Investigation of Stormwater Particles Generated from Common Urban Surfaces
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UNIVERSITY OF SOUTHERN QUEENSLAND Faculty of Engineering and Surveying Investigation of Stormwater Particles Generated From Common Urban Surfaces A Dissertation Submitted by Ian Malcolm Brodie For the Award of Doctor of Philosophy 2007 Principal Supervisor Dr Mark Porter Associate Supervisor Dr David Thorpe ABSTRACT Pollution due to urban stormwater runoff is a significant environmental issue. Large regional devices including sediment ponds and constructed wetlands are common features in the urban landscape to treat runoff. In keeping with this approach, data requirements to evaluate stormwater impacts have mainly been met by the monitoring of sizeable urban catchments, typically greater than 10ha in area. Urban runoff characteristics have thus been conventionally linked with broadly defined catchment attributes. Land use, as defined by zonings such as Residential, Commercial and Industrial, is an attribute often used to evaluate stormwater runoff from urban catchments. The emergence of Water Sensitive Urban Design (WSUD) in Australia is changing the management focus from the reliance on a small number of large-scale devices to many smaller-scale source controls distributed throughout the catchment. This paradigm shift in stormwater management places greater emphasis on small-scale processes within urban areas. Subsequently there is a need for more knowledge about stormwater generated from specific urban surfaces (roads, roofs, grassed areas etc). The objective of this study was to demonstrate how urban stormwater quality can be managed on the basis of urban surfaces. The study involved the collection of data for typical urban surfaces and the development of predictive models to estimate stormwater quality. A series of case studies is provided to illustrate the use of surface-related data and modelling tools in stormwater management, particularly in the context of WSUD. Non-Coarse Particles (NCP), defined as suspended solids less than 500μm in size, was selected as the stormwater pollutant under consideration. NCP is divided into the following particle size classes; Very Fine Particles (VFP, <8μm), Fine Particles (FP, 8-63μm) and Medium Particles (MP, 63-500μm). Laboratory methods to determine the concentration of these particle classes within stormwater runoff were adapted and refined from current standard methods. Organic content of each stormwater particle class was also determined. An innovative device, the flow splitter, was developed to collect runoff samples from urban surfaces. The flow splitter was designed to obtain a composite flow- proportional sample, necessary to derive the Event Mean Concentration of PAGE I stormwater particles. Hydraulic and sediment testing of a prototype flow splitter confirmed that the device is an accurate and unbiased sampling method. Flow splitters were installed at five monitoring sites within inner city Toowoomba, Australia. The sites have small catchments (50 to 450m2 area) representative of urban impervious areas (galvanized iron roof, concrete carpark and bitumen road pavement) and pervious areas (grassed and exposed bare soil). Overall, runoff from 40 storms with rainfalls from 2.5mm to 64.3mm was sampled during the period December 2004 to January 2006. A scatter plot analysis identified potential correlations between measured NCP loads and basic rainfall parameters such as rainfall depth and intensity. An exponential- type trend, consistent with many washoff models, is evident between load and average rainfall intensity for all surfaces. A composite index, referred to as the Rainfall Detachment Index (RDI), was found to be better than average rainfall intensity in explaining a relationship between NCP load and storm rainfall characteristics. The insight gained from the RDI led to the development of a particle Mass Balance Model for impervious surfaces. Depending on the surface type, the model was able for provide reasonable estimates (R2 = 0.74 to 0.97) against the measured NCP loads. Simpler analytical methods for particle load estimation were also developed in the study. A total of five methods were produced. An error analysis was conducted to compare the performance of each method to accurately reproduce the measured NCP loads. The analysis also included three methods used in current practice, which performed poorly compared to the new modelling techniques. The analytical methods provide useful tools in urban stormwater planning. The Mass Balance Model and measured surface-specific data were used in a number of case study examples to demonstrate possible applications. The applications included assessments of 1) the relative contribution that different urban surfaces make to the particle load in runoff; 