Development of a eutrophication model and its application to the Newport Bay Estuary, California

A finite element water quality model was developed and applied to Newport Bay, California, to determine the eutrophic state within the water body. A two phase research effort was conducted for this dissertation. In Phase I, a diffusion hydrodynamic model (DHM) was developed by neglecting local acceleration and inertial terms. The model utilizes the integrated finite difference method explicit in the time domain. The model was verified and calibrated by comparing model simulated results and collected data. Application of a DHM with four sided irregular polygons to a shallow estuary marks the first application to this class of model. Quadrilateral discretization of the bay reduced the number of computational cells by about 30 percent compared to a regular grid system. An automatic time step size selection procedure was developed for the DHM which resulted in CPU time savings as much as 40 percent. Watershed contributions of surface runoff was incorporated in the DHM to simulate specific storm event conditions within the Bay. The Soil Conservation Service (SCS) method was used to generate surface runoff hydrograph. This model (DHM) is an integral part of the water quality model, developed in the Phase II of the research.;The water quality model utilizes the finite element method (FEM) with a linear basis function. The FEM approach uses a domain transformation that reduces the size of the stiffness and capacitance matrix by an order equal to the number of specified boundary condition nodes. The model simulated eutrophication conditions by using conceptualized eutrophic variables as model species. Bacterial transport and bacterial action on eutrophication was also studied. The model was calibrated for total dissolved solids (TDS) data at eight stations from Newport Bay. The model was then applied to Newport Bay to determine nutrient conditions. Simulations indicated that the lower portion of the bay has a more or less uniform spatial species concentration. The upper portion of the bay has some locations susceptible to nutrient accumulation. Several eutrophication control strategies were also explored. It was observed that the accumulation of any species did not occur during large storms. Point/nonpoint source pollution control strategies indicated that the time span required for the improvement of water quality may be of the order of decades (depends on the desired percent of improvement). The bay nutrient limiting conditions and a detailed control strategy should be further investigated.