The Chesapeake Bay experience

Due to the decline in the water quality of the Chesapeake Bay over the past 30 years or so as a result of excess loading of nutrients, the Chesapeake Bay Program (CBP) has been involved in the development of numerical modeling tools to aid in the assessment of various nutrient controls. The CBP is a voluntary partnership that includes the states of Maryland, Virginia, and Pennsylvania; the District of Columbia; the Chesapeake Bay commission (a tri-state legislative body); and the US Environmental Protection Agency (EPA). The CBP's initial strategy was to develop a quasi-three dimensional (3D) steady state hydrodynamic and water quality model along with the watershed model. Following this effort, the US Army Corps of Engineers jointly funded with the CBP the development of fully 3D time varying hydrodynamic and water quality models with output loads obtained from the watershed model. That effort focused on the main Bay with the tributaries rather coarsely resolved in the numerical grid. In addition to the main bay, current effort focuses on the tributaries. This effort has seen the continued development of the 3D hydrodynamics and water quality models and the watershed model along with the development of another modeling component, i.e., an airshed model, to provide nutrient loading from the atmosphere. The integrated suite of models will be used to simulate the impact of nutrient control scenarios. The various modeling components are discussed and results from the hydrodynamic model are presented. Calibration of the current water quality model, which includes submerged aquatic vegetation and higher trophic levels, is ongoing.