An event-based contaminant load model was developed to identify spatial patterns of stormwater total suspended solids (TSS) and heavy metal loads and assess potential reductions in contaminants loads by implementing various stormwater management options. The GIS-Excel based model estimates contaminant loads from an individual storm event based on different contributing impervious surfaces and key climate characteristics (rainfall intensity, duration, pH and antecedent dry days (ADD)). It then calculates the reduction in contaminant loads that could be achieved through source reduction (e.g. green roofs, repainting) as well as from treatment (e.g. raingardens (bioretention basins), wet ponds) applied to different surfaces within the catchment. The model was run for a case study catchment in Christchurch, New Zealand, to identify where ‘hotspots’ occurred for each contaminant. Model simulations of targeted management options were run, which predicted effective reduction of both TSS and heavy metals could be achieved with a strategy of combined source reduction and downstream treatment.