The North Tyneside bathing waters’ scheme reduces the frequency and quality of storm sewage which is discharged inshore from existing interceptor sewers along the coast.
Flow‐simulation modelling is applied to the existing system to determine the frequency and volume of interceptor sewer overflow against a range of storm intensity and return periods. The models are extended to an evaluation of new systems of storm‐sewage management.
An optimized solution is described in which new storm sewers are utilized for the storage of all storm‐sewage overflow discharges prior to screening and pumping of the storm sewage to sea via an outfall.
M r StaplesThe use of predictive modelling techniques, referred to rather briefly, requires further explanation. The relationship with the selection of priorities is best illustrated by a number of examples in which the modelling results cited principally relate to dissolved oxygen levels. Although this is not the only parameter modelled it is the one most easily interpreted.
58.The improvement in conditions in the River Thames is well known, but recent monitoring shows that 'success' is associated with a mean summer dissolved oxygen sag level to under 25% saturation in the third quarter of the year. It is understood that drought conditions in 1976 have led to flow being pumped back from the tidal river rather than the normal fresh water river flow over Teddington Weir, effectively achieving reuse of sewage effluent from the estuary. Contrary to first expectation, these conditions were associated with maintained and even improved conditions in the river quality, largely, it is suggested, because the events coincided with the commissioning of additional sewage treatment facilities. Prediction modelling by the University of Newcastle of dissolved oxygen levels suggests that for the River Tyne further treatment of the larger downstream discharge from Howdon may have advantage over extended treatment upstream, a reversal of the normal expectation expressed in the Paper. Nevertheless, the first priority of reducing gross visible pollutants properly overrides consideration of dissolved oxygen in implementing the Tyneside scheme, and demonstrates the need to balance objectives in according priorities.59. Similarly, the Mersey modelling by the Water Research Centre showed that long-term objectives can only be fully realized by adopting a high degree of treatment for effluents from the upstream catchment embracing the Manchester connurbation. Again, however, real and apparent progress in the lower estuary is more dependent on the interception and partial treatment of crude waste discharges from the lower estuary development.
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