Title page for ETD etd-04282010-144026

Type of Document Master's Thesis
Author Bourgoyne, Mary Elizabeth nee Friedmann
URN etd-04282010-144026
Title Hydrodynamic Modeling of San Elijo Lagoon, California
Degree Master of Science in Civil Engineering (M.S.C.E.)
Department Civil & Environmental Engineering
Advisory Committee
Advisor Name Title
Willson, Clint Committee Chair
Cable, Jaye Committee Co-Chair
Smith, Heather Committee Member
  • Hydrodynamic
  • Modeling
  • Mike21
  • San Elijo Lagoon
  • Danish Hydraullic Institute
  • Coastal
  • Berylium
  • Sediment Transport
Date of Defense 2010-03-19
Availability unrestricted
Decisions on where to concentrate management efforts need to be guided by an ability to accurately simulate and predict physical and ecological changes. Many restoration projects experience difficulties due to a lack of understanding of the ecological response and evolution of wetland systems (Goodwin et al., 2001). There are several approaches that can be taken in analyzing a system. The appropriate selection should be based on the available data, the spatial scale of the wetland, and the physical processes governing the system (Goodwin and Kamman, 2001). Predictive tools are essential for good long-term management (Goodwin et al., 2001). The objective of this thesis is to determine whether San Elijo Lagoon is a morphologically stable environment and to investigate the movement of water and sediment patterns within the estuary. This will be answered through analysis of field data and numerical modeling of the hydrodynamics of the system. A field campaign was conducted to collect a suite of hydrodynamic and sediment data in the estuary. The development of a conceptual model was further applied to a numerical model. The Danish Hydraulic Institute’s (DHI) Mike21 software package was used to develop a two-dimensional flexible mesh hydrodynamic model. This is a depth-averaged finite volume commercial program. The hydrodynamic model was calibrated with the data collected in May, and then verified with observed conditions from July and August. The lagoon has a net depositional environment. The inlet of the lagoon is unstable due to the enforced unnatural location and meandering morphology of the inlet channel; the force of the tide is not large enough to keep the inlet clear. MIKE21-FlexibleMesh model simulations confirm that San Elijo Lagoon’s hydrodynamics is dominated by tidal forcing and freshwater inflow. The freshwater inflow, as well as the morphology of the lagoon causes an attenuation of the tidal signal. In the coincidence of extremely low tides and extremely high runoff in the watersheds feeding the lagoon the freshwater inflow at the man-made dike can have a significant impact, but only for a short period of time.
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