The ORACLE observatory includes various scientific equipments in order to carry out hydrological, hydrogeological, chemical, meteorological and pedological measurements.
- Limnimetric stations
All ORACLE limnimetric stations (10 stations) are equipped with a weir (rectangular- or triangular- profile weir) and with a reference staff gage. Each station is provided with a float gage backed up with supersonic echo sounder placed in a stilling well connected with the river, to avoid all disturbances during measurements. Stage measurements, in the various considered streams, are recorded and remotely transmitted to the manager of the ORACLE metrological park. Rating curve is carried out and updated from regular gauging carried out at each station. Rating curve points and continuous stage measurements (every hour and every 5 minutes in flood period) are recorded on the national hydrometric data bank (banque HYDRO), managed by the Ministry for Ecology and Sustainable Development.The 10 limnimetric stations of ORACLE are able to measure flow values ranging from 0.01 to 1000 m3/s with an average error of 5%.Spatialization of flow measurements is representative with spatialization of Strahler orders met on ORACLE. A flow measurement is carried out on outlet of each ORACLE sub-catchment.
- Precipitation stations
Rainfall data are acquired via 9 precipitation gages with rocking troughs, all equipped with a recording system and remote-transmitter DANAE/RTC and DANAE/GSM (Alcyr). Rain falls into a receptacle and runs out in one of the two compartments of the rocking trough. When water of one of the compartments reaches 0.2 mm, trough rocks and the second compartment is set up under the receptacle. Each tilt of the trough is recorded. After recording, water flows in the lower part of the trough and is recovered by a gauge bucket.
Audit and maintenance process of the precipitation gages was set up at INRAE. A mechanical and electric control, as well as a measurement test is carried out annually.
An semi-automated procedure is used for validation of rainfall measurements. The comparison between bucket measurements and measurements acquired by the precipitation gage constitutes a first data validation. Each period of measurement of a gage is also compared with total measurements taken on the other precipitation gages over this same period. Lastly, measurements are also compared with the lower and higher quartiles calculated from rainfall measurements since 1962. Average error of rainfall measurements is about 10%.
Spatialization of precipitation stations results from a good knowledge of runoff distribution studied since 1962 on ORACLE. Moreover, rain measurements are also taken through the SAFRAN grid set up by Meteo-France.
- Piezométric stations
A set of piezometric stations (piezometers and well) make it possible to study the hydrolic grade line of the two ORACLE aquifers (Brie and Champigny aquifer). On each one, piezometric probe was installed (Diver from SDEC and CTD from OTT).
Currently, data are validated by intercomparison between the variations of hydrolic grade line and rainfall events of the Observatory. Precision of piezometric measurements is of ± 0,05%, with a resolution of 0.01% (value of the probes manufacturer).
Even if there is a piezometric station for each Orgeval sub-catchment, there is a principal transect of piezometer (7 piezometers from 10 to 30 m of depth), localized on the Avenelles sub-catchment and installed by the Ile-de-France Federation of Research in Environment (FIRE) during the year 2008.
- Water sampling
On the observatory, water quality is monitored through rain, surface and drainage waters, but also through water table and source water.
Surface waters are sampled using automatic samplers every 24 hours. Other water samplings (rainfall, water table, source, drains) are carried out manually and weekly by the technician of research. All samples are stored on the INRAE site (Boissy-le-Châtel) at 4°C before being conveyed to the Chemistry laboratory (INRAE –Antony) which follows a quality step and guarantees measurements reliability.
All samples are analyzed by continuous flow automated spectrophotometry (Quaatro39 from Seal Analytical) for NH4, NO3, NO2, PO4 and chlorides concentrations. Dissolved organic and inorganic carbon are also analyzed using a TOC analyzer (TOC-L CPN from Shimadzu). Conductivity is measured directly using a conductimeter (WTW LF 538).
Spatialization for the water quality is representative of the discharge measurements (Strahler order) and takes place at each outlet of the observatory sub-catchment. Measurements of surface waters qualities allow us to evaluate the discharge of agricultural, forester and mixed sub-basins.
- Meteorological station
Complete meteorological station, managed by INRAE since 1962, and two stations managed by Meteo-France are located on the Observatory or in close vicinity.
Part of INRAE measurements is today remotely transmitted to Meteo-France which returns validated data. Meteo-France provides besides validated data, calculated data of potential evapotranspiration (PET). Validation is done here by intercomparison with data of the two closest meteorological stations.
- Soil moisture stations
Soil moisture measurements, on several depths in the same site (11 depths from 5 to 155 cm) are acquired by a method of reflectometry (TDR-Trase from Sols-Mesures). Soil moisture measurements of the surface (0-5 cm of depth) are acquired by “Theta” probes (ML2X from Sols-Mesures) which give a median value of moisture, always by reflectometry, on the whole length of the electrodes (5 cm).
These methods make it possible to measure moistures with a resolution of 1% and a measuring accuracy of ± 3 % (values of the manufacturer). Currently, there exist three points of soil moisture measurements by TDR, located on the ORACLE observatory (Orgeval catchment area, in the north of the Petit Morin catchment and in the south of the Grand Morin catchment). Three measuring sites of surface soil moisture are located on the Grand Morin catchment.