Case study — uncertainty inherent in metals build-up and wash-off processes

Abstract

This chapter presents the outcomes from a case study which investigated how uncertainty inherent in build-up and wash-off of metals commonly present in urban catchments, could influence stormwater quality. The investigation found consistent and significantly high concentrations of Al, Cr, Mn, Fe, Ni, Cu, Zn, Cd and Pb in the particle size fraction <150 µm than in the particle size fraction >150 µm. When considering consecutive events of build-up and wash-off, the temporal variations in the build-up loads of metals associated with particle size fractions <150 and >150 µm were not consistent with their wash-off loads. These inconsistencies could be potentially due to the interactions between metals and particles that are determined by the particle physico-chemical characteristics. While particle behaviour was found to drive the variability in metal build-up and wash-off, the need for characterising process variability in stormwater quality modelling was highlighted, enabling the quantitative assessment of process uncertainty associated with stormwater quality predictions.