Chesapeake Assessment Scenario Tool (CAST) is the Chesapeake Bay Program’s Watershed Model. CAST provides estimates of average annual loads that would be expected given ten years of typical weather conditions. Figure 1 shows annual mean total nitrogen and phosphorus loads in the Chesapeake Bay watershed for the year 2017 simulated by CAST. CAST uses multiple models and multiple lines of evidence from scientific observations wherever possible to estimate these loads. CAST is also a web-based nitrogen, phosphorus and sediment load estimator tool that streamlines environmental planning. It is used to set planning targets, design implementation plans, and track the progress in implementation of nutrient reduction efforts for achieving Chesapeake Bay Total Maximum Daily Load (TMDL) targets.
Figure 1: Spatial sources of total nitrogen (left panel) and total phosphorus (right panel) loads simulated by the time-averaged Chesapeake Assessment Scenario Tool (CAST). These maps represent annual means for 2017.
CAST estimates of load reductions for load sources include: agriculture, developed, natural, wastewater, and septic loading to the edge of a small stream and loads delivered to the tidal portion of the Chesapeake Bay. CAST stores the geographic area, cost and implementation level associated with each BMP as well as the load for each sector and land use. With these data tables, CAST also serves as a data management system. Thus, users may quantify the impacts of various management actions while improving local management decisions.
CAST users can specify a geographical area, and then select Best Management Practices (BMPs) to apply on that area. CAST builds the scenario and provides estimates of nitrogen, phosphorus, and sediment load reductions. The cost of a scenario is also provided so that users may select the most cost-effective practices to reduce pollutant loads. CAST enables planners in the watershed to develop a plan for meeting a nitrogen, phosphorus, or sediment load allocations using the most cost-effective strategy. CAST can be used to answer questions about the effect of different BMPs on loads, the impact of land use development over time, and to identify the geographical location where BMPs will reduce the most load. CAST allows users to understand which BMPs provide the greatest load reduction benefit, the extent to which these BMPs can be implemented, and the cost of these BMPs.
To find out more about CAST, and get access to it, visit: https://cast.chesapeakebay.net.