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This short video and this field procedure present the essentials of INRAE streamgauging rulers. Measurements can be entered and processed using this spreadsheet. The CATER Calvados Orne Manche association also offers user documentation and a smartphone gauging application (Qràj).

Introduced by Fonstad et al. (2005) and modified by Pike et al. (2016), the streamgauging ruler (a.k.a. transparent velocity-head rod) is an inexpensive, easy and quick to use streamgauging tool, providing reliable discharge measurements under the right application conditions (velocity greater than 20 cm/s over most of the cross-section, operator stable within the flow). The principle is simple: the water level difference between upstream and downstream faces of a board blocking the flow increases with the velocity-head related to the depth-average flow velocity. Using a semi-empirical calibration, the velocity can be calculated from the water level difference. So, discharge can be measured like with a conventional current meter on a wading rod, and more quickly. This calibration was validated up to 120 cm/s approximately.

The model developed by INRAE in 2020 (Le Coz et al., 2021) is a little more expensive (commercially available for about €200) but it is still relatively easy to build and significantly improves ergonomics and measurement. Comparison experiments with reference measurements performed in a hydraulic laboratory and at different field sites (Pernot, 2018) confirmed the semi-empirical calibration relationship established by Pike et al. (2016), and discharge measurements are generally within 10% of the reference discharge (Le Coz et al., 2024). However, operator effect related to the handling of the rulers and the reading of the water level difference can lead to larger deviations, which requires training and attention at this stage of the measurement process.

 See the geographical distribution map of INRAE streamgauging rulers around the world:

As the method is extremely simple and quick to apply, it is well suited for rapid discharge estimates, training or demonstration, citizen science programmes or cooperation with services with limited resources and/or not specialised in hydrometry. We distribute the instrument, a procedure and a spreadsheet for calculating velocities and discharge. We help the deployment of the technique by different operators (scientists, environmental agencies, river boards, irrigation boards, agricultural agencies, French Federation of Speleology…).

Do not hesitate to contact us if you are interested! (contacts: Jérôme Le Coz, Mickaël Lagouy).

Acknowledgment

The development of the INRAE streamgauging ruler was supported by the French Biodiversity Agency (OFB).

References

Fonstad, M., Reichling, J., Van de Grift, J., 2005. The transparent velocity-head rod for inexpensive and accurate measurement of stream velocities. Journal of Geoscience Education, 53(1):44–52.

Le Coz, J., Lagouy, M., Pernot, F., Buffet, A., Berni, C. (2021). Jaugeages à bas coût par perches transparentes, SHF,  Colloque Hydrométrie 2021, Montpellier, 23-24 novembre 2021.

Le Coz, J., Lagouy, M., Pernot, F., Buffet, A., Berni, C. (submitted). The streamgauging ruler: a low-cost, low-tech, alternative discharge measurement technique. Journal of Hydrology (submitted, 2024)

Pernot, F., 2018. Elaboration de systèmes de jaugeage à bas coût, Mémoire de stage de fin d’étude. Irstea / Polytech Nice-Sophia, 48 p.

Pike, R., Redding, T., Schwarz, C., 2016. Development and testing of a modified transparent velocity-head rod for stream discharge measurements. Canadian Water Resources Journal, 41(3):372–384.