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CRC PUBLICATIONS |
A Review of Urban Stormwater Quality Processes
Hugh Duncan
Publication Type:
Technical Report
This is a publication of the initial CRC for Catchment Hydrology
CRC Program:
Urban Hydrology (Previous CRC)
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Publication Keywords:
Storm Sewage
Water Quality (Natural Waters)
Urban Areas
Runoff (Urban)
Pollution (Surface Water)
Stormwater Management
Contamination
Pollution Sources
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Abstract / Summary:
This document describes the physical processes which contribute to the contamination of urban stormwater runoff, and forms part of a broader review of the English language literature on urban stromwater quality research. The processes discussed are wet and dry deposition of contaminants from the atmosphere, interception on vegetation and artificial above-ground structures, buildup of contaminants on impervious surfaces, washoff from surfaces into formed channels or pipes, transport along channels and pipes, quality changes during storage, and the influence of receiving waters on the scale and detail of analysis.
Atmospheric deposition typically supplies as much nitrogen as is washed off in urban runoff, and a smaller proportion of suspended solids, phosphorus, COD, and heavy metals. The main pollutant sources accessed by interception processes are accumulated dry deposition on roofs and vegetation, and solution of roof and plant materials. Undiluted roof runoff may be highly toxic to fish. Buildup of material on impervious surfaces can be described as a dynamic equilibrium process between contributing and non-contributing areas. Surface load increases with antecedent dry period, but the shape of the curve cannot be determined with any accuracy.
Washoff appears to be the limiting process for urban stormwater pollution in most situations, and is associated most strongly with rainfall intensity. Although almost universally used in modelling, the exponential description of washoff is a poor measure of real physical processes. An alternative function based on rainfall intensity is proposed. First flush is by nature and definition a characteristic of small catchments.
Plant litter is a major source of organic matter and nutrients, but its contribution to receiving waters will not be fully recorded by convential water qualiaty measurements, The quality of urban storm runoff can be greatly improved by storage in ponds and wetlands. The main processes involved are settling of suspended material, averaging of dissolved material, and conversion of nitrogen between its chemical forms by bacteria. The size and nature of receiving waters help to define the optimum scale and detail or urban runoff quality analysis. Detail which is excessive, relative to the time and space scales of the ultimate objective, is not helpful in analysis and may be detrimental.
This report is not currently available for downloading. Printed copies can be purchased from the Centre Office.
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Centre Office:
CRC for Catchment Hydrology
Dept of Civil Engineering
Building 60
Monash University Vic 3800
Tel: +61 3 9905 2704
Fax: +61 3 9905 5033
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