French vertical flow constructed wetlands: reed bed behaviour and limits due to hydraulic overloading on first stage filters

Study of the hydraulic limits of reed beds, based on the knowledge of hydrodynamics in unsaturated porous media, shows the ability of the system to accept flow overloads. Measuring different parameters (flow, pollutant removal, infiltration rate (IR), pressure head profiles) in pilot and full?scale studies, we suggest new hydraulic limits with accompanying sizing rules and operational recommendations according to the level of deposit on the filter surface. Overloads of ten times the dry weather flow are possible whilst still complying with the European standards.