Developing a rainfall contaminant relationship model for Christchurch urban catchments
Stormwater quality is receiving increased scrutiny in order to reduce ecological degradation of urban waterways. This involves its appropriate characterization and treatment before resource consents can be renewed or approved for surface water management. This study developed a rainfall-contaminant relationship (RCR) model to ascertain the degree of relationships from stormwater contaminant loads with antecedent dry period, time to peak rainfall intensity, magnitude of peak rainfall intensity, and total rainfall. Rainfall and key contaminant (TSS, Zn, Cu and Pb) data sets for a University carpark collected between 2007-2008 were used as input parameters for the model. A distinct contaminant first flush was observed within 30 minutes for each storm event while the relative metal abundance showed a pattern of Zn>Cu>Pb attributed to the high vehicle intensity use. The RCR model indicated a strong positive relationship between antecedent dry period and both Zn and Cu concentrations. Lead had a positive relationship with total rainfall. Results also showed that TSS concentrations were largely controlled by antecedent dry period and total rainfall but not by time to peak rainfall intensity. This model is being refined to provide end-users with a useful tool for estimating contaminant loads and their appropriate management in Christchurch urban catchments.