EVOLUTION OF URBAN STORMWATER ENVIRONMENTAL ASSESSMENT METHODS: A CASE STUDY OF THE GREATER VANCOUVER REGION, BRITISH COLUMBIA

The Greater Vancouver Regional District and its member municipalities have recently completed an environmental monitoring and assessment program in support of its liquid waste management plan. Begun in 1993, the assessment program was designed to assist in determining management priorities for maintaining and upgrading sewerage and drainage infrastructure. The original methodology incorporated a discharge inventory, flow and quality estimation at selected sites, and an outfall-based receiving environment assessment program. Discharge characterization data allowed typical constituent concentrations to be determined for each discharge type. For stormwater, these concentration estimates were combined with hydrologic runoff analysis to calculate regional-scale urban runoff contaminant loads – both for the present and for future development scenarios. This loading information highlights that urban stormwater contaminant loads to some water bodies are expected to increase dramatically – in some cases more than doubling during a base growth forecast of forty years.It quickly became apparent that the outfall-based assessment component of the program would need to be modified for the examination of urban stormwater. A watershed-based assessment program, utilizing habitat and benthic community analysis, was later developed for stormwater discharges, and monitoring was conducted in nine small streams throughout the region. Rather than focus on an individual outfall, the program examined the cumulative effects of many upstream discharges. Results of the watershedbased assessment identified urban stormwater discharges to small streams to be one of the most significant environmental issues to be addressed in the region's long-term management plan.