Experiments in Hydrology and Hydrogeology (LETH2)

The Laboratory for Hydrology and Field Hydrogeology Experiments (LETH2) responds to the needs related to experimental developments in this field, whether on site or in the laboratory. Since 2009, the laboratory has evolved to integrate new works conducted in geomorphology and surface hydrology. This partly involves measuring the flow of water and sediments using velocimetry, optical and acoustic turbidity measurements, and partly involves measuring the evolution of topographic surfaces driven by rapid erosion processes.

High-frequency experiments of dissolved gases to characterize groundwater inflow in a Natura 2000 classified pond
  1. Field of activity
  2. Technical projects
  3. Projets scientifiques
  4. Equipment managed by LETH2
  5. Scientific and technical collaborations
  6. Members

Field of activity

The laboratory is specialized in the field of experimentation and on-site monitoring. It provides support to technical and scientific projects. The works of the laboratory include work in electronics, chemistry and mechanics with, specifically, the development of new instrumental tools or innovative measurement methods.
On-site work includes physico-chemical measurements and drilling experiments (tracing, pumping tests, geophysical and flux imaging), as well as hydrological monitoring of National Observation Service sites (H + and AgrHys).
In the near future, one of the laboratory’s objectives will be to improve the quality of the measurements. Specifically, a metrology project focusing on pressure sensors, temperature sensors and experimental tracing tests will start in 2010.

Technical projects

  • Technical project on the *dating of groundwater*: this technical project was set up by L. Aquilina and T. Labasque, as part of a thesis focusing on the implementation of an analytical protocol for dating groundwater, via the analysis of CFCs, SF6 and rare gases in solution. This project has also led to the creation of a company by the PhD student concerned (V. Ayraud) and the implementation of this specialized service in the analysis of dissolved gases.
  • PIVEF project entitled “Development of a probe to measure flow velocities during drilling*”. This ongoing project, which will incorporate a thesis work (S. Ruelleu, 2010), is being carried out in collaboration with INSU's Technical Division. Its objective is to develop a probe to measure flow velocities during drilling based on particle image velocimetry (PIV). The tool consists of an underwater CCD camera for which the vertical position in the probe is controlled by a motor with micrometric movement. Since April 2004, the date of the project start, the probe was developed and then tested on a test bench, prior to performing the first tests on site.

Projets scientifiques

  • National Observation Service H+* (2002-present, leader: P. Davy): Hydrological, hydrochemical and climatic monitoring of the Ploemeur site (56). The key components of this project are the implementation and testing of sensors, the transfer and processing of data, taking samples and sample preparation. In addition, the laboratory was very involved in flow imaging experiments, and especially tracing experiments, particularly those carried out in collaboration with University Bochum, Barcelona and Lausanne.
  • Environment Research Observatory (Agryhs ERO)* (2002-present, leader: P. Mérot) Participation in field campaigns and the hydrochemical monitoring of the Kerbernez site (29). Application of water dating methods.
  • ANR (French National Research Agency) Vulnerability: Environments and Climates project* “MOHINI, Integrated modeling of water resources in bedrock aquifers: vulnerability to human induced global change” (2008-2011, coordinator H. Pauwels (BRGM). The laboratory is primarily involved in hydrological and hydrochemical monitoring and in carrying out reactive tracing tests.
  • Regional PRIR DATEAUX project* (2003-2007, leader: L. Aquilina): To measure the residence time of water using geochemical methods, the laboratory has specifically emphasized the development of the analysis of gases that are dissolved in groundwater using Chromatography as well as the development of tools to interpret the biochemical processes and recharge mechanisms of aquifers (Temperature, excess air).
  • 3D-VEROS project (2009, leader: D. Lague): *Measurement of erosion rates using the Terrestrial Laser Scanning (TLS) technique*. We are one of the few research units to have a Terrestrial Laser Scanner, and we are currently working on using this tool to detect centimetric variations in the topography linked to erosion/sedimentation processes, or to soil deformations in very diverse environments (Bay of Mont St. Michel, a torrential river in New Zealand, cliffs in Brittany, etc.).

Equipment managed by LETH2

  • Borehole log: Gamma Ray, Heat Pulse Sensor, Temperature/Conductivity Sensor, Propeller flow meter,
  • Submerged borehole pumps
  • Multi-parameter borehole sensors (pH, Eh, Conductivity, Temperature, O2, dissolved gas)
  • Borehole fluorometers
  • Resistivity sensor
  • Borehole packers
  • Piezometric sensors (STS, DIVER, Paratronic, etc.)
  • Manual borehole samplers (up to 150 m)
  • Nitrate, turbidity and dissolved organic carbon borehole sensor (SCAN)
  • Turbidimeter ASM-IV rod
  • Vector ADV
  • Acoustic flow meter


Hydrochemical sampling - © Nicola Lavenant

Scientific and technical collaborations

DT INSU (Technical Division), INRA, UMR ECOBIO, H+ ERO, AgrHys ERO, etc.

LETH2 collaborates within OSUR on scientific and technical projects related to observation or experimentation. It is integrated within the Support Department of OSUR’s Observation Services (S3O) of OSUR

Measurement of the flow in a river - © Nicolas Lavenant