Currently in development, the Phase 7 Modeling Tools will be used by the partnership to inform decisions related to nutrient and sediment reduction goals outlined in the Chesapeake Bay Watershed Agreement. Integral to this updated suite of tools is the ability to project climate change effect through 2035. The model, which will be ready for use by 2027, consists of seven 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

Interactive segmentation viewer of the airshed, watershed, and estuarine models

How are the 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 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. Some of the projects will also be used to track CBP goals other than the TMDL and are represented as crossing the Phase 7 boundary.

Partnership Planning Documents

High resolution land use

CBPO lead – Peter Claggett

High resolution land use products are being developed at the meter scale for delivery in 2024. They will go directly into the watershed modeling efforts and provide information for other CBP partnership goals and outcomes.

The USGS Land Data Team has formally published statewide mosaics of the 2017/18 Land Use/Land Cover data and change from 2013/14 to 2017/18 on here: Enhancements to the land use classification schema are under development for the 2021/22 land use data including the addition of animal operations and the separation of pasture from hay.

View the current upgrade timeline (5/6/2022)

View the current planning document (5/6/2022)

View a recent presentation (4/24/23)‍

View a description of high-resolution data sets (5/2/23)‍


CBPO Lead – Olivia Devereux

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.

View the current upgrade timeline presentation (2/26/2024)‍


CBPO Lead – Lewis Linker

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.

View the current planning spreadsheet

View a recent presentation (1/9/2024)‍‍

Agricultural Inputs

CBPO Lead - Tom Butler

The Agricultural Modeling Team will 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. As of September 2022, the Team is in the process of being formed by the Agriculture Workgroup.

View the current workplan

View the Agriculture Modeling Team page

View a recent presentation (1/9/2024)‍‍

Atmospheric Deposition Modeling

CBPO Lead – Lewis Linker

The CBP is using the EPA's Community Multi-scale Air Quality (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

View a recent CMAQ presentation (4/5/2022)

View a recent CMAQ-ISAM presentation (10/17/2023)

Watershed Modeling

CBPO Lead – Gary Shenk

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

View the current planning spreadsheet

View the current process flowchart

View a recent presentation (6/20/2023)‍

Estuarine Modeling

CBPO Lead – Lewis Linker

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) will also be developed as testbeds for improved overall model performance.

View the current planning spreadsheet

View a recent MBM presentation (1/10/2024)‍‍

View a recent MTM presentation (1/10/2024)

Criteria assessment

CBPO Lead – Peter Tango

The estuarine water quality criteria assessment procedures are being considered for revision based on climate change considerations. A separate effort looks to create a new Bay interpolator using vertical profiler data which can evaluate criteria which could not previously be evaluated. The collection of data is being coordinated through the Hypoxia Collaborative Team and the development of data analysis methods is coordinated in the Bay Oxygen Research Group.

View the current project overview

View the Hypoxia Collaborative Team webpage

View the Bay Oxygen Research Group webpage

View a recent presentation (4/24/2023)‍