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-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.

    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

    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 may be downloaded using the link below.

    Not all of 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. 

    Phase 6 Model Review Sessions

    Webinar-based model review sessions provide the Chesapeake Bay Program Partnership with the opportunity to directly ask questions and provide feedback on the model. Click on the links below to view and hear the recorded webinars.