The H+ network

The H+ network

Scientific context

The H+ research observatory is a network of aquifer observatories. Aquifers are defined as heterogeneous, porous environments in which deep water is circulating. 

H+ is composed of six sites located in France and India and representing different types of aquifers: basement aquifers in Ploemeur (France) and Hyderabad (India), carbonate aquifers in Poitiers and Larzac (France), and alluvial aquifers in the Allier plain (France). In addition to these sites, there is the laboratoire souterrain à bas bruit (LSBB, low-noise underground laboratory) of Rustrel, established in the limestones of Provence (a former military site of the Albion plateau) at a depth of 400 m. The climate – from oceanic to tropical – and land use – from agricultural to forest to peri-urban areas – are variable. The H+ observatory has the dual purpose of providing long-term observation chronicles of variables characterizing the groundwater resource and to be an experimental platform to study water and matter transfers in heterogeneous environments.


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Starting year: 2002

Localisations: Brittany, Allier, Mediterranean, India

Keywords: data-models, karst, water cycle


Web site:

PI: Olivier Bour

Scientific questions

The H+ observatory aims to measure and model water and matter fluxes in the heterogeneous deep porous environment of the critical zone. By encouraging the coupling between measurements, theories and models, its main objective is to improve predictive tools on water resources. The main scientific questions of H+ are:

  • What is the role of deep flows in controlling hydrological and biogeochemical cycles in the Critical Zone?
  • How to characterize the links between rainfall recharge, river-water table exchange, and deep water upwelling?
  • What is the age of the deep water?
  • How do water circuits in fractured environments influence the development of deep or surface living communities?
  • What is the architecture of the Critical Zone and how does it condition its response to human (e.g. exploitation), climatic or tectonic forcing?

Sites and measured variables

To answer to these questions, the H+ network sites use both long-term observation and experimentation (tracings, hydrodynamic tests). A certain number of variables are measured on a current basis: main hydro-meteorological variables, piezometric level of water tables, geochemical monitoring of major elements in solutio and 3D architecture.

The H+ network sites are:

Ploemeur Guidel Observatory

The Ploemeur Guidel observatory is located in Brittany and is made of two sub-sites: the Ploemeur site (Morbihan) and the Guidel site. Ploemeur is an aquifer, exploited since 1991 and benefits from an oceanic climate, located in a fractured crystalline domain. It provides 1 million cubic meters per year for the supply of drinking water, permanently pumped for the town of Ploemeur, of nearly 20,000 inhabitants. The Guidel site is similar to the one of Ploemeur, but is not exploited because it is located in a coastal wetland, classified as Natura 2000.

Larzac Observatory

It is located in the region of the Grand Causses, south of the Massif Central. The karstic aquifer of Durzon represents a surface of 100 km² which feeds the spring of Durzon. This spring supplies the drinking water of the Aveyron part of Larzac. The observatory has a set of sites dedicated to gravimetric, inclinometric and hydro-geodesic observations, as well as a flow tower for evapotranspiration measurements.

The Poitiers Experimental Hydrogeological Site

This observatory is located 2 km east of the Science Campus of the University of Poitiers. The experimental device includes 35 boreholes more than 130 meters deep, spread over a dozen hectares and built between 2002 and 2004. These boreholes cross the entire Dogger aquifer, most of them are located in a regular grid in a 210 m*210 m square. The piezometric levels vary in normal regime between 15 m and 25 m in relation to the ground surface.

Auverwatch Observatory

It is focused on the alluvial water of the Allier River, one of the main tributaries of the Loire (1,000 km long), which extends over a catchment area of more than 14,000 km² and plays a fundamental regional role from a socio-economic point of view (drinking water, agricultural development), but also ecological, as the Allier is an integral part of the Loire River basin.

Baget Observatory

The baget watershed (13.25 km2) is a mountain ecosystem located near Saint-Girons in the Ariège. It is a mid-altitude mountain ecosystem (about 1,000 m) drained by a karstic network that feeds the surface flow of the Lachein stream basin of the Garonne. This karst basin has been monitored since 1968 for hydroclimatic parameters, including air temperature, precipitation and stream flow. The monitoring system consists of a main weir at the outlet, 3 complete excess controls, 3 piezometers, one in the abyss and one in the underground loss.

Low noise underground laboratory

Located in Rustrel in the Vaucluse, in the Luberon regional nature park. The site is at the heart of the karstic massif of the Fontaine de Vaucluse. It consists of more than 4 km of galleries up to 520 m deep, under a total surface of ~500,000 m², offering a unique access to the unsaturated zone (UZ) of the Vaucluse Fountain basin. The site also includes five 21 m long, 146 mm diameter core drill holes, 280 m below the ground surface.

Hyberabad Observatory

It is located in South India in an altered and fractured crystalline aquifer subject to strong anthropic pressures (pumping, inputs, etc.) induced by agricultural practices. It includes two sites, Choutouppal (Andra Pradesh, South India) of an area of 43 ha and in which an artificial recharge has been set up, and Maheshwaram, a rural watershed heavily exploited for irrigation (nearly 1,000 water boreholes over 50 km²).

Mallorca Observatory

The Mallorca Observatory is studying a site located at Ses Sitjoles (12,000 m2), south-east of the island. This is a very permeable carbonate reef aquifer (Miocene), with a few karstic cavities on a metric scale. In this area, intensive agriculture and irrigation cause overexploitation of the phreatic zones, which results in the intrusion of saline water up to 15 km into the island, and therefore the pollution of the phreatic zones with chloride. The site is comprised of a network of 12 deep boreholes (100 m), 7 of which are fully cored, spread over an area of 1 ha.

Partners and further information

The H+ network is an observation service labelled by the CNRS. It brings together several CNRS-University-INRAE laboratories: Géosciences Rennes (coordinating UMR), the Institute of Chemistry of Environments and Materials of Poitiers (IC2MP), Géosciences Montpellier, the Mediterranean Environment and Agro-hydrosystems Modeling Laboratory (EMMAH), the Besançon Chrono-Environment Laboratory, the Geosciences Azur Laboratory, the LSBB and the Bureau de Recherches Géologiques et Minières (BRGM). The foreign partners are the National Geophysical Research Institute (NGRI, India), the Consejo Superior de Investigaciones Científicas (CSIC, Spain) and the Forschungszentrum Jülich (Germany).