Integrated approach to the point-non point-pollution abatement in urban drainage

Abstract

An area in Switzerland of 260 km2 with 230 000 inhabitants was analysed for the feasibility of combined sewage overflow (CSO) tanks to reduce the pollution in receiving waters during rain events. The case study demonstrates the consideration of the point and of the non point pollution with respect to choice and application of water pollution control measures in urban drainage. For example, measures which reduce pollutant sources (e.g. substitution of phosphorus in detergents) or reduce surface runoff (e.g. dispersed retention or infiltration of rainfall runoff) are more efficient than a strategy of uniform and area wide application of CSO tanks. The new Swiss guideline for Integrated Urban Drainage Master Planning (IUDMP) introduces a radical changes in the scope and in the procedures of planning process. This guideline defines the urban drainage system as one single system, consististing of urban area, soil and ground water system, drainage network, waste water treatment plant and receiving waters. The consideration of comprehensive urban drainage system allows the choice of site-specific and problem-related measures.