A method for the evaluation of pollution loads from urban areas at river basin scale

Abstract

The European water framework directive (WFD) requires the identification of significant human pressures and impacts on water bodies. This is part of the wider analysis of river basins required by Article 5 (and Annex II) of the WFD, which must be completed by the end of 2004. The human pressures on surface waters include point and diffuse source pollutions, water abstraction, water flow regulation, morphological alterations and land use patterns. In order to be able to complete the analysis of significant pressures and impacts before the WFD deadline it is necessary to maximise the use of existing information. A method using only existing information for the evaluation of point source pollution at river basin scale, especially the pollution loads from drained urban areas into surface waters was therefore proposed. This method includes an approach to estimate imperviousness in urban areas and to calculate sewer overflow volume at river basin scale. The imperviousness in urban areas is estimated using information on land use in CORINE Landcover or ATKIS (Official Topographic–Cartographic Information System). Data used for the evaluation of sewer overflows, such as rainfall depth, sewer lengths, dry weather flow volume and total volume of combined wastewater discharged to wastewater treatment plants, are available from German Weather Survey, or they are, like in North Rhine-Westphalia, stored in databases. Imperviousness in the Wupper basin and nutrient inputs from urban areas into the Wupper river system were calculated in a case study and compared with the results of other investigations.