The Effect of the in-transport process on urban water chemistry: an examination of the contribution of concrete pipes and gutters on urban water quality

The objective of this study was to test the impact of concrete pipes on the chemistry of water and how this may be a factor that influences water quality in urban streams. While contemporary urban water management is increasing its understanding of the impacts of urban catchment development on the environment, little research has been undertaken on in-transport processes associated with the stormwater drainage network. Stormwater systems are designed primarily to manage the impacts of flooding and overland flow. Robust and hydraulically efficient materials, such as concrete pipes, have been the favoured to achieve these outcomes. An investigation of water quality in the northern suburbs of Sydney showed pH and bicarbonate levels were statistically higher in the developed catchments compared to the undeveloped or bushland catchments. This prompted the researchers to investigate if concrete, being the dominate material of the stormwater drainage system, may be contributing to this difference. Rainwater collected from the catchment was passed through various concrete pipes over a period of 120 minutes and measured for a range of analytes. The results reported that irrespective of the age of the concrete pipe there was a significant change in water chemistry when compared with the flows through a plastic stormwater pipe (used as a control). Newer pipes reported the greatest degree of change. The principal cause was the dissolution of cement products into the water. These findings are particularly relevant where the buffering of naturally acidic rain, primarily achieved through the dissolution of calcium from concrete drainage structures, alters the chemistry of natural water bodies. These ecosystems are naturally acidic and sensitive to changes in alkalinity and bicarbonate levels.