| dc.description.abstract | Previous studies have pointed out that discrepancies may arise between the total water level and the observed data after accounting for residuals when examining storm surge water levels in model simulations. Possible factors contributing to these discrepancies include the impact of extreme events, unique topographical features of specific areas, and the positioning of tide gauges inside harbors rather than in open waters. Therefore, it is necessary to examine the effects of pure storm surge water and astronomical tidal levels separately. However, even when examining tidal water levels alone, fluctuations in water level values can still occur, indicating that factors other than storm surges may affect the accurate identification of water levels.
To understand the water level residuals, this study employed the COMCOT-SS numerical model (Cornell Multi-grid Coupled of Tsunami Model—Storm Surge) along with the TPXO8-atlas astronomical tide model as boundary conditions. By solving nonlinear shallow water equations, the study simulated water level results at several existing tide gauge stations during specific pure tidal periods and conducted convergence analysis of statistical parameters, revealing the potential impact of tidal arrival times on total water level residuals.
Various variables were considered in exploring the temporal effects of harbor structures on water levels, including Manning′s coefficient, wave height, the distance between tide gauges, and water depth. To establish relationships between these parameters, this study conducted a dimensionless analysis of wave speed using the simplified characteristics of harbor topography. The dimensionless parameter I_z (calculated as I_z=C_s/C_p, where C_s is the simulated wave speed obtained from the distance between two different tide gauges and the arrival time of the incoming wave; C_p is the predicted wave speed calculated using the formula C_p=√gH, where g is the gravitational acceleration, H is the water depth) was used to record the effects of harbor structures on the time differences in water levels inside and outside the harbor, observing the potential impact of harbor structure shielding on wave speed simulations. Subsequent water level analyses were conducted for actual harbor cases to assess the influence of different variables on the timing of water levels.
The study found that the dimensionless parameters x_1, x_2 and x_3, derived from three different variables (wave height h, Manning′s coefficient n, and water depth H), could potentially contribute to timing errors in water levels. It was also noted that the dimensionless parameter x_2, calculated from Manning′s coefficient n, was negatively correlated with the dimensionless wave speed parameter I_z. In contrast, the dimensionless parameter x_1, calculated from wave height h, was positively correlated. Ultimately, an empirical formula was derived through linear regression analysis of all data points, which, when compared with actual harbor simulation cases, confirmed its applicability in assessing the differences in wave speeds and timing between tide gauges inside and outside harbors.
Future research can reference this study′s use of nested grids, selection of numerical tide gauges, and simplified terrain settings. Analyzing the relationship between variables and the dimensionless parameter I_z of wave speed can achieve more accurate water level analyses. Furthermore, the method of designing empirical formulas developed in this study could be applied to various fields, including estuarine and river assessments or evaluations of wave speed and tidal arrival time for tidal energy generation. | en_US |