| This research integrates mathematical hydrodynamic, water quality, and ecological models to provide quantitative spatial and temporal assessments of impacts of multiple stresses on aquatic ecosystems. Stresses can occur naturally, such as low flows and high water temperatures during a drought, or they may be anthropogenic, such as flow regimes that are modified by reservoir or pumping operations. Alternative strategies for protection and restoration of sensitive aquatic species may modify environmental stresses. The modeling methodology presented here allows physically based assessment of impacts of management alternatives on aquatic ecosystems under conditions of unsteady flow in riverine and estuarine systems.; To assess impacts of management alternatives on species sensitive to environmental stresses, a mechanistic approach has been developed that integrates mathematical hydrodynamic, water quality, and ecological models. A hydrodynamic model, RMA-2, provides dynamic descriptions of water velocity and depth throughout modeled riverine and estuarine systems based on reservoir operations, system withdrawals, tributary inflows, and tidal influences. Simulated hydrodynamics are then utilized by a companion water quality model, RMA-11, to simulate water quality constituents such as water temperature and salinity. Finally, the combined outputs of the hydrodynamic and water quality models provide descriptions of the physical and chemical environment to an ecological model, SAMTRK, a particle-tracking model developed in this research to simulate survival and out-migration of individuals or groups of juvenile chinook salmon. This approach is unique in that assessment of impacts of management alternatives considers coupled hydrodynamic, water quality, and ecological responses at refined spatial and temporal scales.; The Sacramento River-San Francisco Bay-Delta system in Northern California was selected for preliminary calibration, sensitivity testing and application of the modeling approach. In recent years, environmental stresses in this system, such as those imposed by modified flow regimes and excessive water temperatures, have contributed to declining salmonid populations. Several proposed water resource management alternatives have been examined with the new methodology to assess potential impacts on juvenile chinook salmon. It is believed that improved understanding of aquatic ecosystem response to management alternatives gained from applying this modeling approach will aid in securing practical solutions for preservation of aquatic habitat and threatened species. |
