The H+ network

The H+ network

Scientific context

The H+ research observatory is a network of aquifer observatories, considered as heterogeneous porous environments in which deep water is circulating. H+ is composed of six sites in France and India sampling different types of aquifers: basement aquifers in Ploemeur and Hyderabad in India, carbonate aquifers in Poitiers and Larzac, and alluvial aquifers in the Allier plain. In addition to these sites, there is the laboratoire souterrain à bas bruit (LSBB) de 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 twofold vocation 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.


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. y encouraging the coupling between measurements, theories and models, its main objective is to improve predictive tools on water resources. The main scientific challenges of H+ are:

  • What is the role of deep flows in controlling hydrological and biogeochemical cycles in the critical zone?
  • How 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 Pour répondre à ces questions, les sites du réseau H+ utilisent à la fois l’observation sur le long terne et l’expérimentation (tracings, hydrodynamic tests). A certain number of variables are measured on a recurrent basis: main hydrometeorological variables, piezometric level of water tables, geochemical monitoring of major elements in solution, 3D architecture.

The H+ network sites are:

Observatoire de Ploemeur Guidel

Ploemeur Guidel Observatory

The Ploemeur Guidel observatory is located in Brittany and is made up of two sub-sites: the Ploemeur site (Morbihan), an aquifer that has been exploited since 1991 and benefits from an oceanic climate, located in a fractured crystalline domain.It provides 1 million m3 per year for the supply of drinking water, which is permanently pumped for the town of Ploemeur, which has nearly 20,000 inhabitants, and the Guidel site is similar to that 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 in the 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 in a natural way. The observatory has a set of sites dedicated to gravimetric, inclinometric and hydrogeodesic observations, as well as a flow tower for evapotranspiration measurements.

The Poitiers Experimental Hydrogeological Site

Located 2 km to the east of the Science Campus of the University of Poitiers, the experimental device includes 35 boreholes of more than 130 meters in depth spread over a dozen hectares and built between 2002 and 2004. These boreholes cross the entire Dogger aquifer, most of them being 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 table of the Allier River, one of the main tributaries of the Loire (1000 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 1000 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 certain hydroclimatic parameters, including air temperature, precipitation and stream flow. The monitoring system consists of a main weir at the outlet, three complete excess controls, three 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 in 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 deep, 146 mm diameter core drill holes, 280 m below the ground surface.


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) with 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 1000 water boreholes on 50 km²).

Partners and further information

The H+ network is an observation service labelled by the CNRS. It brings together several mixed 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 Agrohydrosystems 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).