Mathematical interpretation of pollutant wash-off from urban road surfaces using simulated rainfall

Abstract

In 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'C(F) is recommended. C(F) primarily varies with rainfall intensity. However, for simplicity three rainfall intensity ranges were identified where the variation of C(F) can be defined. For rainfall intensities less than 40 mm/h, C(F) varies linearly from 0 to 0.5. For rainfall intensities from 40 to around 90 mm/h, C(F) is a constant around 0.5. Beyond 90 mm/h, C(F) varies between 0.5 and 1.

Development and calibration of a rainfall simulator for hydrological studies

“…The use of RS in urban hydrology is relatively recent. Tucci et al (2000), Silva (2006) and Castro (2011), for example, used RS in experiments with permeable pavements, while Egodawatta (2007), Egodawatta et al (2007Egodawatta et al ( , 2009 and Miguntanna (2009) used an RS, developed by Herngren (2005), in researches on the accumulation and transport of pollutants in pavements and roofs, as well as in rainwater quality researches.…”

Index models to evaluate the potential metal pollution contribution from washoff of road-deposited sediment

“…Quantifying the relationship between RDS and washoff particles in urban runoff could provide a new method for estimating the pollution load that a waterway receives (Herngren et al, 2005;Zhao et al, 2011). A range of diffuse pollution models for urban areas have been proposed, including STORM, HSPF, DR3M-QUAL, SWMM, and SLAMM, and they have been used to estimate pollutant loads in runoff (Egodawatta et al, 2007;Wang et al, 2011). Despite the fact that the models mentioned above are widely used to estimate diffuse pollution sources in urban areas, they generally require substantial amounts of parameterization and calibration data (Shaw et al, 2006).…”

Understanding the relationship between heavy metals in road-deposited sediments and washoff particles in urban stormwater using simulated rainfall

“…Previous studies suggested that RDS and washoff particles had either an exponential, rating curve, or other relationship depending on a range of parameters such as surface characteristics, rainfall intensity and duration, RDS particle sizes, land use, etc. [7,9,[33][34][35][36][37]. However, it was unclear how particle size composition influenced the relationship of pollutants between RDS and washoff particles [38].…”

“…The rainfall simulation was designed according to Herngren et al (2005), Egodawatta et al (2007), and Xie et al (2008) [5,7,25]. The device consisted of two rainfall simulators.…”

“…Heavy metals washoff from RDS is an increasing problem associated with rapid urbanization that results in urban diffuse pollution [3,4]. Because of the difficulty associated with using natural rainfall events to investigate rigorous RDS washoff processes [5,6], washoff is the least understood among the three processes that occur before materials enter receiving waters (RDS buildup, washoff and transport) [7]. An in-depth understanding of these processes is essential to elucidation of the relationships of pollution between RDS and washoff particles [8,9].…”