10.4122/1.1000001276 Sharpe, A. Clifforde, I.T. Martin, P. Modelling tidal effects in catchments with large variable tidal infiltration DTU Library, Technical University of Denmark (DTU) 2005 Storm Overflow Tidal Infiltration Sewer Network Model Infiltration Survey Black and Veatch en Conference full text 10.4122/1.1000001275 application/pdf 1 This paper describes a project to find a cost effective way of reducing storm overflow spill frequency to an acceptable level on a combined sewer system experiencing excessive tidal infiltration. Tidal infiltration reduction works had already been carried out, but infiltration remained high. Normally, where variable tidal infiltration is present but does not comprise a significant fraction of the flow in the sewer, an allowance can be made assuming a constant inflow equal to the peak observed tidal inflow. In this particular study, however, the tidal component was so large that this approach would be excessively conservative. Although large rainfall events and high tide conditions can coincide, they don\342\200\231t always. A sewer network model utilising continuous simulation was used to fully understand the impact of this tidal infiltration and then to size appropriate spill reduction measures. The paper describes how extensive tidal inflow surveys were used to develop a synthetic long term tidal inflow hydrograph taking into account variations in tide height throughout each month. This was used in conjunction with a long term rainfall time series to assess present and proposed systems spill frequencies, enabling a credible assessment of proposed storm storage provision to meet the spill frequency requirements.