Determining how to reduce pollution across a 64,000-square-mile region is no easy task. With so many sources, and hundreds of ways to address it, state and local organizations can become overwhelmed with the task of reducing pollution. For over thirty years, the Chesapeake Bay Program partnership has provided tools to model what is happening in the region. Recently updated, this state-of-the-art suite of modeling tools will help state and local governments working with local partners to plan ahead and use limited resources effectively to reduce pollution.

Each of the six states that lie in the Chesapeake Bay watershed (Delaware, Maryland, New York, Pennsylvania, Virginia and West Virginia) and the District of Columbia has its own individual pollution reduction goals that it needs to meet. These goals were set in 2010 under the Chesapeake Bay Total Maximum Daily Load (TMDL) to help the Bay meet standards for water quality and later included in the 2014 Chesapeake Bay Watershed Agreement.

To help figure out how to meet these pollution reduction goals, each of the six states and the District of Columbia develops Watershed Implementation Plans (WIPs). To help create the WIPs, and to answer questions about pollution levels and sources, as well as impacts of pollution-reducing practices, developers and planners use the Chesapeake Bay Program’s suite of modeling tools.

This suite of modeling tools uses the latest science and real data (such as rainfall, river flow, and monitored water quality conditions) to replicate conditions of the Chesapeake Bay watershed. The suite of tools is actually made up of four different models:

  • Airshed Model: estimates the amount of nitrogen that falls onto the Chesapeake Bay watershed from the atmosphere, including sources such as vehicles and power plants.
  • Land Use Change Model: predicts the impacts that human and agricultural animal populations, development patterns and other changes to land uses will have on future nutrient and sediment pollutant loads to local waterways and the Bay.
  • Phase 6 Watershed Model: estimates the amount of nitrogen, phosphorus and sediment that reaches local waterways and the Chesapeake Bay based on different assumptions about pollutant-reducing practices and technologies put in place.
  • Estuary Model: examines the effects that changes in pollution loads from the surrounding Chesapeake Bay watershed have on the Bay’s water quality and biological resources.

The Phase 6 Watershed Model is the newest version, approved by the Chesapeake Bay Program partnership in December 2017. It has even more local data, including from industries not previously involved. The accuracy of the Watershed Model was confirmed by comparison with over three decades of water quality monitoring data collected at hundreds of stations across the entire watershed. It now provides more insight into how pollution loads have changed as pollution control practices have been implemented. Check out the Phase 6 Modeling Tools fact sheet for more highlights on how the model has improved.

Using data and inputs from many sources, the suite of models work together to answer questions about how different land use types or land management decisions can affect nutrient and sediment levels. The results are then put into the Estuary Model to predict how the Chesapeake Bay’s water quality conditions will respond to future conditions such as pollution loads and land use changes. The models can also simulate the environmental impacts of population growth, climate change and the sediment build-up behind the Conowingo Dam (on the Susquehanna River in Maryland), which can help decision-makers explore options to address these changed conditions.

An online version of the Phase 6 Chesapeake Bay Watershed Model—called the Chesapeake Assessment Scenario Tool or CAST—is available to anyone who wants to view and use this information. The modeling results help state and local governments, organizations, businesses and others identify which pollution prevention strategies and conservation practices make the most sense, given their available resources. It helps local planners better understand which pollution control practices can provide the greatest reduction in nitrogen, phosphorus and sediment loads, how much various implementation options might cost, and indicate which practices would be most successful given a geographic area.

Click here for more information on the Chesapeake Bay Program’s suite of modeling tools.

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