Wind-wave measurements in a shallow estuary: Trinity Bay, Texas

Acoustic current meter data collected in the shallow ( 3m depth) Trinity Bay, (TB a sub-bay in Galveston Bay), TX, estuary were used to characterize locally generated windwaves. Significant wave heights, periods, and directions were estimated from dynamic pressure time-series (P; near bottom) and horizontal current velocities (U, V). Surface wave spectra were calculated from the pressure time-series and fitted to the empirical shallowwater Texel, Marsen, and Arsloe wave spectrum. The mean shape parameters used to define the TB wave spectra were:alpha = 0:016, gamma = 4:26, sigma-a = 0:063, sigma-b = 0:089. Waves heights were also hindcast using empirical and numerical models. The empirical formulas were derived from fetch-limited shallow water observations and follow the current proposed asymptotic limit to wave growth in shallow depth. The depth range for this empirical formulation is extended from 0.5?2m out to 3.5m. The model does not work for wind speeds less than 1m/s and during rapid wind direction changes. The Shallow WAves Nearshore numerical model was implemented in a Galveston Bay (GB; encompassing TB) computational domain. The model was forced with wind speeds and directions measured on-site and in four surrounding locations maintained by the NOAA PORTS. Currents measured on-site in TB and calculated bottom frictions were input homogeneously in space. The model was run in steady and unsteady conditions, and the modeled wave spectra were compared to the observations. The modeled wave spectra do not recreate the observed spectral shape for the steady and unsteady conditions. However, the total wave energy is represented in the unsteady conditions. In both the steady and unsteady cases, the wave period is underpredicted by one-half times the observed spectra and the model direction agrees with the observed wave directions.