ABSTRACT
SURF ACE water sewers provide the means for collection and discharge of natural precipitation, i.e. rainfall, snow, etc. They may either form a part of a 'combined' sewerage system to carry foul domestic wastes in addition to the surface water or they may be 'separate'. In the latter case, a further completely independent system of sewers is provided to deal with the foul sewage. Surface water sewers are usually designed to discharge to the nearest convenient watercourse when they are part of a 'separate' system. If they form part of a 'combined' sewerage system, they will normally discharge to a sewage treatment works; in this case storm sewage overflows may then be provided at suitable points along the sewers so that excess flows can be diverted to neighbouring watercourses in times of storm. As these overflows can be sources of pollution in a stream, the present tendency is towards 'separate' rather than 'combined' sewers, but many existing systems are either combined or at best only partially separate.
