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Stormwater quality in an urbanising watershed in Perth

Newman, P.W.G. and Bishaw, T.D. (1983) Stormwater quality in an urbanising watershed in Perth. In: Proceedings of Water Quality Seminar, 13 - 14 October, Perth, Western Australia pp. 136-142.

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Stormwater in an urban area can be a significant contributor to deteriorating surface and ground-water quality though studies on it are rare. An instrumented flume in a stormwater drain at Ballajura enabled a study to be conducted in 1980 of stormwater quality in a newly developing Perth suburb. The results show that the pollutant load in the catchment could be attributed to the impervious surface and around 2/3 of the area under construction. The maximum concentration of pollutant occurs just before peak flow (especially nitrate) due to scouring. Over the 9 month period of the study nitrate was found to decrease over time suggesting it is being flushed from the catchment during this construction phase, whilst phosphate had a constant release pattern. Total phosphorus and total nitrogen follow the pattern of total suspended solids in the stormwater as most of the nutrients are in the organic matter in these solids. This suggests that most stormwater pollution comes from organic matter in soil deposited on impervious surfaces. However after the first flush most stormwater pollutants (especially ammonium) come from rainfall. Overall the stormwater is of marginally better quality than the receiving body of water. Very low phosphate concentrations are the major distinguishing characteristic of this Perth stormwater compared to others around the world and in Australia. This is consistent with the low phosphorus content in Bassendean sand and in plants (hence organic material) in this area. The importance of soil organic matter in stormwater has not been pinpointed before.

Publication Type: Conference Paper
Murdoch Affiliation: School of Environmental Science
Publisher: Water Research Foundation of Western Australia
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