5.10 Analysis and Modeling of Morro Bay, Califorina

Tuesday, 11 January 2000: 5:00 PM
Zhen-Gang Ji, Tetra Tech, Inc., Fairfax, VA; and M. R. Morton

The Morro Bay is a natural embayment located on the central coast of California. It is a shallow lagoon, approximately 6.5 km long in the north-south direction and about 2.8 km wide in the east-west direction at its maximum width. Due to sedimentation, the Bay has lost over a quarter of its volume over the last 100 years. At low tides, over 60% of the bay area emerges and becomes dry. Water quality concerns include excessive levels of bacteria, nutrients, and heavy metals. The purpose of this study is to develop a coupled hydrodynamic and sediment model for sedimentation control and water quality management in Morro Bay.

The Environmental Fluid Dynamics Code (EFDC) is used in this study. EFDC is a three dimensional and time-dependent model with the capability of simulating large wet/dry variability of tidal areas. The model employees seven prognostic hydrodynamic variables, a coupled twenty state variable water column eutrophication model with a twenty six state variable sediment biogeochemical processes model, and an unlimited number of sediment and toxic contaminant variables. The Morro Bay model grid contains 1609 curvilinear grid cells with resolution varying from 50 to 110 meters. The hydrodynamic calibration simulation includes a predictive, dynamically coupled simulation of salinity, temperature, and suspended sediment. The primary model hydrodynamic forcings included open boundary tidal elevations, freshwater inflows from two creeks, and surface wind stresses. The measured data for model calibration include tidal elevation, current velocity, water temperature, and salinity at 6 locations for 31 days, from March 9 to April 10, 1998.

Comparison between model results and data indicates that the model results match the data seasonably well at the 6 data stations for tidal elevation, current velocity, salinity and temperature. The model also simulates the wet/dry variability of Morro Bay realistically. Using the calibrated model, 160-day simulation and multi-year simulation are conducted to determine whether locations of sediment deposition are qualitatively in agreement with historical surveys. The model results indicate that sediment deposition occurred in the same locations as observed in the bay.

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