Assessment of the overflow discharge in complex CSO chambers with water level measurements – On-site validation of a CFD-based methodology

• A real-site validation of a methodology to assess overflow discharges is proposed.
• This assessment is only using non-intrusive water level measurements.
• The methodology is based on computational fluid dynamics models.
• It integrates a data-validation methodology identifying a possible sensor drift.

Combined sewer overflows (CSO) often present complex geometries and variable hydraulic conditions that do not fit any standards and make it tough to measure their discharge. A CFD-based methodology to assess the overflow discharge and the related uncertainties using measurements of the water depth in sewage networks, and especially in non-standard CSOs, has therefore been developed. This methodology presents several advantages: it includes the optimization of the sensor location, integrates the boundary conditions variability and calculates the global uncertainty related to the chosen height-discharge relationship. Moreover, the final instrumentation requires little maintenance and can be secured.This particular study focuses on a one-site validation of this methodology through the example of “Herbet” CSO, one of the biggest of Clermont-Ferrand's sewer network, FRANCE (up to 4 m3/s). This article also aims learning by feedback from the on-site measurements and defining a method to validate the acquired data. It is particularly interesting to secure the measurement and detect a possible drift in a sensor in real-time.