Data base

Currently, all data collected by Irstea is available from the Orgeval basin manager (alain.guerin@irstea.fr). It is directly available from this site via BD_ORACLE©.

The scientific aim of ORACLE is the hydrological and biogeochemical functioning of sedimentary basins, in a rural anthropized environment. Multivariable and multi-scale observations of embedded catchments(1km² à 1800 km²)of the Paris basin are necessary for this research.
ORACLE provides the scientific basis necessary for management and control of risks related to extreme events (floods, droughts) and to anthropic impacts on streamflow and water quality, with a particular focus on agricultural activities. Anthropisation also contributes to increased risks and vulnerability of geographical areas. Only observation, with adapted width and duration, on various scales, from agricultural plot to catchment area, can answer these challenges.
ORACLE is made up of the “Petit Morin” and “Grand Morin” basins (Figure 1). The Morin rivers are the two principal tributaries of the Marne River. They have a direct influence on the flows, going from the Marne to the Seine until the Paris conurbation. The Orgeval catchment, observed since 1962 by Irstea is a sub-catchment of the “Grand Morin” basin (Figure 1). The Morin basins are primarily agricultural (80% agricultural, 15% forester, 5% urban), and consistent with field crop regions. Ground cover has remained relatively constant since it is under observation.

Carte 1 - Observatoire de Recherche du GIS ORACLE: Bassins versants du Grand Morin, du Petit Morin et bassin versant de l'Orgeval.

Map 1 – Research Observatory of GIS ORACLE: Grand Morin, Petit Morin and Orgeval catchments.

 
ORACLE, located on the Brie plateau (Brie limestones, lower Stampien), is covered by a quaternary loess deposit (up to 10 m thick). The upper layer is constituted of loess silt and the lower one is enriched in clay and sand. This silty glossic leached brown soil is characterized by low permeability resulting in temporary waterlogged soil in winter, and the presence of a perched aquifer. Soils are naturally poorly drained. Subsurface drainage (actually 60% of the territory) has been installed starting in the 1960s. Brie limestones (lower Stampien) constitute in a first aquifer of low depth (10 to 20 m), mainly fed by infiltration on the Brie plateau. It is an unconfined aquifer very vulnerable to agricultural pollution, because of an almost total absence of a roof protection. Brie limestones are separated from Champigny limestones (Ludien, upper Eocene aquifer, 20 to 30 m thickness) which level on valley sides, by green clay and supra-gypseous marls, a practically impermeable formation with variable thickness (8 to 22 cm). Champigny limestones constitute an aquifer with permeability and cracks, supplied by the valley sides, the porous zones and the pits. This aquifer is vulnerable near valleys. Limestones of Saint-Ouen, ORACLE deeper formation, form confined water, with infra-gypseous marls roof, which takes part in the supply of the Grand Morin river when it is not surmounted with alluvia (Coulommiers – Pommeuse). This aquifer becomes vulnerable when limstones of Saint-Ouen sub-level under the alluvia. The whole of the hydrological and hydrous compartments of ORACLE area are followed via a complete network of measurement: limnimetric stations at each outlet sub-catchments and in the drainage network, piezometric stations, precipitation stations distributed on the whole of ORACLE area and stations of grounds moisture in surface and in-depth. This device is doubled with a network of water quality measurement for surface run-off, rain and the water-table.
A network of « de basic » measurement is maintained permanently on ORACLE, in order not to stop chronicles. Length and continuity of certain time series on the long run are necessary to i) correctly apprehend hydro-systems operation, ii) detect tendencies or changes in behaviour, iii) evaluate impacts of anthropic origin, from vegetation cover to hydro-agricultural installations in changing climatic conditions.

This basic data is acquired mainly by the DIREN Ile-de-France, Meteo-France and Irstea (Table 1).

 Table 1 : ORACLE Data base
 
Equipements
Types of measurement
Number of stations
Frequency
Duration
Limnimetric Stations
Water level / punctual gauging
11
Continuous
Since 1962 for some
Pluviometry
Precipitation gages with rocking trough
19
Continuous
Since 1962
Piezometry
Manual or piezometric probe
11
(2 to 40 m of depth)
Continuous for some or weekly
Since 1989
Water sampling
NO3, NO2, NH4, PO4, Cl, DOC, DIC and conductivity
11
Daily
Since 1975 for some
Meteorological Station

T° min and max, radiations totales, total radiations, Ground T° to -50 cm and – 100 cm,

Air moisture min, max and average

1 station + 2 near observatory
Continuous
 
Since 1962
 
Soil moisture
Volumetric moisture of the soil at various depths, 3 measurement sites
3 profiles (from 5 to 155 cm)
Continuous
Since1988 for 1 site, 2006 for 2 other sites
Ground cover Chart
Map of the ground cover
Avenelles sub-catchment
Annual
Since1998
Charts
Pedologic and geologic charts, DTM 50 m, GIS supports …
 
 
  • Limnimetric stations

    All ORACLE limnimetric stations (11 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 11 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 19 precipitation gages with rocking troughs, all equipped with a recording system and remote-transmitter DANAE/RTC (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 Irstea. 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 (Orpheus Mini and Madofil probes). Measurements are carried out weekly with contact gauge for one station (Mélarchez piezometer).
    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 Cemagref site (Boissy-le-Châtel) at 4°C before being conveyed to the Chemistry laboratory (Cemagref –Antony) which follows a quality step and guarantees measurements reliability.
    All samples are analyzed by continuous flow automated spectrophotometry (Traacs800 Brann + Luebbe) for NH4, NO3, NO2, PO4 and chlorides concentrations. Dissolved organic and inorganic carbon are also analyzed using a TOC analyzer (Model 700 of BIORITECH) with a precision of ± 0,05 mg/l.Conductivity is measured directly using a conductimeter (WTW LF 538). Currently, in situ continuous measurements of nitrate concentrations and turbidity are carried out, via spectrophotometric probes (SCAN probes) in validation course.
    De 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 Irstea since 1962, and two stations managed by Meteo-France are located on the Observatory or in close vicinity.
    Part of Irstea 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). Soil moisture measurements of the surface (0-5 cm of depth) are acquired by “Theta” probes 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.