Department of Civil Engineering
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Item Investigation of urban water quality using artificial rainfall(Water Environment Federation, 2004) Goonetilleke, AshanthaAs the concept of sustainable communities is gaining increasing recognition around the world it is of critical importance to investigate the water quality of urban environments. The contamination of waterways in urban communities seriously affects the utility of water for different purposes and degrades the aesthetic value of natural watercourses. Research investigations in the past have generally focused on suspended solids and nutrients, which are relatively easy to monitor. Unfortunately the build-up and wash-off of micro pollutants such as polycyclic aromatic hydrocarbons (PAH) and heavy metals (HM) have received limited research interest in urban water quality research even though these can cause significant health and environmental impacts even at low concentrations. This paper describes how artificial rainfall, using a specially designed highly portable rainfall simulator was employed in order to generate water quality data from urban environments. This approach was adopted in order to investigate the wash-off of pollutants from paved surfaces and to overcome constraints due to the highly unreliable rainfall in South-East Queensland Australia. The rainfall simulator was able to demonstrate its ability to satisfactory simulate natural rainfall in the area. The results obtained confirmed that the rainfall simulator is a reliable tool for urban water quality research and can be used to simulate pollutant wash-off.Item Understanding the role of land use in urban stormwater quality management(Elsevier, 2005-01) Goonetilleke, AshanthaUrbanisation significantly impacts water environments with increased runoff and the degradation of water quality. The management of quantity impacts are straight forward, but quality impacts are far more complex. Current approaches to safeguard water quality are largely ineffective and guided by entrenched misconceptions with a primary focus on ‘end-of-pipe’ solutions. The outcomes of a research study presented in the paper, which investigated relationships between water quality and six different land uses offer practical guidance in the planning of future urban developments. In terms of safeguarding water quality, high-density residential development which results in a relatively smaller footprint would be the preferred option. The research study outcomes bring into question a number of fundamental concepts and misconceptions routinely accepted in stormwater quality management. The research findings confirmed the need to move beyond customary structural measures and identified the key role that urban planning can play in safeguarding urban water environments.Item Analysis of heavy metals in road-deposited sediments(Elsevier, 2006-07) Goonetilleke, AshanthaRoad-deposited sediments were analysed for heavy metal concentrations at three different landuses (residential, industrial, commercial) in Queensland State, Australia. The sediments were collected using a domestic vacuum cleaner which was proven to be highly efficient in collecting sub-micron particles. Five particle sizes were analysed separately for eight heavy metal elements (Zn, Fe, Pb, Cd, Cu, Cr, Al and Mn). At all sites, the maximum concentration of the heavy metals occurred in the 0.45–75 μm particle size range, which conventional street cleaning services do not remove efficiently. Multicriteria decision making methods (MCDM), PROMETHEE and GAIA, were employed in the data analysis. PROMETHEE, a non-parametric ranking analysis procedure, was used to rank the metal contents of the sediments sampled at each site. The most polluted site and particle size range were the industrial site and the 0.45–75 μm range, respectively. Although the industrial site displayed the highest metal concentrations, the highest heavy metal loading coincided with the highest sediment load, which occurred at the commercial site. GAIA, a special form of principal component analysis, was applied to determine correlations between the heavy metals and particle size ranges and also to assess possible correlation with total organic carbon (TOC). The GAIA-planes revealed that irrespective of the site, most of the heavy metals are adsorbed to sediments below 150 μm. A weak correlation was found between Zn, Mn and TOC at the commercial site. This could lead to higher bioavailability of these metals through complexation reactions with the organic species in the sediments.Item Mathematical interpretation of pollutant wash-off from urban road surfaces using simulated rainfall(Elsevier, 2007-07) Goonetilleke, AshanthaIn the context of stormwater quality modelling, an in-depth understanding of underlying physical processes and the availability of reliable and accurate mathematical equations, which can replicate pollutant processes are essential. Stormwater pollutants undergo three primary processes, namely, build-up, wash-off and transport, before accumulating into receiving waters. These processes are expressed mathematically by equations in stormwater quality models. Among the three processes, wash-off is the least investigated. This paper presents the outcomes of an in-depth investigation of pollutant wash-off processes on typical urban road surfaces. The study results showed that a storm event has the capacity to wash-off only a fraction of pollutants available and this fraction varies primarily with rainfall intensity, kinetic energy of rainfall and characteristics of the pollutants. These outcomes suggest that the exponential equation commonly used for mathematically defining pollutant wash-off would need to be modified in order to incorporate the wash-off capacity of rainfall. Consequently, the introduction of an additional term referred to as the ‘capacity factor’ CF is recommended. CF primarily varies with rainfall intensity. However, for simplicity three rainfall intensity ranges were identified where the variation of CF can be defined. For rainfall intensities less than 40 mm/h, CF varies linearly from 0 to 0.5. For rainfall intensities from 40 to around 90 mm/h, CF is a constant around 0.5. Beyond 90 mm/h, CF varies between 0.5 and 1.Item Understanding road surface pollutant wash-off and underlying physical processes using simulated rainfall(IWA Publishing, 2008-04) Goonetilleke, AshanthaPollutant wash-off is one of the key pollutant processes that detailed knowledge is required in order to develop successful treatment design strategies for urban stormwater. Unfortunately, current knowledge relating to pollutant wash-off is limited. This paper presents the outcomes of a detailed investigation into pollutant wash-off on residential road surfaces. The investigations consisted of research methodologies formulated to overcome the physical constraints due to the heterogeneity of urban paved surfaces and the dependency on naturally occurring rainfall. This entailed the use of small road surface plots and artificially simulated rainfall. Road surfaces were selected due to its critical importance as an urban stormwater pollutant source. The study results showed that the influence of initially available pollutants on the wash-off process was limited. Furthermore, pollutant wash-off from road surfaces can be replicated using an exponential equation. However, the typical version of the exponential wash-off equation needs to be modified by introducing a non dimensional factor referred to as ‘capacity factor' CF. Three rainfall intensity ranges were identified where the variation of CF can be defined. Furthermore, it was found that particulate density rather than size is the critical parameter that influences the process of pollutant wash-off.