A deposit trap is located upstream of the gauging station. Topographic surveys of this trap are performed regularly, if possible after each flood. The volume of sediment deposited between one survey and the next one is obtained by substraction of the topographic surveys. This volume of sediment can be attributed to the floods that occur between two surveys. The deposit trap is regularly cleaned to restore its storage capacity. If the deposit trap is already almost full when a flood occurs, it can be overflooded and it is not able to retain sediment anymore. In such case the volume of sediment obtained at the following topographic survey is underestimated, and is given a low quality code.