Urban water quality: stereotypical solutions may not always be the answer

Abstract

This paper discusses the outcomes of a research project which involved an in-depth investigation of pollutant wash-off by analysing the hydrological and water quality data from six areas having different land uses, in order to correlate urban form to water quality. The three main catchments selected were characterised by differing forms of land development and housing density; ranging from predominantly forested, to rural acreage-residential and forest to mixed urban development. Additionally, three smaller subcatchments within the urban catchment were identified for more detailed investigations into effects of increasing urban density on water quality. The data derived were initially analysed using univariate statistical methods to obtain an insight into the trends and patterns of variations in water quality. Subsequently multivariate ‘chemometric’ techniques were applied to identify linkages between various parameters and their correlation with land use. The outcomes from the study bring into question a number of fundamental concepts routinely accepted in stormwater quality management. A significant fraction of the pollution was in dissolved form, hence it is more bio-available and is therefore more likely to cause pollution in receiving waters. It could well be that this condition is linked to the climatic and rainfall conditions experienced in the study region. This would mean that the effectiveness of structural measures would not be universal and stereotypical solutions will not always prove adequate. These findings underline the need to move beyond the dependency on customary structural measures and end-of-pipe solutions and the key role that urban planning can play in safeguarding urban water environments. The univariate and multivariate statistical data analysis undertaken found that among the different urban forms, stormwater runoff from the area with detached housing in large suburban blocks exhibited the highest concentration and variability of pollutants. This was based on the concentration of various pollutants, their high variability and physico-chemical form. Rural residential on large blocks were only marginally better. It could be concluded that in terms of safeguarding water quality, high density residential development which results in a relatively smaller footprint should be the preferred option