SEWAGE DISPERSION IN AN ESTUARY WITH DISTINCT EBB AND FLOOD CHANNELS

As a result of a combination of the European Communities (EC) Bathing Water and Urban Waste Water Treatment Directives, the option of discha rging biologically treated effluent into estuaries and shallow coastea l waters through short outfalls is being increasingly considered. This has meant that sewage disposal models are now required to resolve wat er movements in inshore waters. As part of an environmental assessment into the options for the treatment and disposal of sewage from Felixs towe, Harwich and Dovercourt, Anglian Water commissioned WRc to produc e a bacterial dispersion model of the area, It was necessary to quanti fy the complex flows suspected in Harwich Harbour and to be able to si mulate their impact on effluent dispersion, This paper describes the d evelopment and application of this model. A detailed 2D hydrodynamic m odel was calibrated against Vessel Mounted Acoustic Doppler Current Pr ofiler data gathered in the area. A bacterial dispersion model driven by this hydrodynamic model was validated using bacteriophage tracer re leases. The model has been applied to demonstrate that the treatment o ptions under consideration will comply fully with the Bathing Water Di rective and are constant with the Anglian Water Environmental Policy.