Hydrologic data of the Strengbach catchment

Hydrological monitoring began in September 1986. An H-flume (1.45m wide x 3.03m long x 0.76m high) is installed at the Strengbach catchment outlet. Automatic water level measurements are performed in a stilling well hydraulically connected to the flume and located in a frost-free shelter.
The water level is measured at a variable time step between 2 minutes (high-flow events) and 1 hour using an Alcyr data logger connected to an immersed ultrasonic probe. Installed in August 1988, the sensor has never been replaced. The Alcyr data logger has changed over time. Initially, the recorder was a SAB-600LMU model. In 2003, it was a CYRUS model. It was replaced at the end of July 2011 by a CYR2/US V23 model.
Every two weeks, the water level measurement is checked by direct reading on a limnimetric scale installed in the flume. The difference between the height read and the height measured has never exceeded 2mm in low water conditions and 1.4cm in rare very high-flow periods.
The water level data are checked and corrected if necessary: outliers are removed, data are corrected for stilling well maintenance, wood jams or non-physical flood recession and data are smoothed for very high-flow periods. To help validate the data, the paper recordings of the water level obtained using an OTT limnigraph, as well as the meteorological data of the site, are consulted. The validated data is provided at a variable time step between 2 minutes and 1 hour. If too many consecutive invalid data have been identified and outside of rainy periods, the data can be estimated (affine approximation between 2 successive valid values).
The discharge was calculated using the validated water level data and the rating curve of the flume. This curve is occasionally checked by gauging, mainly during low-water periods. No derating has ever been observed.
At the end of November 2016, a private pond (522m²) was created upstream of the outlet, in direct connection with the Strengbach stream. The pond is partly fed by water from the stream and this water is returned to the stream after a stay in the pond. The water intake and discharge systems are cleaned regularly, which occasionally leads to significant disturbances in the hydrological dynamics of the stream (reversed peaks and peaks outside of rain or snowmelt periods). At the beginning of June 2022, a change to the pond's drainage system reduced the number of disturbances, but did not completely eliminate them. In the absence of any satisfactory means of correction, these disturbances of the stream's hydrological regime have not been removed from the data. Historical background. These data have been acquired since 1986, thanks to the involvement of many people - technicians, engineers and researchers - who have worked to ensure the continuity and quality of the measurements, both in the field and in the laboratory. We cannot name them all here. The Observatory was initiated by research projects conceived and led by Bruno Ambroise, Bertrand Fritz and then Anne Probst.A brief summary of the history of work on the Strengbach watershed is available on the website: https://ohge.unistra.fr/lobservatoire/historique.