Could porous pavements be part of the urban water solution?

As water use in Australia is fast approaching, and in some cases, exceeding the limits of sustainability, urban stormwater management is therefore a high priority at the national, state and local government levels. One of the greatest challenges lies in achieving the required level of stormwater treatment within established, densely populated urban areas (such as inner city areas). Most of the available stormwater management measures are difficult or impossible to implement on a wide scale within developed urban areas due to infrastructure, space and/or cost constraints; with porous pavements being one technique, which can be deployed in a wide range of space-constrained situations. Despite being a promising stormwater management technology that is widely used abroad, Australia is lagging behind in the development and application of porous pavement, mainly due to a low level of confidence in its treatment performance under Australian conditions, and early perceptions relating to clogging. The present thesis has examined the hydraulic and pollutant removal capabilities of three types of commonly available porous pavement systems; monolithic Porous asphalt, modular Hydrapave, and monolithic Permapave. Compressed time-scale laboratory experiments were used to better understand their long-term behaviour and, their ability to effectively reduce suspended solids and particulate bound pollutants under drying and various wetting conditions. All three types of porous pavement systems were able to effectively reduce concentrations of suspended solids but nutrient removal was more variable. Interesting observations and associations were made about the behaviour of nutrients, particularly nitrogen during high (short contact time) and low (long contact time) flows. Unlike the behaviour of TP outflow concentration which increased gradually from low to high flows, the average TN outflow concentration gradually decreased from low to high flow, suggesting that low flows (longer detention time) facilitates the breakdown of trapped sediment in the clogged layer. The observed TN behaviour is contrary to the principle of the MUSIC (Model for Urban Stormwater Improvement Conceptualization) software that pollutant removal performance increases with a longer detention time. This thesis has also examined in detail, the physical clogging process in porous pavement systems. A simple black-box regression model that predicts physical clogging was developed as a function of cumulative volume and Brisbane climatic conditions. Another significant finding from the present study was the influence of variable wetting and drying regimes on the rate of clogging. Systems that received variable flow magnitudes, along with long drought conditions were found to have doubled the lifespan of systems receiving low flow magnitudes with the absence of drought. A number of knowledge gaps remain. However, this research has provided valuable insights into the evolution of clogging and a comprehensive overview of the long-term performance of porous pavement systems. A simple clogging model was also developed that helps inform designers and asset managers on the average life expectancy of porous pavement systems under drying and various wetting conditions in Australia.