Modeling Tidal Dynamics and Tidal Datums along the Coasts of Texas and Western Louisiana

A tide model is being developed for the Northwestern Gulf of Mexico in support of VDatum, the National Oceanic and Atmospheric Administration's (NOAA) vertical datum transformation tool. The model domain extends from south of the US/Mexico border in the west to Atchafalaya Bay, Louisiana in the east. A high-resolution unstructured grid was created to represent the complex shoreline and fine bathymetric features. Efforts have been made to include most of the Intracoastal Waterway and to resolve the major navigational channels and barrier islands. The grid sizes vary from about 40 m along the channels/islands to 300 m along the coasts to 30 km at the open ocean boundary. The two-dimensional version of the ADvanced CIRCulation model is employed to simulate barotropic tides and depth-integrated tidal currents. Tidal datums, including mean lower low water, mean low water, mean high water and mean higher high water, as well as tidal harmonics, are derived from the simulated tidal water levels and validated against available observations at various tidal gauges obtained from NOAA's Center for Operational Oceanographic Products and Services and the Texas Coastal Ocean Observation Network. Tides in the area are mostly diurnal. K₁ and O₁ are of similar magnitudes and are the two dominant tidal constituents in the open coast. Both K₁ and O₁ amplitudes change only slightly in the coastal waters. However, M₂ amplitudes have a great spatial variability with magnitude comparable to the diurnal components over the northern Louisiana-Texas shelf. The results of sensitivity studies on the boundary conditions, bottom friction formulation, and other parameters are also described.