A study on the benefits of street sweeping for reducing stormwater contaminant loads to streams has been completed for Nelson City Council (NCC). The study found that properly designed street-sweeping programmes can reduce contaminant loads in catchments by approximately 30 per cent.
A key parameter in successful sweeping is local climate. Street sweeping is more effective in areas with longer intervals between storms (which compete with street sweeping). The best contaminant removal is achieved by sweeping one to two times between rainfalls. Therefore, the longer the period between storms, the lower the sweeping frequency required for best contaminant removal. This also makes it the most cost-effective.
NCC is considering options for implementing targeted and cost-effective sweeping and is especially keen to identify 'hot spots', for example around light industrial areas, that contribute a disproportionately large amount of contaminants via road runoff. A concentrated effort on these subcatchments will have the greatest value for money.
NIWA Contact: Dr Craig Depree [email protected]
