Model Documentation

Suggested Citation

Chesapeake Bay Program, 2020. Chesapeake Assessment and Scenario Tool (CAST) Version 2019. Chesapeake Bay Program Office, Last accessed [Month, Year].

CAST-23 version

CAST-23 is planned to be the last model update to the phase 6 suite of models. This follows the decision to update the CAST schedule, which was approved by the Water Quality Goal Implementation Team, Management Board, and Principals' Staff Committee. The decision can be found in the September 26, 2023 PSC meeting minutes. CAST-23 contains all the planned updates for CAST-21 plus:

Additional CAST-23 related resources are linked below.

CAST-21 version (never released)

BMPs in progress scenarios are pulled from the National Environmental Information Exchange Network (NEIEN), and used to update that year's progress data. This means that new inspections, new cumulative BMPs in any year, and new annual BMPs are used for that year's progress. The prior years' progress scenarios are not updated. However, when changing to a new version of CAST, all years' progress scenarios are updated to include new BMP history.

CAST-19 version

CAST-17d is updated to CAST-19 with changes to data and BMPs used in the Phase 6 model for the milestone period. This follows the Principals' Staff Committee decision of July 9, 2018 that changes are made only in advance of the two-year milestone period. The decision can be found in the July 9, 2018 PSC meeting minutesThese changes were agreed to by the WQGIT and its workgroups. The changes are limited in scope so that they do not: 1) impact modeled runoff during the 1993-1995 critical period; or 2) alter the base conditions (land uses, septics, animals, etc.) from 1984 through 2013. Preservation of these estimates enables a consistent assessment of how new management actions and changes in base conditions have influenced loads over time.

Climate Change

Results of updated methods, techniques, and studies that are used to develop an estimate of pollutant load changes (nitrogen, phosphorus, and sediment) due to 2025 climate change conditions. Planning targets for the TMDL, climate change, and Local Area Planning Goals are available.

Climate Change Documentation

Phase 6 Dynamic Watershed Model and CAST-17 documentation

The documentation is for the dynamic and time-averaged Watershed Model. CAST is the same as the time-averaged Phase 6 Model. Creating and running scenarios in CAST is simply using an on-line interface to the time-averaged Model. Due to the length of the documentation, it is divided into sections. Click on the links below to read through the different portions of the documentation.

Phase 6 Model Performance

More information on the Watershed Model can be found at the Modeling Workgroup page.

Phase 6 STAC Review

Non-Tidal Water Quality Dashboard

Comparisons between the modeled and monitored data can be found on the non-tidal water quality dashboard. These visual representations show both the loads estimated from the U.S. Geologic Survey's Weighted Regressions on Time, Discharge and Season (WRTDS) and loads estimated from the time-variable Phase 6 Watershed Model.

Non-Tidal Water Quality Dashboard

The Chesapeake Bay Nontidal Monitoring Network Loads and Trends page shares the short-term water year nutrient and suspended-sediment load and trend results and background information for the Chesapeake Bay Program's nontidal network (NTN). It provides primary findings for nitrogen, phosphorus, and sediment trends and examines results for river basins for individual sites.

Chesapeake Bay Nontidal Monitoring Network Loads and Trends

Graphical Interface to the Phase 6 Watershed Model Inputs

Graphs and maps of the inputs to the Phase 6 Watershed Model for all versions, along with the option to download the source data, is provided to facilitate transparency and offer a common, public platform for reviewing data.

Due to the size of the datasets required to present this information, the Graphs and Maps have been divided into the following categories.

The calibration land use data is available on the Nutrient Applications link above. It is shown in maps with the ability to filter by sector, land use, and agency. The tabular land use for years between 1984 and 2013 is available upon request.

    Not all the inputs are applied to each of the load sources. For example, manure nitrogen and phosphorus are not attributed to developed lands. Only leguminous plants fix nitrogen, so the fixed nitrogen input only applies to load sources that may contain crops or plants that are leguminous. The table of Loads by Load Source provides a ready reference of the inputs for each load source.