The New York City Department of Environmental Protection (DEP) needed a watershed management strategy to address the risk of water quality degradation in the Croton watershed’s 12 reservoirs.

Malcolm Pirnie developed a risk-ranking methodology to address several water quality variables: pathogens, phosphorus, total suspended solids and toxics. The Pirnie team compared the risk of water-quality impairment among sub basins and helped prioritize which areas required management strategies.

The Pirnie team then developed a decision support tool to assess the impact of future management actions on pollutant generation and transport. A Geographic Information System (GIS) allowed the analysis to incorporate spatial data and provided a visual indication of the distribution of high-risk sub-basins across the watershed.

The risk-ranking methodology and the GIS provided tools to track ongoing activities within the watershed and objectively prioritize existing programs, as well as newly developed watershed management strategies.