2) how surface-specific data can be directly transferred to represent a large-scale urban catchment located in a different climate; 3) the particle loads generated from Residential and Commercial land uses; 4) the effect of exposed areas of bare soil on the particle loads from a Residential catchment; 5) the effect that widespread adoption of rainwater tanks may have on particle concentration in Residential urban runoff and 6) the particle load reductions by the use of a grass swale to treat road runoff. PAGE II CERTIFICATION OF DISSERTATION I certify that the ideas, experimental work, results, analyses and conclusions reported in this dissertation are entirely my own effort, except where otherwise acknowledged. I also certify that the work is original and has not been previously submitted for any other award, except where otherwise acknowledged. __________________________ ___________________ Signature of Candidate Date ENDORSEMENT ____________________________ ___________________ Signature of Principal Supervisor Date ____________________________ ___________________ Signature of Associate Supervisor Date PAGE III ACKNOWLEDGEMENTS This investigation involved a number of research activities including stormwater monitoring, laboratory analysis of samples and data modelling and analysis. Several people have made valuable contributions to these research activities during the course of the project. Firstly, the support and guidance provided by my supervisors, Dr Mark Porter and Dr David Thorpe, has been excellent and contributed to the success of the project. The research was financially supported by the Condamine Alliance and I am grateful to Penny Cook and Mark Schuster for this assistance. Members of the technical staff at USQ provided practical inputs to the project. Glen Bartkowski applied his considerable carpentry skills in fabricating the prototype sampling devices and associated testing rigs. Bernhard Black and Kim Larsen provided much appreciated support in the laboratory analysis of the stormwater samples. Chris Galligan built the five flow splitters that were used in the stormwater monitoring. Toowoomba City Council also had a signicant involvement in the project. Due to the concerted efforts of Sri Vigneswaran and Peter Lembo, the road sampling device was installed in a very timely fashion to sample a number of summer storms. Peter Keane provided rainfall and water quality data available from the Council monitoring system. Other organisations provided data to complement the research project. Don Neale from the Queensland Environmental Protection Agency provided historical air quality data for Toowoomba. Alastair McHaig and Lucy Peljo made available data from the Brisbane City Council stormwater monitoring network for my use. Finally, this dissertation would not have been completed without the care and support provided by my wife, Lyn, and my daughters, Ellen and Megan. PAGE IV ASSOCIATED PUBLICATIONS Brodie, I. and M. Porter (2004) Use of Passive Stormwater Samplers in Water Sensitive Urban Design. ‘WSUD2004 Cities as Catchments’ 2004 International Conference, Adelaide, Australia, 21-25 November 2004. Brodie, I. (2005) Stormwater Particles and Their Sampling Using Passive Devices. 10th International Conference on Urban Drainage, Copenhagen, Denmark, 21-26 August 2005. Brodie, I. (2005) Suspended Solids in Stormwater Runoff from Various Urban Surfaces. USQ Faculty of Engineering and Surveying Report to Condamine Alliance, September 2005. Porter, M., I. Brodie, M. Achmad and V. Aravinthan (2005) Researching Sustainable Future Urban Water Supplies. Engineers Australia Southern Engineering Conference 2005 ‘Managing Resources for a Sustainable Future’, Toowoomba, Australia, 15 October 2005. Brodie, I. (2005) Monitoring of Particle Washoff from Five Different Urban Surfaces. Presentation to 15th Queensland Water Symposium, Brisbane, Australia, 23-24 November 2005. Brodie, I. and M. Porter (2006) Stormwater Particle Characteristics of Five Different Urban Surfaces. 7th International Conference on Urban Drainage Modelling in conjunction with 4th International Conference on Water Sensitive Urban Design, Melbourne, Australia, 3-7 April 2006. Brodie, I. (2006) Prediction of Stormwater Particle Loads from Impervious Urban Surfaces Based on a Rainfall Detachment Index. 7th International Conference on Urban Drainage Modelling in conjunction with 4th International Conference on Water Sensitive Urban Design, Melbourne, Australia, 3-7 April 2006. Brodie, I. and M. Porter (2006) Error Analysis of Methods to Estimate Suspended Solids Loads in Urban Stormwater. Australian Journal of Water Resources (Accepted for publication). Brodie, I., Rosewell, C. (2007) Theoretical Relationships Between Rainfall Intensity and Kinetic Energy Variants Associated With Stormwater Particle Washoff. Journal