Flood interpretation in case of measurement failure. The Wamme River in 2021.

During the extreme flood events that occurred in Belgium in July 2021, several measuring devices failed before the flow peak. This was the case at Hargimont on the Wamme River, where it appeared difficult to interpret the event a posteriori and to reconstruct reliable time series of water levels and discharges. However, such interpretations are essential to help decisionmakers to mitigate similar risks in the future. Most of the time, the measurement failure is clearly visible, and misinterpretation can be easily avoided. However, in some other cases, such as here, measurements seem to be recorded normally, whereas it was not the case because of clogging of a gauge, or displacements of the device. Using a combination of hydrological and hydraulic modelling, it was possible to highlight the erroneous measurement and to propose a corrected hydrograph.