Southern Water (and its predecessors), along with all other Sewerage Undertakers, have endorsed the guidelines laid down in Sewers for Adoption
since its introduction in 1980. The current issue of Sewers for Adoption
, as with previous editions, identifies hydraulic design requirements for both foul and surface water systems. With regard to surface water systems, Sewers for Adoption states that “The system should be designed not to flood any part of the site in a 1 in 30 year return period design storm unless a different standard is used by the Undertaker”
. Southern Water designs new and upgraded surface water systems to a 1 in 30 year design. The company has in the past, and in the future will continue to, request that developers design surface water systems to the 1 in 30 year design standard. Environment Agency guidelines state that storage below ground should not exceed the 1 in 30 year design. All additional storage up to the 1 in 100 year should be provided for above ground.
Southern Water agrees that the concept that run-off from development sites should mimic the site before it was developed is sound but it must be recognised that much of the area being drained after development takes place is of land drainage origin. Sewerage Undertakers do not have a responsibility for this element and therefore it is appropriate to design systems that can deal with piped flows as well as overland flows. Above ground attenuation meets the objectives of both the Environment Agency, Sewerage Undertakers and land owners in an environmentally sympathetic way and at an economic cost.
Southern Water is supportive of the concept underpinning Sustainable Drainage Systems (SuDS). However, it is felt that it is inappropriate for all sites and that the technical thinking needs to be developed further before it can be considered for general introduction. Southern Water does not adopt SUDS systems.
Land drainage and groundwater will not be allowed to discharge into the public sewerage systems either directly or via private drains or sewers.