Impact on runoff quality by the concrete drainage system

A major source of pollution of urban waterways is from urban runoff. Research over the past 20 years has lead to a greater understanding of the source and how to control many pollutants. However, recent investigations by the authors has identified that concrete, being the dominant material for public drainage systems including gutters and pipes, has a significant impact on the chemistry of urban water runoff. This in turn is influencing the water quality within urban creeks. Across the Northern suburbs of Sydney, reference or undisturbed natural creeks are acidic and characterised by their low alkalinity and electrical conductivity. Urban creeks, located with similar geology and soil, are mildly acidic to mildly alkaline with much higher alkalinity and electrical conductivity. To ascertain what may be a causal factor for this difference in water chemistry, rainwater collected within the catchment was pumped through various concrete pipes and along gutters. The results identify that the dissolution of cement products changes a range of analytes particularly calcium, bicarbonate, potassium and pH. There are significant changes to urban water quality as a result of the intransport processes associated with the concrete drainage system. This should be factored into the design of urban drainage schemes particularly if they discharge into naturally acidic or minerally poor waterways.