The Government of Ontario allocated substantial population growth to the nutrient-sensitive Nottawasaga River watershed. With that allocation, Nottawasaga Valley Conservation Authority (NVCA) needed to understand how to manage the new development in a way that either stabilized or reduced current loadings of phosphorus to protect water quality.

NVCA retained us to develop a standard and reproducible approach to estimate phosphorus loadings as a function of land use and to model the benefits of best management practice and low impact development to achieve targets of “no net increase” for new development.

We refined a previous export coefficient model for the Lake Simcoe watershed that we developed for the Ontario government to: 

• Reflect site-specific soil and runoff characteristics for the specific land use classes that are most often changed with urbanization, such as cropland, high intensity residential, industrial, commercial and transportation.
• Model export from unaltered land uses.
• Incorporate a variety of best management practices and low impact development practices to reduce phosphorus export from new development.
• Link all estimates into a site-specific phosphorous budget comparing loadings before and after development.

The tool was provided to NVCA in a Microsoft Access © application, a user manual and a workshop demonstrating its use. The NVCA later modified it for direct use on its website.