A GIS-based screening tool is described for identifying and ranking sensitive receiving environments (SREs) at risk from road runoff from state highways and local roads in New Zealand. The tool focuses on the particulate fraction of runoff and the risk this poses to ‘depositional’ receiving environments.
The tool uses the source-pathway-receptor concept and is applied on a catchment basis. Source strength is expressed either in vehicle kilometres travelled (VKT) or relative pollutant load. Pathways are assigned an attenuation factor in terms of ‘connectivity’ to the receiving environment. Receiving environment sensitivity is based on depositional characteristics of the waterbody type, with secondary attributes covering ecological and human use values.
Tier 1 identifies SREs potentially at risk using VKT per sub-catchment. Tier 2 further assesses risk using a model to estimate vehicle contaminant load (particulate matter, zinc and copper) for comparing road networks. Risk factors are combined to give an overall measure of relative pollution risk for ranking road networks on a comparative basis. The paper outlines the method and findings from a pilot study in the Porirua area of Wellington. The tool is intended to assist roading authorities in prioritising areas that could benefit from installation/upgrade of treatment systems for road runoff.