The 'storm tunnel' proposed by Thames Water beneath the River Thames (NCE 15/29 December) would be designed to intercept combined sewage flows from historical 'settlement catchments' along a logical route. Computer aided, it would ensure collection - without flooding - of the Ofwat required 30 year return storm runoff from all or any of the separate catchments.
From the tunnel's downstream end, the 'stored' combined sewage would be delivered to treatment. To avoid the full 30 year return storm runoff from the total catchment requiring treatment, Environment Agency discharge consent would allow spills to the Thames say once in five years.
Over a five year period, and starting at the downstream end, this would bring progressive benefit to the Thames and the catchments along the tunnel route. I can sense grudging approval from Sir Joseph Bazalgette!
Denis King (M), denfk@onetel. com