Tavit O. Najarian

A REAL TIME MODEL OF NITROGEN-CYCLE DYNAMICS IN AN ESTUARINE SYSTEM

A water quality engineering model, described by seven storage variables, for nitrogen-limited estuarine ecosystems is developed and used. Water quality trends and dynamic behavior of aquatic systems to varying environmental input conditions are examined. Simple batch-system analysis shows a limit-cycle behavior of the structured model. The inherent oscillations of the limit-cycle are damped when the batch system is opened to matter flows through its boundaries. Additional response analyses are conducted on an idealized estuary to compare “through-flow” models that ignore the tidal motion, with “real-time” models considering the tidal advection. The comparative analysis shows the influence of the hydrodynamic description of the flows on the spatial and temporal distribution of the nitrogen-cycle storage.variables in the idealized estuary.

Transient hydrodynamic and salinity simulations in the Chesapeake Bay network

A transient network model is applied to the Chesapeake Bay and its tributary estuaries. Calibration of the model is based on only three external parameters: a friction factor that is spatially described, and two global constants required to calibrate a dynamic dispersion relationship that depends on both the local salinity gradient and hydraulic conditions. The transient hydrodynamics and the transient salinity distribution of the Bay and its tributary estuaries are simulated for the period of one month and comparisons made between calculated and observed salinities.

Role of Models in Estuarine Flow and Water Quality Analysis

Mathematical models play a useful role in advancing the state-of-the-art in estuarine sciences, and in the judicious management of water resources in coastal environments. The validation of hypotheses related to flow and water quality behavior in tidal waters has been facilitated through the use of various models. The agony of guesswork in choosing the best management alternative within a watershed has been appreciably reduced due to model applications. Models have provided the means to analyze the impact of different management alternatives and selecting the ones which result in the least adverse impact to the environment. Models therefore, play an important role as tools for research and engineering assessment of estuarine flow and transport.

Conceptual Model for Back-Bay Inundations

Extra-tropical storms (“nor’easters”) inundate back-bay areas along the east coast of the United States. A simple analytical model is developed to simulate the sea-level response of small tidal embayments to nor’easters. The model’s formulation assumes a weakly nonlinear, pumping-mode response. The modeled response to subtidal forcing associated with extra-tropical storms has low-pass filtering characteristics – similar to the tidal response but with higher cut-off frequencies. For hydraulically constricted systems (i.e., systems having relatively small inlet cross-sections or large basins), the model simulates a damped tide and surge response, with the low-frequency surge damped less than the tide. For unconstricted systems, the model simulates a nearly un-attenuated tide and surge response, and a relatively high vulnerability to coastal flooding. Model results are summarized in the form of nomograph curves for various inlet/bay configurations and coastal storm characteristics. Results are compared both to numerical model simulations and to field data collected during a recent nor’easter.