrants. Ce processus s'amorce généralement à partir de la zone vadose, sous la pédosphère où les racines des végétaux captent encore l'essentiel de l'eau interstitielle. La réalimentation est caractérisée par le débit de filtration alimentant le toit de l'aquifère. Le processus Principaux mécanismes Les nappes aquifères sont naturellement réalimentées par les précipitations et fonte des neiges et, à un moindre degré, par les écoulements de surface (rivières et lacs) ; mais cette réalimentation peut être affectée par les activités anthropiques comme l'imperméabilisation des sols, les défrichements ou l’exploitation forestière : elles s'accompagnent de la destructio

Source officielle

https://fr.wikipedia.org/wiki/Recharge_des_aquif%C3%A8res

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Fonctionnement et gestion des aquifères alluviaux de haute altitude

The Haute Sarine alpine valley is located at an average altitude of approximately 1'000 to 1'200 masl. It was formed in its southern part up to the area of Gstaad to the favour of a typical North-South tectonic fault according to the main structures of the Préalpes, then followed normal fault striking East-West to end up on the rock bolt of the Vanel hill. The late and postglacial period was marked by the deposition of glaciolacustrines, glaciofluviatile and flurecent fluviatile sediments which have filled the ice free valley bottom probably starting from a period older than the Bölling-Alleröd interstadial. The depth of this overdeepening varies between 20 and more than 50 m of depth. Drillings which we carried out could document series of typical glaciolacustrine sediments. The implementation of several geophysical survey methods (resistivity, seismic refraction and reflexion, well logs and pumping tests) enabled us to analyse several sources of information which we confronted between them in order to produce a 3D model of the quaternary deposits and their hydrological properties. Most of these sediments are relatively quite permeable and build a free groundwater reservoir that we subdivided into 3 parts. The basin of Gsteig in the south is closed, the valley having been blocked by a massive landslide that probably occurred in several successive stages starting at the first climate improvements. The second part, the basin of Feutersoey has not been retained as a potential important hydrogeologic resource based on our preliminary investigations. The last basin, that of Gstaad-Saanen is the largest and thickest. It is also in this basin that most of the tourist and industrial activities of the area are concentrated. The observation network was established in order to characterize the groundwater flows enabling us at the same time to carry out piezometric measurements and chemical as well as and bacteriological analyses. We also carried out a δ18O isotope analysis campaign. The whole of these approaches highlighted the particular characteristics of the groundwater recharge. The groundwater system is mainly fed by the Sarine and the precipitations infiltration. We also located an underground karstic feeding of evaporitic type. We finally propose a groundwater management and protection concept adapted to the particular situation of the Sarine alluvial mountain aquifer system on both quantitative and qualitative aspects. The high altitude alpine groundwater catchment areas such as the Haute Sarine represent as a whole a quality resource, with high potentials yet to be defined on a larger scale, for example by applying numerical modeling and by organizing and maintaining long term observation networks that will enable us to define a sustainable groundwater resource management within the alpine area.

EPFL2000

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Snow cover variations and spring snowmelt runoff modelling in the source region of the Yellow River, China

Léo Zhou Ficheux

This study aims to assess the snow cover spatial and temporal variation in the Source Region of the Yellow River, to understand the effect of snowmelt on the hydrology and to evaluate the potential impact of increasing temperature on the spring snowmelt runoff. The Snowmelt Runoff Model (SRM) developed by Rango and Martinec was used and improved by adding diurnal temperature computation and snow storage computation to model the runoff for 2013, 2014, 2016 and 2017. The snow cover assessment was done using Tera-MODIS satellite images between 2001 and 2017. Results showed that spring snowmelt produces 38% of direct runoff before July and 15% of annual runoff in average. The snow cover is very sensitive to temperature and to winter precipitation. There is a significant decrease of snow cover in May since 2001 in parallel to a significant increase of temperature. The snow cover duration has decreased by more than 15 days (20%) in the permafrost area in 15 years. Simulation suggests that a temperature increase of 2°C or 4°C will reduce the spring snowmelt by at least 20% and 30% respectively, and spring peak runoff will occur up to 15 days and one month earlier. Future investigations should focus on the interaction between snow, frozen ground and ground water recharge in order to extend the knowledge on snowmelt impact to soil related processes which play a key role on the ecosystem degradation in the region.

2018

Chargement

Assessment of available water is the basis that allows for sustainable management of the water resource. Special need concerns the assessment of groundwater resources, about which, often little is known. The present study aims to explore the water resource, with a focus on groundwater, of a small catchment (3.5km2), situated in a semi-arid zone in Burkina Faso (West Africa). A 5-year data set of stable isotopes of water, groundwater level and other hydrologic data is used to gain insight into the water resources in this small catchment. The main effort is devoted to the analysis of isotope data, with the secondary goal to asses the potential of the use of stable isotopes of water as an innovative tool in hydrology. Analyzed are temporal and spacial variations of the isotopic signature in groundwater, surface water and rain. Isotope data is compared to groundwater level data. Isotope data allowed to distinguish two different categories of wells. First, wells where evaporation dominated compared to recharge at the end of the wet season through the dry season, and wells that have constant isotope ratios throughout the year. Evolution of the isotope signature of the former suggests that these wells get disconnected from the aquifer at some point of the year. Comparison of isotope ratios of different sampling sites (springs, wells, pumps, surface water and rain) revealed that the upstream springs diverge from the other sites in their isotopic signature, and thus either have a different origin or were subject to different processes. Negligible diurnal variations observed in isotopic signatures of wells prompt that diurnal fluctuations observed in groundwater levels are due to non isotope fractionation processes. Periods deduced from seasonal changes in isotopic signatures match periods of rising and decreasing groundwater levels. Though groundwater levels show inter-annual variability, especially in their peak levels, this was not reflected in the isotope data. Isotope data confirmed conclusions gained from other data (recharge periods), added additional information (diurnal fluctuations of wells are non isotope fractionation processes), and pointed out the fact that upstream spring water distinguishes in some form or another from other groundwater.

2014

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Fonctionnement et gestion des aquifères alluviaux de haute altitude

EPFL2000

2014