Analysis of tidal variations of Lake Pontchartrain and the Mississippi Sound

"The National Ocean Service is involved in a cooperative marine boundary program with the State of Louisiana for the determination of tidal datums. Water level variations are analyzed to study the transition from tidal to nontidal regimes. The potential effects of the transition on tidal datum computations are evaluated. The changes in tidal characteristics are evaluated using comparison of tabulations of high and low waters, using time series plots and cross-spectral analyses of hourly heights, and using reduction or variance statistics from harmonic analyses. It was found that proceeding into Lake Ponchartrain from the Mississippi Sound, the effects of tidal forces on the water level are reduced, especially at the semidiurnal frequencies, and the effects of meteorological events and seasonal meteorological patterns on the water level are increased. Effects of meteorologically induced seiches in Lake Pontchartrain can also dominate water level variations for short time periods of one to three days. The observed low signal-to-noise ratios can result in complications when computing tidal datums."