Mesure de débit en rivière par station radar hauteur / vitesse selon la méthode de la vitesse témoin

International audienceIn recent years, stage / velocity radar stations have been installed in France. This type of stations provides measurements of water level and surface velocity at a fixed point of the cross‑section. Discharge is calculated as the product of the wetted area and cross‑sectional average velocity; respectively obtained using a stage‑area scale S(h) established from a bathymetry profile, and a relation between the index velocity measured by the radar (Vi) and the cross‑sectional average velocity (Vmean), established with gaugings. This is the «index velocity method ». As discussed through various examples, the index velocity method has advantages over traditional stage‑discharge rating curves: – Flood extrapolations are better known: velocity varies more slowly than water discharge with stage and the stage‑area relation can be predicted. – Managing bed evolution is easier because the Vmean(Vi) relation changes little and the S(h) relation is easy to reset with a bathymetry survey. – Monitoring the Vi(h) measured relation in real time allows detecting rating changes of the station. The wider use of the method and the development of measurement instruments will allow the future assessment of the uncertainty related to the calculation of water discharge. Perspectives for the bayesian analysis of index velocity ratings are discussed