Dispersion process in conditions of real sewer systems – in situ experiments

A general assumption of most current models used to simulate flow in sewer systems (pipes) is that the sewers are considered as prismatic channels. However, in real conditions there are many factors, which affect the real flow. One of them is the occurrence of the sediments and deposits in sewer pipes, which significantly changes the flow conditions, as well as the dispersion process in sewer systems by creation of “dead zones”. Paper describes the effects of these zones on hydrodynamic dispersion process, which are particularly noticeable in hydraulic conditions of low flow rates in sewer system (sanitary, flow rates during dry period without rain …). In the study, there were applied two types of tracers and both used substances give identical results. Experimental results show that even though sewer pipes are considered as prismatic hydraulic channels, in the real conditions some irregularities resulted with dead zones creation are presented. Their influence on the mass concentration time-course shape is depending on the sediment layer thickness. Gaussian approximation of the one-dimensional advection dispersion equation for instantaneous pollution entry is not suitable for the sewer pipes with sediments occurrence. In case of sediments presence, the GEV and Gumbel’s approximation function looks to be more accurate.