Department of Civil Engineering
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Item Rainfall simulation as a tool for urban water quality research(Sage, 2005-05) Goonetilleke, AshanthaThis paper discusses the design of a rainfall simulator for undertaking urban water quality research. Currently there is limited understanding of many of the fundamental concepts relating to urban stormwater pollution. This can be primarily attributed to research studies being dependent on natural rainfall with its inherent high variability and the use of heterogenous urban areas. These factors can act as significant constraints to the transferability of research outcomes outside the study area. The proposed rainfall simulator has the potential to significantly enhance research outcomes, and has demonstrated its ability to successfully recreate the physical characteristics of natural rainfall. Rainfall simulation techniques used in agricultural research have been refined and made appropriate for use on paved surfaces. The procedures undertaken to calibrate its performance to match natural rainfall is described. It is important that the water used in the simulations is of a similar chemical quality to that of natural rainfall. This is because the chemical characteristics of rainfall can significantly influence the physicochemical characteristics of pollutants in runoff. A rainfall quality profile has been developed for the proposed study area using natural rainfall samples, and will form the basis for the chemical quality of the water used in simulations.Item Understanding heavy metal and suspended solids relationships in urban stormwater using simulated rainfall(Elsevier, 2005-07) Goonetilleke, AshanthaUrban stormwater from simulated rainfall on three different landuses in Queensland State, Australia (residential, industrial, commercial) was analysed for heavy metals and physico-chemical parameters such as Dissolved Organic Carbon (DOC) and Total Suspended Solids (TSS). Rainfall events were simulated using a specially designed rainfall simulator for paved surfaces. Event mean concentration samples were separated into five different particle sizes and analysed individually for eight metal elements (Zn, Fe, Cr, Cd, Cu, Al, Mn and Pb). Multivariate data analysis was carried out for the data thus generated. It was found that DOC and TSS influence the distribution of the metals in the different particle size classes. Zn was correlated with DOC at all three sites. Similarly, Pb, Fe and Al were correlated with TSS at all sites. The distribution of Cu was found to vary between the three sites, whilst Cd concentrations were too low to assess any relationships with other parameters. No correlation between Electrical Conductivity (EC), pH and heavy metals was found at the three sites. The identification of physico-chemical parameters influencing the distribution process kinetics of heavy metals in urban stormwater will significantly enhance the efficiency of urban stormwater management systems.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.Item Evaluation of pollutant build-up and wash-off from selected land uses at the Port of Brisbane, Australia(Elsevier, 2009-02) Goonetilleke, AshanthaThe quality of stormwater runoff from seaports can be an important source of pollution to the marine environment. Currently, little knowledge exists with regards to the pollutant generation capacity specific to seaports as they do not necessarily compare well with conventional urban land use. The research project focussed on the assessment of pollutant build-up and wash-off. The study was undertaken using rainfall simulation and small impervious plots for different port land uses with the results obtained compared to typical urban land uses. The study outcomes confirmed that the Port land uses exhibit comparatively lower pollutant concentrations. However, the pollutant characteristics varied across different land uses. Hence, the provision of stereotypical water quality improvement measures could be of limited value. Particle size <150 μm was predominant in suspended solids. Therefore, if suspended solids are targeted as the surrogate parameter for water quality improvement, this particle size range needs to be removed.Item Understanding the physical processes of pollutant build-up and wash-off on roof surfaces(Elsevier, 2009-03) Goonetilleke, AshanthaPollutants originating with roof runoff can have a significant impact on urban stormwater quality. This signifies the importance of understanding pollutant processes on roof surfaces. Additionally, knowledge of pollutant processes on roof surfaces is important as roofs are used as the primary catchment surface for domestic rainwater harvesting. In recent years, rainwater harvesting has become one of the primary sustainable water management techniques to counteract the growing demand for potable water. This paper presents the outcomes of an in-depth research study into particulate matter build-up and wash-off for roof surfaces. In this research, particulate matter was considered as the indicator pollutant where the processes related to other pollutants can be predicted based on the understanding generated for particulate matter. The study outcomes confirm that the build-up process on roof surfaces is comparatively similar to road surfaces. However, particle loads collected from roofs were significantly less compared to road surfaces and much finer in texture. Wash-off from roofs also showed significant similarities to wash-off from roads. A relatively high concentration of particulate matter was noted during the initial part of storm events. Furthermore, the amount of particulate matter remaining on the roof surfaces was significantly high for less intense rain events.