Most cities sweep streets to maintain appearance and to keep storm grates open, not to improve water quality. But research shows that sweeping more than twice a year, the typical schedule for many public works departments, does, in fact, lower the amount of nutrients in stormwater runoff.

Trees provide many ecological and social benefits, but leaves, seeds, and pollen contain two nutrients targeted by stormwater regulators. Phosphorus (P) limits the growth of algae in freshwater; nitrogen (N) is often a limiting, or co-limiting, nutrient in estuaries.

Until fairly recently, the role of vegetative debris vis-à-vis stormwater compliance goals wasn’t well understood. However, two studies have shed light on how sweeping mitigates the urban canopy’s environmental impact. We used those results to develop an open-source, free Excel-based tool that any public works department can use to develop and justify a cost-effective sweeping schedule.

Next page: Planning for enhanced sweeping