The measuring of the volume of water discharged into the receiving water is of increasing interest to the operators and is, in some cases, already prescribed by law, especially at discharge thresholds.
The big problem in measuring such amounts of water is the accuracy of the measurement and thus the reliability of the recorded data. Particularly at the beginning and end of a discharge, large quantities of water may not be recorded. In most cases, this is due to the fact that the water volumes are discharged via a concrete sill whose geometry is not clearly defined for inclusion in the water volume calculation. The decisive influencing factors here are a non-horizontal design of the sleeper, an unsteady geometry seen over the length of the sleeper and undefined surface roughness.
The factors listed here reflect the prevailing condition at the basin and control overflows in operation. Under these circumstances, even a highly accurate measuring technique for measuring the overfall height is not able to compensate for the errors regarding the assumed overfall coefficient that enter into the calculation.
The decisive optimisation of the accuracy of a spill quantity measurement therefore lies in the production of a defined spill crown with a known spill coefficient.
In order to further improve the results, it is advisable to include other influencing factors such as baffles located upstream or the direction of the inflow after installing an Aqua-Mes spillway and to take these into account when drawing up the Q-h line.
If an imperfect overflow can occur, e.g. due to underwater accumulation, this underwater level must be recorded by means of a separate measuring probe and integrated into the calculation of the overflow water quantity via a corresponding coefficient.