Phase 7 Model Development

In Progress

These updated modeling tools will be used by the Chesapeake Bay Program partnership to inform decisions related to the nutrient and sediment reduction goals outlined in the revised Watershed Agreement.

Description

Currently in development, the Phase 7 Model project is focused on updating the tools for the Chesapeake Bay TMDL relating nitrogen, phosphorus, and sediment reductions to improvements in tidal dissolved oxygen, clarity, and chlorophyll. Integral to this updated suite of tools is the ability to project changing environmental conditions through 2035. The model, which will be ready for use by 2028, consists of eight interrelated projects: 

  1. High Resolution Land Use
  2. Chesapeake Assessment Scenario Tool (CAST)
  3. Optimization
  4. Agricultural Inputs
  5. Atmospheric Deposition Modeling
  6. Watershed Modeling
  7. Estuarine Modeling
  8. Criteria Assessment.

How are these projects interrelated? - CAST is a publicly available model of the Chesapeake Bay watershed used to estimate changes in long-term nutrient and sediment loads due to changes in point sources, land use and land management. Watershed modeling provides the science behind the calculations in CAST while optimization allows users to find a least cost management option in CAST for a given nutrient and sediment reduction. The production of new high resolution land use data and the improvement of agricultural inputs will inform and improve the phase 7 watershed modeling products while also providing important data for other CBP goals and outcomes. Estuarine Modeling translates changes in nutrients and sediment to water quality outcomes in the tidal waters of the Bay. Criteria Assessment is the process of determining whether the predicted water quality outcomes meet state water quality standards. 

The development of the Phase 7 model is ongoing. Evolving plans and related documents will be posted here as they become available. More information on the role of the model in the Chesapeake Bay Program, and why this update is happening can be found on the Modeling Page.

A diagram of the inputs to the model flowing into the watershed model and estuary model which yield the impacts and results we are measuring.

Resources

Partnership Planning Documents

High Resolution Land Use

Contact - Peter Claggett and Sarah McDonald | Land Use Workgroup

High resolution land use products are developed at the meter scale for Phase 7. These will go directly into the watershed modeling efforts and provide information for other CBP partnership goals and outcomes. Changes to the classification schema for Phase 7 include redistribution of classes under mixed open and the addition of two solar classes, a construction class, and a harvested forest class.

Chesapeake Assessment Scenario Tool (CAST)

Contact - Jess Rigelman and Auston Smith | Water Quality GIT and Watershed Technical Workgroup

CAST is a publicly available model of the Chesapeake Bay watershed used to estimate changes in long-term nutrient and sediment loads due to changes in point sources, land use and land management. CAST will receive upgrades to improve transparency and usability as part of a project that will also redesign the process for submitting management practice data. A spatial interface to CAST will be designed to give output for a user-defined spatial extent.

  • Phase 7 Land Use/CAST Load Sources Crosswalk Table (Sep 2025) - Aggregation of High-Resolution Land Uses to Phase 7 Mapped Land Uses and the corresponding Phase 7 CAST Load Sources. It also includes loading rate ratios for each load source.
  • Phase 7 CAST Load Sources (Presentation: Sep 2025, WQGIT) - Outline of the Phase 7 CAST Load Sources by Agriculture, Developed, and Natural sectors, highlighting any new land uses and changes from Phase 6.
  • CAST Updates Timeline (Presentation: Feb 2024) - Gantt chart and outline of planned activities for Phase 7 CAST work.

Optimization

Contact - Lew Linker | Modeling Workgroup

Optimization software is being developed so that CAST scenarios can be generated representing the least cost to achieve a desired level of nutrient and sediment reduction.

Agricultural Inputs

Contact - Tom Butler | Agricultural Modeling Team

The Agricultural Modeling Team (AMT) was created to examine and revise the agricultural inputs to CAST. The goal is to achieve a realistic representation of the nutrients from manure, commercial fertilizer, fixation, crop uptake, soil storages, and other agricultural inputs over time.

Atmospheric Deposition Modeling

Contact - Lew Linker | Modeling Workgroup

The CBP is using the EPA's Community Multiscale Air Quality Model (CMAQ) model to track atmospheric deposition of nitrogen. The latest version of the CMAQ model will be used as input loading to the watershed model. A source apportionment model (CMAQ-ISAM) will be used to estimate changes due to proposed emission reductions beyond State Implementation Plans.

Watershed Modeling

Contact - Lew Linker | Modeling Workgroup

The watershed model underlying the CAST calculations is being updated for better representation of physical processes, improved nutrient application calculations, and variable-scale modeling.

Estuarine Modeling

Contact - Lew Linker | Modeling Workgroup

A new estuarine model is being developed for the entire tidal Chesapeake (the Main Bay Model or MBM) incorporating the latest techniques. Multiple Tributary Models (MTMs) are also being developed as testbeds for improved overall model performance.

Criteria Assessment

Contact - Peter Tango | Bay Oxygen Research Group and Hypoxia Collaborative Team

The estuarine water quality criteria assessment procedures are being considered for revision based on changing environmental conditions. A separate effort looks to create a new Bay interpolator using vertical profiler data to generate DO estimates across space and through time, improving upon the current spatial interpolation used in the Chesapeake Bay. The output of the tool will allow for expanded evaluation of short-duration criteria and aid in habitat assessments.