For two decades water quality models have been employed in the Chesapeake Bay watershed. The first application was the Watershed Model. Completed in 1982, the first version of the Watershed Model established the importance of nonpoint source loads in the Chesapeake. The simulation period
for this model was for three years, covering a spring to fall period. The next phase of modeling linked a refined HSPF (Hydrologic Simulation Program – Fortran) based watershed model to an estuarine water quality model. These two models assisted in the establishment of the Chesapeake
40% reduction goal for nutrients. The simulation period for these models was three years. For the water quality model a summer average period was simulated. The next phase of Chesapeake modeling linked an airshed model RADM (Regional Acid Deposition Model) to a much refined watershed
and estuarine simulation. Using a refined grid in all of the simulations, and a simulation period of eight years for the watershed model and four years for the estuarine model, these models were used to establish the nutrient load allocations for the major basins of the Chesapeake. A subsequent
version of the linked airshed, watershed, and estuarine models included simulations of underwater grasses in the Chesapeake as well as benthic organisms. This version of the cross-media models, applied in 1998, was used to further examine tributary allocations in the lower Bay. Current
versions of the cross-media models are being applied to estimate load allocations for nutrients and sediment in the Chesapeake in order to “remove all water quality impairments by 2010” [Chesapeake 2000 Agreement]. Current and future models of the Chesapeake cover a simulation
period of fifteen years or more and are being developed as “community models” with model code, preprocessors, and postprocessors made available over the web as freely available, open source, public domain simulations. Users include local, state, and federal governments, researchers,
students, and other water resource professionals. The next generation of crossmedia models of the Chesapeake, like the preceding versions, will assist in developing water quality controls that are protective of the environment, equitable, and cost effective. The “community model”
approach should lower costs of model application and make modeling tools of the Chesapeake more broadly applied.
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